Electromechanical way of detecting ultra low currents - Page 1
Forum section: electronics / projects

author: LondonNight
author_rank: Contributor
timestamp: October 25, 2020, 04:19:59 pm
content: Hello. I have been working on an 8 bit relay computer (details about the computer here:www.cemprelaycomputer.com), and I want to use some sort of phisical storage medium for storing programs.I have been thinking mainly about punched paper tape, and magnetic tape. I would rather prefer magnetic tape for reasons I won't list now, but if magnetic tape will prove to be impossible to implement in my situation, I will have to resort to using punched paper tape. Anyway, I need an idea of the best way to convert data which is stored on magnetic tape into an actual signal that could actuate any sort of relay... because here's the catch with this computer: I can not use any sort of solid state devices, I cannot use transistors, diodes, vacuum tubes and such. Capacitors and all the other components which did exist in the early era of relay computers are allowed.Now, I know that magnetic tape did not exist in the relay computer age, but I will allow it for convenience. The only difficult part is finding a way of interfacing relay technology with magnetic tape technology...I have thought of getting a magnetic tape head reader, the kind which was used in audio tape cassette players, together with ordinary audio cassettes, and record on the tape a 1000Hz signal for logic 1, and audio silence for logic 0 (bitrate really does not matter here, the storage medium can be really as slow as it wants, even 1 bit per second is well enough, all that matters is that it works) and have the magnetic tape head feed into an AC relay, so the computer could pick up the data from there... so here are the options:I either:a) find an AC relay which can work with such low currents/voltagesb) find a way to amplify that signal and THEN feed it into a relayc) give up and use paper tape insteadI would really really not want to use paper tape. Anyway, I have thought recently of galvanometers, perhaps using one/making one actuate some sort of contact? Then again, that brings its own set of problems, two contact pads being actuated by a galvanometer's coil would not have any sort of reasonable force pressing them together, and I imagine the bounce would be quite a problem.Another idea that came to mind was to use both the right channel and the left channel output of the tape head in series, to increase the voltage, or maybe in parallel, to increase the current... Also, a normal cassette tape has 4 tracks on it, so maybe I could get a head to read them all at the same time, and maybe use a series/parallel of those outputs to further increase my signal? or even having 2 tape heads one after the other, again, put in series/parallel? Then I thought I could also increase the tape's speed, so that the head/heads generate a higher level signal? Then I thought I could also perhaps use old VHS tapes, but instead of having a rotating drum like in a normal VHS reader, I could have a very big head similar to normal audio cassette heads? Surely that would make an even bigger signal, having an even higher chance of being detected by electromechanic means...Those are all my ideas of approaching the problem, and despite not testing any of them, I really think none of them would do the job. I am curious what you guys think may be the best approach to this problem, and what sort of ideas you could come up with. After all, there are loads of very clever people here!I will definitely test some of my current ideas in the following days, especially the VHS tape one, maybe it will go somewhere... but until then, I'm curious what you guys think

author: coppercone2
author_rank: Super Contributor
timestamp: October 25, 2020, 05:08:59 pm
content: i think if you are trying to get a dial on an instrument to actuate something it will be difficult to get reliable stickingI think you would need very clean gold of the correct alloy in a clean hermetic seal (I think normal gold might be too sticky). I imagined a hair attached to the back of a dial in a analog instrument. I have a feeling it will be a very long while before you figure out how to tune such a sensitive system and make the novel electromechanical contacts (to my knowledge).You could try silver? plating a galvenometer needle and replacing the end stop peg with a metal conductor but the bearing system might not be conducive to carrying current, so you might want it to bridge a contact there instead of using the needle as the main part of the conductor (think of it as putting a shunt between two terminals).

author: LondonNight
author_rank: Contributor
timestamp: October 25, 2020, 05:14:17 pm
content: Yeah, I fully agree... There must be a way to do it differently tho

author: coppercone2
author_rank: Super Contributor
timestamp: October 25, 2020, 05:15:38 pm
content: Quote from: LondonNight on October 25, 2020, 05:14:17 pmwhat is the force behind a galvenometer needle (the range of current operation for full scale?)Get the biggest one you can, wrap the needle in a very thin strand of wire (i.e. pulled out of a multimeter test lead), then inside the meter replace the end stop peg with a metal peg wired to a circuit and then add another peg, so the copper wrapped needle bridges two pegs.Then slam the galvenometer with a slight overrange. If you wrap it enough and make it bumpy and perhaps you need to sand down the needle to make it more floppy (so its like a whip rather then being beaten with a stick so it deforms over the contacts with its irregular copper wire wrapped surface (think like a knife handle with paracord)) it might work. You might also benefit from replacing the needle with a floppy plastic wrapped in the wire.It does not need to indicate super well anymore so you can get away from the stiffness to try to increase contact area.Then you would need to hook it up to a relay tester to measure the contact resistance and leave it on cycle for a while to see if it changes. That would be interesting to see actually.Oh right, and you might need to play with balance of the needle, if you add copper to it. Very very thin gold wire is also an option if you can source it, or perhaps RTD wire made of platinum, which is readily available if you carefully destroy a RTD sensor. I broke one once and the wire was loosely spooled up on a bobbin and unwrapped easily. A good one will not be glued because the glue adds parasitic strain error to the span of the sensor.RTD wire might be your best bet, because it should be extremely inert being platinum.

author: LondonNight
author_rank: Contributor
timestamp: October 25, 2020, 05:35:23 pm
content: This idea is worth considering. Maybe even increasing the magnetic field somehow may help? Perhaps with a huge electromagnet? hmmmmm.....

author: Gyro
author_rank: Super Contributor
timestamp: October 25, 2020, 05:39:40 pm
content: Back in the day, thereweregalvanometer relays that used a large moving coil and magnet and light Platinum contacts. There were also smaller, more robust versions (still moving coil) used for high speed telegraphy. You might strike lucky.

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 25, 2020, 05:52:41 pm
content: How about use a tube amp? It won't look too out of place in a piece of retro equipment.

author: SilverSolder
author_rank: Super Contributor
timestamp: October 25, 2020, 06:05:21 pm
content: I like the idea of recording 1KHz tone pulses on tape, Morse code style, for this project.All you have to do is to play the pulse train back using an audio tape player - just rectify the speaker output with a diode to turn it into a DC pulse instead of an AC one, and then use that resulting DC pulse to drive a small relay directly. It ought to be fairly easy to get this to work!

author: Twoflower
author_rank: Frequent Contributor
timestamp: October 25, 2020, 06:13:03 pm
content: Not sure how well, if at all, it would work. But if you use a matching tuning fork (1kHz) magnetically coupled as resonance amplifier. Using a voice-coil to make the tuning fork oscillate if the tape-head sees a 1kHz tone.To 'read the tuning fork you might either use a contact that gets closed (at 1kHz) if the fork oscillates or using a second coil to read out the amplified pulse. Amplified because the fork accumulate the energy of the 1kHz tone, so the readout would get higher and higher if the tone stays on longer (ignoring any damping here).You probably need a very low-mass tuning fork to give a reasonable fast response with low energy needed to excite it. And a permanent magnet would probably also help but that mass needs to be taken into account for the tuning. But that would potentially weaken the signal on the tape (overwriting the signal)....just thinking aloud...

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 25, 2020, 07:07:23 pm
content: Quote from: Twoflower on October 25, 2020, 06:13:03 pmI'm not sure that you mean exactly what you're saying, but you might not be far off, it's just a bit more complicated:- Reading tone modulated audio is a reasonable idea; it's certainly been done historically. Essentially a tape recording of a modem's output. Which can be pretty slow, a few hundred baud for example, which is dozens of cycles at low kHz, easy to get a good reading on.- And reading it with a tape head is a good idea, the magnetic gap is small and precise, they're cheap and available, and the signal can be coupled to anything else electromagnetic, of course as long as you don't mind that the signal is pitifully small...- A tuning fork is no amplifier. A resonator can only filter what energy is given it. You can get a large peak amplitude (in terms of displacement or force), and you can get more peak power (by discharging that amplitude in a transient event), but you aren't getting any more energy than you start with.- But, suppose we had a resonator already with energy in it, and used a nonlinear coupling to a resonator tuned to a different frequency, and varied that coupling with the magnetic field, or something like that. We could make a parametric amplifier...- Magnetic amplifiers can also be used, if you don't mind that there is a active material in the solid state (a pile of ferrite cores).Neither is all that easy to design or build, unfortunately; I've not made a par amp myself, and only a few experiements in mag amps.I do find it an amusing idea, something like: bowing a wine glass spinning on a shaft, coupling that to something, coupling the audio signal to it, and extracting the amplified signal then detecting it somehow. All mechanical and acoustic, with magnetic coupling as needed.Tim

author: Twoflower
author_rank: Frequent Contributor
timestamp: October 25, 2020, 07:24:56 pm
content: Quote from: T3sl4co1l on October 25, 2020, 07:07:23 pmI had asinusoidal driven harmonic oscillatorin mind. The point is that the resonant tone persist over a certain time the fork might accumulate the energy from the tone thus the amplification. That requires that the damping factor is reasonably low.

author: KMoffett
author_rank: Regular Contributor
timestamp: October 25, 2020, 07:30:01 pm
content: Quote from: Gyro on October 25, 2020, 05:39:40 pmBack in the day, when I started working in a hospital, the American Optical cardiac monitors user meter relays to display heart rate and set upper and lower alarm limits.

author: akimpowerscr
author_rank: Regular Contributor
timestamp: October 25, 2020, 08:23:55 pm
content: Punched tape or perforated paper tape is a form of data storage that consists of a long strip of paper in which holes are punched.This seems to be the only possible solution.It has been used in the past:https://en.wikipedia.org/wiki/Harvard_Mark_I"The Mark I read its instructions from a 24-channel punched paper tape."How it works :https://iclces.uk/articles/reading_punched_paper_tape.html

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: October 25, 2020, 08:27:18 pm
content: Highly impractical, but lamps and various photocells and photographic film all existed way back. You could store a digital sequence on a strip of film using a motor and lamp. You could read it back in using a selenium or copper oxide(?) cell. A carbon microphone capsule is capable of modulating a fairly large current, maybe enough for a very small relay, so maybe you could make a wax cylinder memory system with a driven tuning fork input and direct reading capsule output. There are various weird but possible solutions.

author: vk6zgo
author_rank: Super Contributor
timestamp: October 25, 2020, 11:19:59 pm
content: Meters which would trip switches at given readings were fairly common back in the day.Mostly the movement didn't have to supply the force to operate the contacts, but simply tripped a pre- tensioned switchFrom memory, with ones like that, the switches had to be reset after operation.

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 26, 2020, 05:07:50 am
content: Quote from: vk6zgo on October 25, 2020, 11:19:59 pmThinking about it, you could use a crystal radio earpiece (extremely sensitive) to bounce a laser beam such that a signal would wiggle it enough to trip a sensor. A bit of a kludge but theoretically possible to make work. Not sure how you would build a laser without solid state electronics, perhaps helium neon with a tube rectifier and a mains frequency neon sign transformer?Since that still needs tubes, it goes back to the tube amp as the straightforward answer. Practical tube amps predate practical relay computers by a few decades so it wouldn't be out of place at all.

author: Berni
author_rank: Super Contributor
timestamp: October 26, 2020, 05:17:36 am
content: Ben did an excellent video on a specialty low current relay:It is basically a sensitive analog current meter that touches its needle onto contacts.

author: Ian.M
author_rank: Super Contributor
timestamp: October 26, 2020, 06:33:26 am
content: It may be possible to get enough energy at a high enough frequency from a tape head to drive acoherer detector, which would be easily capable of driving a sensitive relay. Add a tapper to decohere it, with sufficient actuator delay to get a long enough output pulse and encode '1', '0' and framing as delays between pulses and an entirely electro-mechanical magnetic tape reader may well be possible. The matching writer would be a tuning fork, solonoid + carbon granule microphone oscillator, switched to the tape head by a relay to generate record each pulse, probably with a permanent magnet erase head.See:https://hackaday.com/2017/02/01/early-electromechanical-circuits/#more-241521for more details of coherer operation and a link to a modern implementation.

author: jonpaul
author_rank: Super Contributor
timestamp: October 26, 2020, 06:59:16 am
content: LondonNight: BRAVO for your efforts!You are in the footsteps of many historic efforts:Konrad Zuse, 1936..1937, Z1 relay computer.https://en.wikipedia.org/wiki/Z1_(computer)Mechanical Babbage engine of 1890s.https://en.wikipedia.org/wiki/Difference_engineBack to the first punch hole uses, see player pianos and the Jacquard Automatic Loom:https://en.wikipedia.org/wiki/Jacquard_machineFor storage most early mechanincal and electromechanical machines used punched tape like 5 hole Baudot (TTY) or "IBM cards" (Hollerith)The WWII Colossus decoder of Lorentz was rebuilt by Anthony SALE, at Bletchley Park: Used high speed paper Baudot tape read by photocellshttps://www.codesandciphers.org.uk/lorenz/rebuild.htmThe other posters propose many complex solution but if the core issue us data storage, the holes in paper are hard to beat.Enjoy and Bon Chance!Jon

author: Ian.M
author_rank: Super Contributor
timestamp: October 26, 2020, 08:02:07 am
content: The problem with a punched tape reader is sourcing suitable tape pre-punched with sprocket holes. You *may* be able to source some NOS, but its become vanishingly rare. If you are building the tape reader and punch from scratch, and don't need byte-wide data, it may be possible to use flat paper SMD carrier tape, or it may be possible to build a punch that punches the sprocket holes as well, before the tape reaches the sprocket, so you can use plain tape feedstock.If you are building the tape punch and reader from scratch, there's also the mechanism complexity to consider - the actual punch will need a precision machined anvil, well controlled actuator travel (to avoid hanging chads), and precision ground and hardened punch bits with coaxial stripper pins. A purely electromechanical reader that doesn't wear the edges of the punched holes is also fairly challenging as mercury pool contacts are no longer acceptable - possibly a rotating drum of pogo pins driven by the sprocket holes could work. If you don't have access to a *good* machine shop and the experience to use the machine tools effectively you are SOL as the materials, complexity and precision required are well beyond the practical limits reasonably achievable with hand tools and a hobby 3D printer.

author: geggi1
author_rank: Frequent Contributor
timestamp: October 26, 2020, 08:23:04 am
content: If you are going to have an mechanical computer you should go all the way.In the old days punched paper tape or cards where used for storing data and programs.Go looking for a old mechanical Telex (RTTY) machine with tape puncher.https://en.wikipedia.org/wiki/TelexYou will be able to write the instructions on the TTY machine tape and also use the machine to input the instructions to the computer.For testing you might be able to use a PC to upload the instructions to the computer by seril or paralell port and some hamradio RTTY software.

author: LondonNight
author_rank: Contributor
timestamp: October 26, 2020, 09:36:14 am
content: Quote from: NiHaoMike on October 25, 2020, 05:52:41 pmTubes are not allowed. Everything must be electromechanical/magnetic/etc.

author: LondonNight
author_rank: Contributor
timestamp: October 26, 2020, 09:37:24 am
content: Quote from: SilverSolder on October 25, 2020, 06:05:21 pmAs I said, solid state technology is not allowed. All must be done using electromechanical/magnetic means.

author: LondonNight
author_rank: Contributor
timestamp: October 26, 2020, 09:39:28 am
content: Quote from: Twoflower on October 25, 2020, 06:13:03 pmThis is a pretty interesting idea, I'm writing it on my list here!

author: BrianHG
author_rank: Super Contributor
timestamp: October 26, 2020, 10:14:00 am
content: Since VHS tape is cheap and you mentioned it. Look into the mechanics of a tape head and create one which is a vertical head the full height of the tape.To do this, look ijnto 3D printed ferro filament to replicate the structure. In other words, a 1 inch tall head with with a 0.01 inch or smaller focus gap. You will need to wind your own magnet wire onto the 3D printed U shape.Better solution here:https://www.eevblog.com/forum/projects/electromechanical-way-of-detecting-ultra-low-currents/msg3296438/#msg3296438regardless of no longer needing to 3D print, the recording specs are still valid.You will want 2 heads with 2 different gaps, 1 for read, 1 for write. Expect the tape to run fast at around 10-25 feet per minute to generate a sharp transition edge from the VLF 15 - 30 baud which you might achieve.The read head will have many more turns of a finer magnet wire and you are targeting (praying for) around +/- 1ma, but with such a huge ass head an tape speed, I bet you can get 0.1ma pulses easily, enough to just be heard by headphones without an amp, just enough to trigger a 2 pole position reed relay because of the huge 1 inch tape height and tape speed with a 100% saturated magnetic field in it. (Stamped/cut iron would give you ~6x signal strength, but the 3D printing is a way to measure and test the possibility and refine the shape.)See 3D printer compatible ferro filament in action here @3:55:When writing, you will need to drive the head with a relay driving the heat with around 1 amp of current AC, meaning not 60hz, but 1 polarity to write a 1 and another polarity for -1. This is easily done with a single DPDT relay (I expect a dirty 10hz max), or, much better and with 2 batteries, for a +&- DC power supply, a SPDT reed relay (Common to write head, + & - DC to each pole)(mercury-wetted, 1 amp at 30hz will burn out most other types plus there wont be any contact bounce in the write signal), will generate clean write signal up to 30 bps. Faster than the rest of your system, but fast enough for the read head to get a good voltage and current on the playback.So long as you are allowed to use reed relays. The illustrated meter above proves it is technically feasible for you to receive a polarized 0.1ma signal and have it fire off larger polarized reed relays (SP3T, NO, or +1/-1) to amplify the signal to a usable state.All this does is tell you how to record a serial bit stream and play it back. You may cheat a tape mechanism through vandalizing a VCR, but the current heads and capstan system will be useless and too slow. Once the tape is loaded, you will also need to tension the tape across the 2 heads, but with all the VHS deck pulleys available at scrap electron yards, you might be able to put something together.The tape mechanism is a project all on it's own, but, just getting a 30Hz square wave in and out through relays without any electronic amps using 3D Printed tape heads and old T120 VHS tapes would give you legitimate bragging rights all on it's own.Document every step of the R&D process. No one will believe you it you get that tape mechanism working.Making that run a relay computer as well would be something to see.

author: Haenk
author_rank: Super Contributor
timestamp: October 26, 2020, 10:30:22 am
content: I'd use a vintage (electromechanical) teletypewriter for the reader and writer parts. This is actually how the early computers, or at least Zuse, did with his relay computer. A roll of teletyping paper is available on ebay Germany for very little money, complete teletypewriters are not too expensive either.This is a solution that has been used for more than 50 years. Why reinvent the wheel...

author: BrianHG
author_rank: Super Contributor
timestamp: October 26, 2020, 10:48:30 am
content: Quote from: Haenk on October 26, 2020, 10:30:22 amBase on what the OP asked, I get the feeling he wants to create something unique.With 2 motors on a tape deck, fast forward, and reverse/seek becomes possible as well as a few kilobytes of data to access. It's like he wants to make a relay supercomputer.at 30Hz well tuned, maybe even with the capscan motor running the tape at almost 10m/min, he can do quite a bit more like a tape serial based RAM memory.Try making system computer re-writable ram from a spinning circle of of punched paper. How do you fill back in the holes?

author: BrianHG
author_rank: Super Contributor
timestamp: October 26, 2020, 11:15:39 am
content: @LondonNight, if you will be using a separate tape system for storage and another circular loop for cpu register ram, you might as well add a video display controller by buying a grid of BINA-VIEW full character display elements.

author: Haenk
author_rank: Super Contributor
timestamp: October 26, 2020, 11:24:39 am
content: Quote from: BrianHG on October 26, 2020, 10:48:30 amMaybe some very clever people already had this idea thrown out 80 years ago and went for: relays.A purely mechanic storage can be done - Zuse did it on the Z1 - but my understanding is "electric stuff - yes. electronic stuff - no", so paper strips as data storage (mechanical fingers as reader) and relays as RAM would be perfectly fine, following this concept. Which is just how they did on the earliest computers.The teletyping-stuff is just to ease the operation (inputting programs and data and outputting results). You could still toggle bits by hand, if you like, and read out results on blinking lamps...

author: BrianHG
author_rank: Super Contributor
timestamp: October 26, 2020, 11:40:06 am
content: Quote from: Haenk on October 26, 2020, 11:24:39 amYup, I know, relays are perfectly fine. Register file of 256bytes would be a nice 65k relays, um, well, maybe a 64 bytes for registers making that 512 relays. That's fine. (I'm thinking of a complete system which can completely fit on 1 large table.)What if you want to store and double or triple process/edit a 2k table of data a number of times.1 thing I do agree about the punch-hole tape is you can make an all mechanical type-writer program entry system and visually inspect the tape.Unless the OP is trying to recreate something that has already existed in the past and maybe just add a little new peripheral, I think restricting himself to electro-mechanical and dreaming up something new and weird with quasi new materials for a project which can go one for over a year is something of a goal to achieve.

author: BrianHG
author_rank: Super Contributor
timestamp: October 26, 2020, 12:22:20 pm
content: I'm so stupid... @30hz, tuning the tape speed, the existing erase tape head which is already in the VCR mechanism may already be perfect... Just place 2 identical ones apart from each other and improve the tape tensioning on them with pulleys and see what kind of return signal you get by running the tape at different speeds feeding a 30Hz square wave @ higher than normal currents... (I have made nice 30hz square waves with reed relays before, so I know this is a good metric for bitrate. I also know many mercury wetted relays are 1 amp capable unless you want the really rare more expensive ones.)The erase head is already a vertical head, 1 track the full width of the tape. Though, it is not optimized for playback. Maybe salvage a few different VCR erase heads and experiment with 1 VCR deck playing back a tape at 10x speed seek mode. Using a scope and function generator which can drive an amplified output for the write, you can see in real time as the moving tape passes the record eraser to the next head if you get any meaningful current from the adjacent playback head with a mechanical ma meter or headphones tied to it's 2 terminals. (15-30 Hz should wiggle the meter visibly if strong enough. The record head will need a good amount of current to really magnetize the tape, but, you do not want to burn it out.)Easy test with any VCR you do not care about which will play blank tapes...Vertical alignment angle of the head you place will determine the quality/strength of the playback signal.Unfortunately, for playback, you would want much higher coil turns and for record, you would want fewer, lower gauge for high current magnetization. If yo get any unamplified signal at all, maybe a impedance matching line transformer can boost up the signal level. Some old mike pre-amp-less audio transformers exist with a 10:1 and 20:1 gain which go down to the 30Hz range, especially since you are recording a square wave which may be seen as 60 pulses a second in the 60hz band with alternating polarity.If you are willing to spend $ on a studio mic transformers, 40:1 and 100:1 exist with bandwidths down to 25hz, but, the output current must be like a flea coming from a tape head.

author: akimpowerscr
author_rank: Regular Contributor
timestamp: October 26, 2020, 01:15:03 pm
content: The signal level of a magnetic head is only a few mV's and the resistance of the windings is high.Such a signal cannot be used in a purely electro-mechanical system without amplification.The magnetic tape solution is therefore obviously inapplicable for the use in question.

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 26, 2020, 01:36:05 pm
content: Quote from: akimpowerscr on October 26, 2020, 01:15:03 pmA crystal radio earpiece will respond to that just fine. Might be worth trying that with a diode laser and photoresistor to determine how feasible the idea is, then find some alternative to the diode laser. Maybe a focused halogen or HID lamp will work.

author: LondonNight
author_rank: Contributor
timestamp: October 26, 2020, 01:40:18 pm
content: Quote from: akimpowerscr on October 26, 2020, 01:15:03 pmI have seen a reply on this post of an electromechanical device capable of reacting to signals as low as 2.5uA, this whole deal begins to feel possible. The solution may not be straightforward, but there must be some solution.

author: LondonNight
author_rank: Contributor
timestamp: October 26, 2020, 01:41:40 pm
content: Quote from: SilverSolder on October 25, 2020, 06:05:21 pmNo diodes allowed

author: LondonNight
author_rank: Contributor
timestamp: October 26, 2020, 01:43:04 pm
content: Quote from: akimpowerscr on October 25, 2020, 08:23:55 pmI agree, but as it has been said by others here, you can't fill the holes in a paper tape, to 'erase" it.

author: BrianHG
author_rank: Super Contributor
timestamp: October 26, 2020, 01:44:26 pm
content: Quote from: akimpowerscr on October 26, 2020, 01:15:03 pmThe head we are talking about is 1 inch tall. Not sub-millimeter tall, IE 1 track.It has something like 50 windings on each side., not 5-10 line a normal tape head.[--] IE That center inside the -- is something like a single track head in normal tape players. It is a thin strip of metal shaped like a horse-shoe magnet a fraction of a millimeter high. Usually more than 1 of these for stereo.[][] This is the type of head he will be using on the VHS tape. It is the same type of horse-shoe type magnet shape, except, instead of being less than a millimeter thick, that metal electromagnet is 1 inch tall with a thick many many turn coil with enough current to erase/degause with a good injected AC waveform for entire vertical 1 inch surface of the video tape, not record a sub-millimeter wide track.Now, if we move the tape a litter faster than normal and record a 1 inch vertical track with a square wave approaching 1 amp instead of the original 100-250ma degause signal.During playback, please tell me how much more playback signal current will we see on a 1 inch thick track compared to the signal strength you describe of a few mV's. I'll give you a hint, the low current few mV's at normal playback speed vertical signal area is ~25 times smaller than the full vertical write size of the tape. Hmmm, 25:1 there. We will run the tape at 10x speed. That helps. We will also be using a + to - 100% saturated 30Hz square wave exclusively as it is digital. Hmmm, it's still a long shot, but I bet the test will make enough of a playback signal to exceed 0.3v with 0.6v spikes during the square wave transition. That's enough to directly drive an electromechanical watch coil, no transformer needed. Enough to be relay amplified.Have you seen the thickness of the coil in a VCR erase head? It's actually exposed on some units as it openly goes to solder posts at the top of it since it's thick enough, no sensitive protection necessary. It's actually a little thicker than the voice coil inside my PC's internal speaker.

author: LondonNight
author_rank: Contributor
timestamp: October 26, 2020, 01:45:56 pm
content: Quote from: jonpaul on October 26, 2020, 06:59:16 amThe paper tape solution may seem like a good one, but a reader would imply quite serious engineering, at the contacts, since mercury bath contacts are not a thing anymore. Not to mention I would need to get some sort of paper puncher. And at the end of the day, if I want to erase the storage medium, i can't simply fill in the holes in the paper...

author: LondonNight
author_rank: Contributor
timestamp: October 26, 2020, 01:47:11 pm
content: Quote from: Conrad Hoffman on October 25, 2020, 08:27:18 pmAs you say, highly impractical, and the storage medium is one time use only.

author: LondonNight
author_rank: Contributor
timestamp: October 26, 2020, 01:47:42 pm
content: Quote from: vk6zgo on October 25, 2020, 11:19:59 pmYou may be onto something!

author: LondonNight
author_rank: Contributor
timestamp: October 26, 2020, 01:51:55 pm
content: May I ask where you came up with all those numbers from? Just asking

author: LondonNight
author_rank: Contributor
timestamp: October 26, 2020, 01:54:16 pm
content: My relay computer features 256B of RAM memory made from capacitors, so the RAM is settled. What I need is a long term storage medium for pre-made programs, so when I need to run a certain program, I grab a cassette and play it, loading all the data into RAM. From there, the computer will run the program from RAM.

author: LondonNight
author_rank: Contributor
timestamp: October 26, 2020, 01:56:27 pm
content: I wouldn't be able to detect the light, since photodiodes/photo detector tubes are not allowed...

author: akimpowerscr
author_rank: Regular Contributor
timestamp: October 26, 2020, 02:22:20 pm
content: QuoteWhy erase?It is still not that difficult to create a simple machine that makes cheap paper tape from rolls of suitable paper.We used to make a lot of paper tapes back then, why not make any more today.It seems to me that you want to create unnecessary obstacles.The magnetic tape solution also encounters other difficulties:- a purely electromagnetic system, and especially if it works with very small signals, is very slow. It takes at least 10 ms for the relay to actuate and latch.Pulses of at least 30ms are therefore required for reliable operation.- Even if you record a signal of a 30ms pulse, you will not have the same signal at the output of the magnetic read head, the amplitude indeed decreases at the end of the pulse.You should have a Hall based read head to reproduce long pulses.- On the other hand, there is the problem of the time required between each pulse for the electro-mechanical device to be reset to 0 and ready to read new informations .... It takes several hundred ms .... You you will therefore need a long length of magnetic tape to store little information.- With a magnetic read head, you cannot decrease the speed of the magnetic tape excessively because the output level of the signal will decrease even further.- if you choose a sequential and non-continuous scrolling of the tape, there will be the problem of the perfect positioning of the tape, problem which is solved mechanically in the paper tape drive.

author: Berni
author_rank: Super Contributor
timestamp: October 26, 2020, 02:25:34 pm
content: There are ways of amplifying signals using magnetics. If you make a transformer with an easily saturable core material you can add a 3rd winding to bring the core in and out of saturation to control the amplitude of the output signal. If the 1uA signal to drive that sensitrol relay is too much to get from a tape head, possibly such a magnetical amplifier could boost it.But I don't see why detecting light would be a foul. You can make LDRs by simply coating the right material(Such as CdS) between two electrodes, no actual proper semiconductors or photodetector tubes needed. Tho the down side is that LDRs are really slow, so gettting a good bitrate out of one might be dificult.

author: BrianHG
author_rank: Super Contributor
timestamp: October 26, 2020, 02:42:58 pm
content: Quote from: LondonNight on October 26, 2020, 01:51:55 pmWho are you asking?And which numbers.I have made 1 mistake, VHS tape is 0.5 inches tall, not 1 inch tall.According to Wiki, an audio cassette has a record track width of 0.6mm max, A playback head is usually a little thinner, let's call this 0.5mm. VHS (used our custom way) would be 25mm (1/2 inch). Since we are using the full vertical for record and playback, we have a playback magnetic vertical surface 50 times higher than an audio cassette. An audio tape also has a tiny 1.2 micrometer gap to pick up that tiny high frequency transition at slow speed. As @akimpowerscr mentioned, a playback from an audio tape head is only a few mV and is super weak with the dimensions of that head.The VHS erase head looks more like a thing vertical fat magnet to the tape. Since it is designed to degause a tape completely of old recordings at 50x times over the vertical surface area, and, also does so much thicker than 1.2 micrometers wide as you cannot construct 50mm tall head with an accurate 1.2 micrometer gap, this is also has become much wider (not a standard bu at least ~100x the horizontal). Speeding up the tape will also help cover this horizontal area fast enough to make a recorded 30Hz signal appear really sharp. During playback, a higher speed also produces a larger signal across the head when used for playback.Like I said, putting these factors together will generate a signal orders of magnitude more powerful than an audio tape playback head. This means more voltage and more current. I do not know how far this can be stretched. I do not know how much current you will get, but it still is small, but wont be in the few mV sub micro amps like audio cassette tape playback.I used to repair VCRs and I know what the erase heads look like and some even had visible open backs as they were nothing more than a high frequency electromagnet to degause the tape. See the illustration of a vhs player below, see the full erase head, in almost all units, it only has 2 pins. Get a VHS machine, put in a tape, press play with that head disconnected. Tie it to a function generator with +/-15v out (NOT 0-15v, -15v to +15v), 10-30Hz square wave with the tape playing in FF 10 seek mode. (Speed may go haywire as you erase the tape and the VCR electronics cannot determine the tape speed (SP/EP).) After a minute, stop, rewind, place scope on 2 pins and playback at 10x seek again and see if you get anything. If you can see a spikey signal with spikes above 100mv (might already be strong enough to hear a buzz on headphones wired directly to those to pins), you have passed 1 barrier. Now you will need to up the record current to the head's limit. This part may damage the erase head, but, your testing will need to determine the safe operating voltage and current limits of the head.As for the ~30Hz, I know limit from trying to make a relay based inverter in the late 70's using relays. 60 Hz was almost doable, but not stable unless I used mercury wetted relays. 30 Hz was fairly good and consistent. Reed relays are far faster than the large mechanical ones I was using, so this figure is an estimate.As you can see, may be a long shot, but, passing barrier #1 above can be done without damaging any VCR, all you need is a working one and some basic lab gear and a day of playing. Testing the maximum will definitely grow that 100mv unless your function generator can already put out a good 2-5 watts of power. Trying different tape speeds may also improve results.(Playback would look like up & down spikes since the head's coil isn't tuned to operate down at 30 Hz)

author: jonpaul
author_rank: Super Contributor
timestamp: October 26, 2020, 02:44:32 pm
content: Baudot tapes: Look for Teletype 33ASR or similar TTY teletype terminalhttps://en.wikipedia.org/wiki/Teletype_CorporationElectromechanical and perfect!Jon

author: akimpowerscr
author_rank: Regular Contributor
timestamp: October 26, 2020, 03:25:43 pm
content: Teletype SIEMENS T100 full manual with tape reader attachment.http://www.vmarsmanuals.co.uk/new/t100.htm

author: LondonNight
author_rank: Contributor
timestamp: October 26, 2020, 03:37:56 pm
content: I really don't know what to say to that. The problem has been presented, and I came asking for help on solving the problem, not on changing the problem... IF what I need proves to be impossible to do, then I will resort to using paper tape, but until then, let's all think about what could be done with the current situation, and the current situation dictates that I have to use magnetic tape.Sidenote: As I have stated before when talking to other members, working with paper tape is a pain in the ass by itself, both writing and reading from the paper tape. Also, VHS tapes/Audio cassette tapes already conveniently come in a plastic case, so I don't have to actually touch the tape itself. As for paper tape, I would have to buy paper tape, and each time I would want to load a program, I would have to manually insert the tape strip itself into the machine, and who knows how I would get it to rewind to the beginning after I'm done with it... It's not as easy as it sounds once you actually try it... (spooling the paper tape from reel to reel)

author: LondonNight
author_rank: Contributor
timestamp: October 26, 2020, 03:43:00 pm
content: I have one question, regarding all this. Why specifically 30Hz square wave? Why wouldn't sine wave work better?

author: LondonNight
author_rank: Contributor
timestamp: October 26, 2020, 03:44:51 pm
content: Quote from: jonpaul on October 26, 2020, 02:44:32 pmAs I have stated in my original post, I want to use magnetic tape for this job.

author: BrianHG
author_rank: Super Contributor
timestamp: October 26, 2020, 03:44:56 pm
content: How about magnetic wire recording:https://en.wikipedia.org/wiki/Wire_recordingIf you have a strong solenoid magnet, or rare earth magnet charging a pattern onto one, I bet you might find a magnetic reed switch sensitive enough to playback that wire signal just by proximity, or even cut into the reed relay glass so that that wire feeds as close as possible to the reed switch. No tape head... Record head would just be a busted open relay magnet rubbing above the wire.They had such record power, it was invented before and functional before the vacuum tube in 1898.Still available EG:https://www.ebay.com/itm/Silvertone-RECORDING-WIRE-3-Spools-Stainless-Sears-Roebuck-2-tins-Vintage/174486709140?hash=item28a037e394:g:aHcAAOSwyR1d-TJbJust search for a heavy gauge and it will be able to be charged enough for the reed switch, or, your own home made switch.

author: LondonNight
author_rank: Contributor
timestamp: October 26, 2020, 03:49:58 pm
content: Quote from: BrianHG on October 26, 2020, 03:44:56 pmThat's another great idea! I will definitely look into it.

author: BrianHG
author_rank: Super Contributor
timestamp: October 26, 2020, 03:51:52 pm
content: Quote from: LondonNight on October 26, 2020, 03:49:58 pmThey had such record strength, it was invented before and functional before the vacuum tube in 1898, recording telephone audio and playback direct to headphones. Though, the wire was much thicker back then.

author: BrianHG
author_rank: Super Contributor
timestamp: October 26, 2020, 03:59:08 pm
content: If clean enough, run 10 magnetic wires in parallel, 1 for clock and 8 for data and 1 aux for addressing begin and end program and aux functions, giving you parallel loading and saving of 1 byte at a time. Imagine 30 cps, or 300 baud. Your relay computer would be at 8bit home computer tape/modem speeds.

author: LondonNight
author_rank: Contributor
timestamp: October 26, 2020, 04:10:21 pm
content: Quote from: BrianHG on October 26, 2020, 11:15:39 amWould be quite spectacular to see that, but unfortunately, they're not for sale anywhere...

author: BrianHG
author_rank: Super Contributor
timestamp: October 26, 2020, 04:48:40 pm
content: Quote from: LondonNight on October 26, 2020, 04:10:21 pmToo rare and expensive to manufacture,Just youtube search BINA-VIEW, their is a guy who design and built his own with online design files. Though, with a little better modern available manufacturing of the film parts and sourcing a good lens for the back light, you can build your own.Here is Fran doing a repair of here unit, see inside and how it works:It is nothing more than a latching relay circuit with slides which have a binary bit pattern at their bottom edges, so the 5 bits on the 5 relay lengthened arms selects 1 single slide like a key which will allow it to be dropped and viewed. The a final relay arm to reset / lift all the slides out of place.Google BINA-VIEW schematics/diagrams. They may exist.If it weren't for the lamp heat, you could probably 3D print the majority of this device except for the relay coils, arms, lamp and lamp culminating lens. Actually, 3D print using optical UV 3D printers and they wont melt plus you may get those razor thin letter cells. They are so thin, so little fluid used, it might not cost that much. Laser stencil cutting of thin sheet metal/tin also exists today giving you perfect letter cells as well as the 6 bit relay arms that shift left and right. Probably cheaper than 3D printing. You have the money, and someone can replicate this unit for you cheaper than it would cost to buy originals if they were available anywhere.I wonder if laser cut films may be used for the plates. Those would be thinner and lighter while the springs above wouldn't need to be as strong or ever there due to lack of friction.You would obviously code for ASCII, or closer to it with 64 characters available.(Hence my comment, if price is no object... meaning you would need to get someone to engineer and build these for you.)

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 27, 2020, 12:33:37 am
content: Hmmmm, I wonder if you can get print + electrochemically etched sheetmetal pieces at rapid-prototype prices/quantities, like you can 3D prints and PCBs and such. Surely it's a small market, but seems like something eminently available these days.Tim

author: BrianHG
author_rank: Super Contributor
timestamp: October 27, 2020, 02:12:04 am
content: Quote from: T3sl4co1l on October 27, 2020, 12:33:37 amI had a little time to think it through.Laser cut sheet metal, IE each letter with that 'honey comb' structure with thin metal like that of tin cans, half thickness, like that of soda can aluminum, or even made of aluminum itself would be great for the letters / screens as well at the top support spring plate structure holding down all the letters.The letter cells could be anodized black.For the bottom base structure which holds the letter cells, supports the lamps, contains 3 long vertical fins with axels on the left and right providing the 6 bit selectors plus 7 relay vertical clear which raises all letter cells should be printed in one of those new 350$ UV cure optical 3D printers. The resulting print is firm, non flexing like plastic filament prints, always really repeatable sizes & once UV cured, the heat from the supported incandescent lamp wont melt, soften or deform this structure like plastic.+ Bonus on these 3D printers, (I bet you didn't know this one), they have optical transparent epoxy designed for printing actual lens in the printers. Yes, you can also print that lens for focusing the light culminating lamp which would be otherwise hard to source in the shape and size needed for a BINA-VIEW character display.All you need to mount internally are wire harness, lamp socket, 7 relay coil cores, flap metal slabs or clips, IE top lever of relays to the 6 bit 3D printer levers + 1 big on for the thick clear lever which may have 2-3 relay coils in parallel for enough strength to lift the letters.If I had to, I would invest in a second level tier 600-800$ optical printer to print the BINA-VIEW chassis and lamp optical lens. (Optical epoxy is more brittle, so use 2 different prints.) Simulate and print everything in Fusion 360 first, including optical lens focus and letter cells. Then, once everything mechanically works, since the optical epoxy is clear and a little too brittle for repeated impact and cant produce the top spring (well it can make the structure, but it wont bend), take the cad of the letter cells/top spring and get a metal shop to laser cut them and anodize the letters black to finish my displays.Build a reasonable 80 of these units today like this and even with cost of the 3D printer and UV epoxy and cad tools + set metal shop costs, it would still cost less than buying the original 80 units. There is still a chance you can make the letter cells in the 3D optical printer 2 of 3 layers thick each and find a thin enough paint which will stick to make usable letters as well, but, you would still need to do something about the top support pressure support springs as gravity is not reliable here for transport and friction issues.

author: BrianHG
author_rank: Super Contributor
timestamp: October 27, 2020, 02:30:15 am
content: 1.3K$ precision Laser printer I would like (a toy) :https://peopoly.net/products/moaiMarco Reps got a sponsored one here where he 3D prints an optical lens:https://youtu.be/OoVvQids1DA?t=739Not sure how much he payed, but I'm sure he got a deal (hint to OP) since he made a video about it.Make no mistake, to get a long term BINA-VIEW engineered for 3D printing, you need an engineer in the field who know what they are doing.The base may be still done by CNC machined aluminum instead.A transparent 3D printed lens still needs polishing after it is printed, otherwise it will have a frosted surface, which also may be usable as a cell inside the BINA-VIEW to smooth the light source behind the letters.

author: jonpaul
author_rank: Super Contributor
timestamp: October 27, 2020, 06:41:34 am
content: Hello all:Magnetic tape and wire recorders date back to 1920s..1930s, but the signal in the tape head is in the microvolt range.You require electromechanical solution to read the tape.To my knowledge, all tape recorders require electronics for the amplification and equalization.Try physics simulation of the proposed tape head/tape magnetic circuit to see the expected flux and signals.Jon

author: Ian.M
author_rank: Super Contributor
timestamp: October 27, 2020, 08:42:07 am
content: A magnetic wire recorder was patented in 1900, by Valdemar Poulsen:https://patents.google.com/patent/US661619A/enAs this was four years before John Ambrose Fleming invented the thermionic valve, its obvious that it could not have relied on electronic amplification to function.Amplfication can be achieved by purely electromechanical means, even with very low level input signals. Here's a good introduction to the subject:http://www.douglas-self.com/MUSEUM/COMMS/mechamp/mechamp.htmA possible lineup for a digital electromechanical magnetic tape or wire playback circuit woud be a high output playback head driving an electromechanical amplifier consisting of a solonoid exciting a tuned reed coupled to a pair of carbon capsules in push-pull, with its output feeding a coupling transformer driving a pair of copper oxide rectifiers to provide a DC output to energise a sensitive relay. The relay would thus pull in when there is a burst of tone on the tape or wire of sufficient duration. Encoding '0' and '1' bits could either be done by the tone burst duration and/or spacing, or by FSK, using two amplifiers, each with its reed tuned to a different frequency.With an extra switchable feedback winding on the coupling transformer, the amplifier could be used as a power oscillator to drive the record head. It would probably be preferable to let it oscillate continuously during recording and simply switch its output to the head to form each pulse, (or switch either the '0' or the '1' oscillator to the head if using FSK).Alternatively, a solid state oscillator or even an amplifier using contemporaneous materials and methods is practical. Seehttp://www.sparkbangbuzz.com/els/zincosc-el.htmfor such a device using a home made steel/zinc oxide junction. To develop a practical audio frequency amplifier, I would suggest modulating a RF oscillator and detecting its output, as otherwise its very difficult to prevent feedback when using a two terminal negative resistance device.

author: BrianHG
author_rank: Super Contributor
timestamp: October 27, 2020, 08:57:36 am
content: @jonpaul, magnetic steel wire with a record gap of say 5mm long will have a stored field strong enough to push and pull a reed switch. But, you would only get 1 bit every centimeter of wire. Remember, those microvolts you are talking about have signals with a length of sub-0.01 millimeter long charges on the wire making magnetic charges too weak to physically effect anything but an amplified head. I'm talking about charging 1cm blocks of the wire at 1 N-S magnet, digital N-S, or S-N full strength only, that's a magnet with 1 polarity over 10000x the strength. Pulling this charged/recorded wire right above a cheap compass will be enough for you to visually see the bits go by as it will wiggle the compass. Please stop thinking audio or sound with a few kilohertz bandwidth which would squeeze a thousand bits in 1cm of wire. With 1 bit/Cm, 1 meter of wire will only hold 100 bits of data in my scenario where a recording can be mechanically read and written with a solenoid or relay coil, or even with a small 5mm wide cube neodymium magnet rubbed up against the flipped around every 1cm depending if you are writing a 1 or 0.

author: Ian.M
author_rank: Super Contributor
timestamp: October 27, 2020, 09:04:51 am
content: Yes, any electromechanical digital magnetic wire or tape player is certainly going to have a very low bit rate, irrespective of if it directly plays back baseband signals as BrianHG suggests or uses some sort of modulated toneburst as I have been suggesting.The low bit rate is actually desirable as even a 10 bits/sec input stream would be quite fast for a relay computer.

author: BrianHG
author_rank: Super Contributor
timestamp: October 27, 2020, 09:13:06 am
content: It's too bad the OP cannot use a PCB and everything needs to be hand wired. With modern small latching relays, he could have a non-volatile ram of around 2 kilobytes fitted into a box the size of 2 or 3 full size PC tower cases. Also, he could forget that BINA-VIEW and with a second such case, with same sized relay logic, and a flip-dot display, he could have a full 160x120 graphics display with a 128 font character 40x15 lines of text. We are talking about the capability of making a full function plotting calculator.The processor would require another 2 such additional boxes, 1 being a the CPU core + ALU & PC.Basically, modern binary optimized techniques, but all electromechanical.See here flipdot:https://youtu.be/0ZWSOx-T6lg?t=1164Cheap, available and no lamp, no electronics. 100& electromechanical.

author: BrianHG
author_rank: Super Contributor
timestamp: October 27, 2020, 09:14:33 am
content: Quote from: Ian.M on October 27, 2020, 09:04:51 amNo tone burst, DC +, DC -, just like a differential RS485 signal to increase hysteresis. (hysteresis, the added magic ingredient which will make the data readable with any certainty...) The swap in polarity itself would be manipulated to generate an MFM signal, while incorporating an edge clock at the transitions. Or, wire #10=clock.Make a spool with 9 wires, parallel, 8 bits, 1 bit for aux addressing functions and now you are talking 10 bytes per second...

author: richard.cs
author_rank: Super Contributor
timestamp: October 27, 2020, 10:07:09 am
content: Quote from: T3sl4co1l on October 27, 2020, 12:33:37 amWhen I read this I immediately thought of Tecan who make custom shielding cans by etching and folding sheet.https://www.tecan.co.uk/Then when looking at their website I saw they do SMT stencils, and realised the laser cut stainless stencil process is absolutely perfect for this. Unless I have missed something, a stack of stencils would be quite usable, needing only a chemical blackening process.

author: Ian.M
author_rank: Super Contributor
timestamp: October 27, 2020, 10:12:02 am
content: @BrianHG,I don't think multiple wires would be a good idea due to the difficulty of keeping them in alignment. Serial data, with a uniselector for serial to parallel conversion would be far more practical.

author: BrianHG
author_rank: Super Contributor
timestamp: October 27, 2020, 10:15:05 am
content: Quote from: richard.cs on October 27, 2020, 10:07:09 amBrilliantAgain, stupid me. Why didn't I think of that. All the cheap Chinese pcb board places like PCBWay make perfect laser-cut SMT stencils from gerber drawings, which can be converted from any CAD .dxf source file. You can get all your BINA-VIEW letters on 1 printed sheet with resolution printed down to tiny sizes. Dirt cheap on 1 large stencil with cutt-aways for each letter. We are talking accuracy down to 0.0001 inch resolution...This includes printing the 6 bit vertical lever arm blades below the letters all on 1 SMT stencil sheet for 1 complete BINA-VIEW module, only for 5-10$. You'll get a sheet with all the letters plus 4 side cutaway bites to remove the letters from the main sheet. Once confirmed, I bet you can get a bulk deal on quantity.Again, the stainless steel makes for perfect springs on top of the letters, however, make sure you get the thinnest stencils available as the thick ones will need a really strong magnet to reset/push up the active letter.Or, better play it safe, get the cheapest thickness for the letters so they have a bit of sturdiness to them (IE thick enough so they wont warp under the spring messing up the display), and the thinnest stuff for the top sprint structure.

author: cbutlera
author_rank: Regular Contributor
timestamp: October 27, 2020, 12:55:12 pm
content: How about using a small motor-generator as an amplifier for the output of the magnetic head (the generator field is the input), as used in a Ward-Leonard control system, except on a much smaller scale. Or perhaps building a small amplidyne, which is a modified generator that can achieve power gains of 10,000 or more. These were commonly used to amplify watts into tens of kilowatts at sub-audio frequencies. I am no expert and don't know how well this would scale down, but it may provide some food for thought. I expect that residual magnetisation would be one of the main obstacles. Amplidynes sometimes include a small permanent magnet AC "killer generator" to drive a demagnetising winding to alleviate this.I read about these as a youngster in the late 1960s, in a wonderful series of books my dad bought for me called "The New Model Illustrated Course of Elementary Technician Training" originally developed for the U.S. Navy by Van Valkenburgh, Nooger & Neville, Inc. The volume that covered this was "Basic Synchros & Servomechanisms" part two. I still have the complete 21 volume set.

author: BrianHG
author_rank: Super Contributor
timestamp: October 27, 2020, 01:52:04 pm
content: Quote from: cbutlera on October 27, 2020, 12:55:12 pmWouldn't even need to be big. Something like a minuscule toy race-track car motor spinning a second one without it's magnets with the edge up against the moving recorded steel wire amplifying that tiny magnet into a high DC voltage as a playback head itself resulting in a DC output strong enough to drive a reed relay.Basically, rapidly spinning the playback head up against the wire would generate a magnified AC output from that playback head coil. Then feed that amplified signal into an AC input relay.

author: SilverSolder
author_rank: Super Contributor
timestamp: October 27, 2020, 04:18:57 pm
content: Quote from: cbutlera on October 27, 2020, 12:55:12 pmThis is interesting, I never knew that this principle could work as an amplifier... - Maybe a new way to make a power amplifier for your car out of an old alternator?

author: LondonNight
author_rank: Contributor
timestamp: October 27, 2020, 05:05:01 pm
content: Quote from: cbutlera on October 27, 2020, 12:55:12 pmThis is a genius idea! It really seems like something that could pretty much do the job! Your idea is now at the top of my list!

author: LondonNight
author_rank: Contributor
timestamp: October 27, 2020, 05:07:32 pm
content: Please do not deviate from the topic. It is in the rules

author: Gregg
author_rank: Super Contributor
timestamp: October 27, 2020, 07:21:41 pm
content: This may be of interest: Jeri Ellsworth discussing magnetic logic gates

author: akimpowerscr
author_rank: Regular Contributor
timestamp: October 27, 2020, 07:50:07 pm
content: Many Russian operating machines used amplidynes (rotary amplifiers) to control the speed of direct current motors.We modernized these machines by replacing these amplidynes with thyristor speed variators because these amplidynes required a lot of maintenance and often broke down.I have documentation in French on this subject, I can scan it and post it but it is about ten pages.As for coming to argue that this principle can be used with signals of a few mV's, it is totally ridiculous.Wanting to build a super miniature amplidyne for this purpose is totally beyond the reach of the technical and financial means available by LondonNight

author: BrianHG
author_rank: Super Contributor
timestamp: October 28, 2020, 12:06:35 am
content: I'm not sure what I would like better, using a super expensive BINA-VIEW text display and spend my time engineering those, or, use the magnetic flip-dot display and and spend the time on a relay XY address decode plotter to have a graphic display so your relay PC can play a slow-motion game of pong via software as well as a simple drawing paint program, not to mention text.Magnetic flip-dots are easy to get, but, you need more relay logic or rotary cam logic computers to get text working efficiently.Also, don't forget 7-14 scale tuned bells + 1 drum and 1 high-hat so your computer can play music software.Maybe make a Tetris game running at 1 frame per second.I may be wrong, but I am assuming you are targeting a generic 8 bit CPU with 1k. This is doable executing 2-4 instructions a second with really small 2 coil S-R relays.

author: BrianHG
author_rank: Super Contributor
timestamp: October 28, 2020, 03:51:32 am
content: Just watched your video.Using SR relays would run computer ram and core static, no cap ram, remember forever, only consuming a small amount of current for processing during a clock transition.Using bottom end 4PDT 2 coil SR, or 1 coil, 2 polarity relays would have made the ALU and PC & ram fetch process run at a good 2-5 instructions per second. Your first 10 Fibonacci sequence would have been calculated in around 30 seconds compared to your existing design. If you designed a Harvard architecture cpu, maybe something like 5-10 seconds. The available through-hole relays only consume 10ma and switch in under 3ms. This is low enough power for wirewrap wire. Yes, an 8bit binary add/subtract should only take 10ms (assuming 2 layer deep relay gates). Depending on the number of additional relays, status flags Z B C can be done in parallel, or, take another 3ms.(Caveat: I do realize you are attempting to use minimal relays and instructions. My design approach would be to have a dedicated adder card, dedicated and, or, xor logic card's, in fact, 1 card per op-code instruction when when an op code is read, all the cards wired in parallel, 1 board would be selected to enable it's outputs. Also, the Harvard architecture has 3 separate buses allowing for data register ram and an instruction rom/ram plus the W work register. So control for the ALU opcode and data ram to compute with the W work register are all available in parallel meaning 1 clock to complete a complete instruction & by the next clock, the next instruction. Hence, with 3ms relays, even 10 operations per second might even be possible with a relay CPU wired this way.) I figured without this explanation, you would think I was mad, but, I basing my design on an old PIC16C54 which I have written an equivilant in HDL (basically making one with gates) from scratch. It would be nice to see a relay computer run C or ASM compiled code from a modern MCU compiler.The relays I would use are 9x14mm, 5mm tall. Stacking cards on an edge-board connector, the back-plane of this system would be ~100mm wide for 15 function boards for the Program counter with 4 level deep hardware stack (supports goto, call, return, indirect addressing & interrupt input), 12 ALU boards for 12 functions, 1 W board & C,DC,Z flags, 1 branch test board.2 other similar boxes for the ram and program memory. (Using 1/4 sized relays SPST)

author: LondonNight
author_rank: Contributor
timestamp: October 28, 2020, 06:02:55 am
content: Quote from: akimpowerscr on October 27, 2020, 07:50:07 pmDoesn't mean it can't be tried. Also, the amplidyne will be small, but not so small that it can't be built.

author: LondonNight
author_rank: Contributor
timestamp: October 28, 2020, 06:04:01 am
content: Quote from: BrianHG on October 28, 2020, 12:06:35 amI have already planned out the display, it will be a lightbulb matrix connected to a character generator, connected to a video ram made of relays.

author: LondonNight
author_rank: Contributor
timestamp: October 28, 2020, 06:07:38 am
content: Quote from: BrianHG on October 28, 2020, 03:51:32 amI have already looked into latching relays, the best variant would be the 1 coil type. They are, unfortunately, very expensive, at around 0.60-1.00 usd per piece from china, for a lot of 1000 pieces. That is way too much than I'm willing to spend. Therefore, I will either keep using the capacitor ram, which was really cheap to make (80 usd tops) or, I will do the financial effort of building another ram from normal relays, those I can get for around 0.13-0.14 usd per piece, for a lot of 1000 pieces. Still expensive, considering how many I need, but not ridiculously expensive.

author: BrianHG
author_rank: Super Contributor
timestamp: October 28, 2020, 06:46:35 am
content: Quote from: LondonNight on October 28, 2020, 06:07:38 amWell understood. My goal was speed, not price. The nature of the 4poles & 2 polarities for the latched coil made an attractive 4 or 8 input and/or gate with optional invert on each input for logic if you used a + & - voltage supply driving the coils.Note if you are getting the 3D printer for the display, you can also create cam based CPU and ram like in the old pinball machines. They've manages quite a bit with 1 long shaft, a bunch of cams and a few external external relays for status, stop & go. Great for storing and running many fixed sequences.You can also make complex bit manipulation with these rotary processors like a 4x4bit adder with carry input and output including compare functions.Using 2x2 rotary sequencers, you could drive a full font display for a flip-dot display with X&Y cursor coordinates for a 16x16 character text mode, or a 128x128 pixel graphics display. The flip-dot hardware meets your guidelines as well as a rotary cam sequencer holding X&Y address coordinates and letter patterns. Not to mention raw flip-dot strings are dirt cheap and available today brand new. Though you will need to request not driving electronics, or a dummy back-plane with just wires to a connector. And since they store charge like cap memory, you may address them the same way.

author: BrianHG
author_rank: Super Contributor
timestamp: October 28, 2020, 07:12:45 am
content: I thought capacitors were against the rules....Because if resistors are allowed, cheap sub-1 cent reed switches with a single thick coil around them and a resistor on the other side can make a truly row/column memory addressable array where each bit can be set or cleared, with size of around 4mm2per bit. something like 32mmX1024mm per kilobyte. With additional row and column reed switches for for memory access in the 1ms range. Though, low-voltage high current & toasty resistors would need a good fan blower. Also, you would need to hand/wind all that magnet wire right on the reed glass to get that density. Less than a cent per bit. Also, you can make the equivilant of resistor/transistor logic gates, and/or/XOR/NAND like this which would run circles around those clunky huge relays since it is just 1 sing glass reed, and 2 or more magnet wire coils twisted in the same or opposite direction around the reed with a resistor or 2 strategically positioned at the right taps and the output would be latched. Now we are talking about a relay computer running 100 instructions a second on 2-3 volts, but something like 50-100 amps.You are no longer talking about an 8 bit adder running at 100hz, but maybe a full 16 bit adder & even multiplier running at 25Hz.(My mistake, you need 2 reeds per bit or logic gate combined flipflop for full speed. Only with ram you can get away with 1 reed per bit)

author: LondonNight
author_rank: Contributor
timestamp: October 28, 2020, 07:18:04 am
content: Quote from: BrianHG on October 28, 2020, 07:12:45 amCapacitors are not outside the rules. I will have a look at reed switches prices, altho it will take a while to wind magnet wire around 4000 reed switches...

author: BrianHG
author_rank: Super Contributor
timestamp: October 28, 2020, 07:38:25 am
content: Quote from: LondonNight on October 28, 2020, 07:18:04 amWith a 3d printer, even a cheap PLA plastic one, people have already made winding machines. It's just a spool and a worm-gear feeder to coil the wire neatly.Correction on the 2 reed switches, you only need 1, except, use the SPDT versions...Expect 1cent for a single NO device.Expect 10cents for a SPDT device.The trick to the logic gates and speed is 1 SPDT switch, but more than 1 drive coil in selected wind directions and wired in series or parallel. The reed is acting like a transistor. Once turned on, the third hold coil is held after the activation pulse by the resistor, where any incoming new logic on the next clock will override the hold resistor, or the resistor hold bus goes to a global reset for an 8 bit word or cpu register. Each coil is like another Gate input of the reed which would be a your mosfet.Now I'm talking about just the glass part you see below.The hold coil will need more turns as you want it to draw less current. The high speed gate coils underneath run strong for a pulse once every clock cycle.

author: Ian.M
author_rank: Super Contributor
timestamp: October 28, 2020, 07:56:33 am
content: For 4K of reed switches, it would be worth building an automated coil winding lathe. It should be possible to get the time to wind the coil(s) on one reed switch down to only a couple of minutes, including time to load/unload the lathe. Push soft plastic washers over the ends of the reed switch body to act as cheeks for the coil, one of them trapping the end of the magnet wire and spin it between 3D printed collet chucks, probably with small O rings to grip the body ends, driven by a gear motor with encoder, controlled by an Arduino. Use a RC servo to move the wire guide up and down the reed switch body to get even windings, controlling the servo and the gear motor from an Arduino or similar. You'll need some sort of wire tensioner - probably passing the wire between two felt disks backed by washers, with adjustable spring pressure would do.Unfortunately, I don't think one reed switch per bit addressable memory is practical. You could handle writing to it with row and column coils, both of which must be active to either pull it in, or cancel the holding coil's field to drop it out, but read addressing cant be handled that way. IMHO you'd need a second read switch per bit with row and column lines driving it, to couple the coil terminal of the selected memory reed switch onto the data bus.

author: Twoflower
author_rank: Frequent Contributor
timestamp: October 28, 2020, 08:03:00 am
content: Two things come to my mind using reed relais for this project.First, switching a coil or inductor with a reed relais will not work well if you dont have diodes (not allowed) to handle the self inductance if you switch off the current. The contacts will burn away very fast.Second, adding a piece of soft magnetic metal with high remance close to the reed relais could probably used as memory element. The writing coil needs eventually a little stronger to write the ‚memory‘. To delete the bit you need to feed a AC current through the coil. Not teste and i don‘t know if that would work out without extreme currents/coils. But again something you might be able to try for cheap.

author: LondonNight
author_rank: Contributor
timestamp: October 28, 2020, 08:34:48 am
content: Quote from: BrianHG on October 28, 2020, 07:38:25 amInteresting, I sat a lot with schematics in front of me, but never could make a memory with just 1 SPDT per bit. Would you mind showing me a schematic on how that is achieved? The best I could do is 2 SPSTs per bit.

author: BrianHG
author_rank: Super Contributor
timestamp: October 28, 2020, 08:39:48 am
content: Quote from: Twoflower on October 28, 2020, 08:03:00 amThe reeds are by-stable and the OP has experience with 2 polarity coils for set and reset. So, a weak low volt outer coil is always on which retains the memory bit whether set or reset. The inner coil either cancels or strengthens the outer one flipping the bit with a short pulse, akin to setting ferrite bead memory.Your idea is also valid as flipping the relay on takes more power for a short instant before the by-stable effect makes it easy to retain that bit. The ac signal may be a little bit of a problem.1 SPDT reed + 1 NC reed can make a perfect clean S-R relay without any resistor trick, but much more wiring. Ok for an ALU, but ugly expensive for ram.

author: LondonNight
author_rank: Contributor
timestamp: October 28, 2020, 08:52:11 am
content: Quote from: BrianHG on October 28, 2020, 08:39:48 amI believe you are mistaken, sir. Reed switches are monostable devices. That's why I don't understand how your logic goes. Rather than explaining with words, draw a small circuit which showcases the proof of concept. A simple circuit may be self-explanatory...

author: BrianHG
author_rank: Super Contributor
timestamp: October 28, 2020, 09:41:41 am
content: Move a magnet toward a reed relay, once close enough, it will turn on with a snap, however, pull away and you will notice the reed switch will stay on for awhile until it releases. The metal reed inside is designed like this so that there is a definite on and off state where a good contact hits. This happens because the 2 metal strips are touching and the magnetic field necessary to keep it closed once closed is a fraction of that required while the switch is open. Remember, applying a coil around a reed switch isn't the magnet, that coil is magnetizing the metal reed inside and it is attracting to it's other pole to close. Otherwise, the reed would stay stationary by charging the coil surrounding it and only an external magnet would actually work pulling the switch in a particular direction. Also, if that were the case, things are much worse as mounting a reed switch with the wrong rotation orientation means it would not work at all as the magnet would have pulled the switch apart instead of together and we know this is not how reed switches work.In fact, the differene is ABSURDLY huge, see here:See the 24v reed relay as an example, the data sheet says it takes 18v to switch on, but, once on, it will not turn off until the coil voltage drops below 2v. That is an insane clear cut by-stable range.Now, as an example, wire this relay like this:V24-----10k-----(A)---COIL-----GND(B)----SW------(GND) or row/column switches which will allow you to join (B) with (A) but you might get destructive reads.Wire (A) is your write port, pull (A) to V24 to set bit, pull (A) to GND to clear.Leave (A) alone, and the relay will retain it's last state since the coil will be at ~4v.(B) is your read port.With the glass reeds, you should be able to stack these vertically between 2PCBs like a sandwich with a row an column system on one side for write and the other for read. Or you can imagine other wiring configurations.(Bonus, the reed relay turns off in 0.5ms, now, that's fast. On is twice as fast...)Now what I was describing was the same idea, but with a thicker short coil so close on the glass with 1 or 2 winding layers thick only. Hence, low voltages, but high currents. This also means the switch on times will be faster than 0.1ms. You won't be able to do much about the turn off speed unless you reed source happens to be really short ones. Get 0.1ms turn off, and you can make a 1KHz machine if everything in theory was perfect, but only expect 100Hz and just focus on finding the best fastest SPDT reeds exclusively for the CPU and addressing row/columns for the memory addressing.

author: BrianHG
author_rank: Super Contributor
timestamp: October 28, 2020, 10:08:19 am
content: What about this:V24-----5k---((A)row)---COIL-----((A)column)-----5k-------GNDNow each bit latching bit has a row address and a column address....Short (A)row & (A)column together to clear a target bit in an XY array.Apply V24 to (A)row and GND to (A)column to set a target bit in the same XY array.I think, I need to sleep on this...Keeping the switches empty reserved for the reads means you can copy ram from 1 address to another write address really fast as a simultaneous operation.

author: richard.cs
author_rank: Super Contributor
timestamp: October 28, 2020, 10:08:31 am
content: Quote from: BrianHG on October 28, 2020, 09:41:41 amWell, the datasheet says it is guaranteed to turn on at 18V and to release at 2V, those specs could be met by it turning on and off at 12V. I agree that there is usually considerable hysteresis, butthatdatasheet does not specify how much. If I wanted to make use of the hysteretic behaviour I would start by finding a device that actually specifies it in the datasheet, this is fairly common, usually called something like "maximum release voltage" or "minimum holding voltage".

author: BrianHG
author_rank: Super Contributor
timestamp: October 28, 2020, 10:12:39 am
content: Quote from: richard.cs on October 28, 2020, 10:08:31 amThe min release of 2v is the key in this case. There is no way 4v will turn on this relay and it is 2x the min release. However, you are right. Some tests and verification needs to be done. Though, we wouldn't be buying relays, we are only buying the reeds since we also want some custom coils and we want tiny cheap.The SPDT units in the logic section have the added advantage we can enforce that turn on with 1k, no 10k as we have a switch contact reserved for it. The whole issue is price per bit and the SPST switch has the best price.For logic, 10cent for a SPDT through any other number of poles just by wrapping multiple glass reeds inside 1 coil gives us a switch contact to make a true hardened on-off mode, no worries about middle ground. But there are a fraction the number of reeds here.

author: akimpowerscr
author_rank: Regular Contributor
timestamp: October 28, 2020, 11:59:44 am
content: All this reasoning is very interesting, but it is based on a hypothesis which has not been verified and which is not certain at all:Is the magnetic field produced by a previously magnetized wire sufficient to cause the closing of reed contact's?There is obviously no question of breaking the glass bulb of the reed since it contains a protective gas in order to prevent the oxidation of the contacts.As long as this hypothesis is not verified experimentally, all other assumptions are in vain.So, the first thing to do is to check if it is practically possible to "read" the information of a magnetized metallic wire with the contacts of a reed relay.

author: LondonNight
author_rank: Contributor
timestamp: October 28, 2020, 02:04:05 pm
content: Quote from: akimpowerscr on October 28, 2020, 11:59:44 amI'm not interested in using magnetic wire, since it's not being produced anymore, hard to find, hard to use, and does not come in a caddy, like for example audio cassettes.

author: akimpowerscr
author_rank: Regular Contributor
timestamp: October 28, 2020, 02:30:33 pm
content: Quote from: LondonNight on October 26, 2020, 03:49:58 pm

author: LondonNight
author_rank: Contributor
timestamp: October 28, 2020, 02:42:21 pm
content: Quote from: akimpowerscr on October 28, 2020, 02:30:33 pmI reconsidered, after looking a bit more into that type of storage medium.

author: akimpowerscr
author_rank: Regular Contributor
timestamp: October 28, 2020, 03:01:40 pm
content: Ok, I'm just trying to figure out:You therefore discarded as storage medium:- the perforated paper tape- the magnetic wireYou keep only the magnetic tape as a storage medium, with information reading by magnetic head, like on an audio recorder;You are looking either for an electro-mechanical device sensitive enough to react to the signal coming out of the magnetic head, or a way to amplify this signal without using modern electronic components ...Is it correct ?

author: LondonNight
author_rank: Contributor
timestamp: October 28, 2020, 03:10:42 pm
content: Quote from: akimpowerscr on October 28, 2020, 03:01:40 pmThat is correct. As it was mentioned in the original post, I really want to use magnetic tape. I'm currently looking into amplidynes for amplifying the signal, but I'm open to suggestions.

author: LondonNight
author_rank: Contributor
timestamp: October 28, 2020, 03:17:50 pm
content: Quote from: BrianHG on October 28, 2020, 10:12:39 amIt is a bit off topic, but I'm gonna say it. I looked into the price of SPST reed switches from china, in bulk. The cheapest replies I got from the suppliers were at around 0.11-0.15 USD/piece for a lot of 4000 pieces. At that price, it is not worth it for me, I can just get normal SPDT relays for around that. This reed switch idea (just for the RAM, not for any combinational logic) got me really hyped up... but unfortunately, its not worth it.

author: akimpowerscr
author_rank: Regular Contributor
timestamp: October 28, 2020, 03:48:26 pm
content: As I said before, I have about ten pages of documentation on the operation of rotary amplifiers (amplidynes).Are you interested?I can scan them but I don't think I could post them here because it is in French, but I could send them to you as PM.These are pages 329 to 338 of the book "electrical control course" by Mr. TCHIUKIN, Soviet technique, MIR editions.As I also told you, amplidynes are rotating machines with brushes that are fragile and require a lot of maintenance.I have actually worked with amplidynes, I also know them in practice .... sincerely, your hope of amplifying signals of a few mV's with an amplidyne is totally in vain ....

author: LondonNight
author_rank: Contributor
timestamp: October 28, 2020, 04:40:03 pm
content: Quote from: akimpowerscr on October 28, 2020, 03:48:26 pmI appreciate you trying to help, but I really don't have anyone who knows french around here, to help me make sense of that documentation...

author: SilverSolder
author_rank: Super Contributor
timestamp: October 28, 2020, 05:17:35 pm
content: Quote from: LondonNight on October 28, 2020, 04:40:03 pmGoogle Translate?

author: BrianHG
author_rank: Super Contributor
timestamp: October 28, 2020, 05:21:29 pm
content: Quote from: LondonNight on October 28, 2020, 03:17:50 pmLOL, my first search on page 4:https://www.alibaba.com/product-detail/MKC17103-3foot-Magnetic-switch-reed-switch_62074966195.html?spm=a2700.galleryofferlist.normal_offer.d_title.cfe966e2s2J1RU&bypass=trueSPST might be less....With Alibaba, you also deal with these guys. Make a request that your requirements is 4k at 1 cent a piece and you are shopping around for cheaper SPST reeds as well. Never let them know how many you will be finally ordering, just ramp up the quantity as you need and you will get that 1cent each even down at 10k or below....I'm sure you can get your hands on 100 free samples so you may try a 8x8bit ram test & some logic.Note that my ram resistor example would be changes to 2 coils around 1 reed. 1 hold coil for every reed running at a low DC voltage, and a second coil in an X/Y array to apply a positive pulse to set the relay and a negative pulse to clear the relay. The switch will go to lamps above each bit so your memory array doubles as a dot-matrix display.However with SPDT or DPDT @ 1 cent per bit, you can make a solid on-off state per bit without relying on that pesky semi off-on low voltage/low current state.You should be able to construct a 8 bit binary counter for 24 cents worth of these 1 cent reeds while making 8 bit register latches for 9 cents. You are approaching 74LS logic IC prices.

author: cbutlera
author_rank: Regular Contributor
timestamp: October 28, 2020, 05:42:45 pm
content: I made the suggestion of an amplidyne without thinking too much about it, really just as an interesting example of an electromechanical device capable of amplifying a signal. Having thought a bit more about it now, the obstacles seem to be increasing. I rather suspect that akimpowerscr is right to be sceptical.The noise created by the commutator and any residual magnetisation obviously needs to be significantly smaller than the signal. I've no idea of the numbers on this.The gain of an amplidyne arises when most of the magnetic flux change seen by the armature comes from its rotation in the excitation flux. If the frequency of the signal being amplified is comparable to or greater than the rotational frequency, then most of the magnetic flux change seen by the armature will come directly from the changing excitation flux. In which case the whole thing looks more like a bad transformer.I don't know how fast a small home-made amplidyne could be made to rotate. A Dremel can get up to about 600 revolutions per second I think, so that's probably an optimistic upper limit. So the signal to be amplified needs to be no more than a few tens of hertz, or preferably less. Your suggestion of a 1kHz modulated tone is reasonably optimal for a tape head, but far to high to be directly amplified by an amplidyne. A much lower frequency recorded on the tape would provide a much lower signal power, so that's heading the wrong way. Some sort of demodulator is going to be necessary before the output of the tape head can be amplified by the amplidyne ... but with no semiconductors.

author: LondonNight
author_rank: Contributor
timestamp: October 28, 2020, 05:43:29 pm
content: Quote from: SilverSolder on October 28, 2020, 05:17:35 pmI was thinking about that, but then I realized he would send me scans of a phisical book, it's not like its a copy paste thing, I'd have to read from the scan, and put it in the google translate, imagine that

author: LondonNight
author_rank: Contributor
timestamp: October 28, 2020, 05:51:09 pm
content: Quote from: BrianHG on October 28, 2020, 05:21:29 pmAs I said, I messaged a few suppliers claiming they offer reed switches for a cent a piece, but they all gave me the "that price was incorrect" answer. I tell you what happens: They set the price to 1 cent per piece, so their posts come up first when someone searches for that product, but in real life, nobody in their right mind would sell reed switches for 1 cent or similar... They quoted the "correct" price for me for a bit over 10 cents.(Look at the attached image of this particular reply, Idk how to make the image appear big here)" alt="" class="bbc_img" />

author: BrianHG
author_rank: Super Contributor
timestamp: October 28, 2020, 05:52:36 pm
content: I need to know if you are going with magnetic wire recording or tape. The amplification is numerous orders of magnitude different between the 2. You can charge steel wire with bits which are strong enough to pull on a mechanical meter's needle, no fancy amplification. You are dreaming if you think you can do this with magnetic tape, even with my trick of using a 1/2inch wide video tape as a huge fat surface.This doesn't mean you cant try, however, to get 1/2inch wide tape to return a significantly strong enough signal, before worrying about your rotary amplifiers (amplidynes), make sure you can make a strong enough signal on the tape to begin with. You would need to think about a custom vertical head like I was describing a few pages back. You will also need to generate a strong enough ~single ms long record pulse to write data onto the tape when writing each bit.Reels of brand new unused magnetic wire are easy to come by, whether old or new. With new generic steel wire, you can go for a wire that is thick enough to hold a charged bits which will activate a home-made, long reed, or energize a coil playback read head which will only need 10-100x amplification by amplidyne to trigger a modern reed relay. With 1/2inch plastic tape, you will need 1000x to 10000x to achieve the same function, IE output playback electrical signal. Maybe 100x if you engineer your own specific playback head designed for the bit-size and frequency.As you can see, 38 gauge steel wire is plentiful and cheap:https://www.alibaba.com/product-detail/AWG-22-24-26-28-30_62272058701.html?spm=a2700.galleryofferlist.normal_offer.d_image.2c6216864TArXf&bypass=trueThe thicker the gauge, the less amplification you need for playback.Antique stuff:https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2380057.m570.l1313&_nkw=silvertone+record+wire&_sacat=0Note, if you truly want sturdy good modern record wire, look for old black-box flight recorders, they used steel wire to record flight data. This stuff wont tear and was designed to be recorded over again and again and again. Heat resistant too, tape would melt in a fire... They are also getting near megabit/second record resolution...

author: LondonNight
author_rank: Contributor
timestamp: October 28, 2020, 06:02:49 pm
content: People smarter than me here say that an amplidyne would be a pain to get working. I suppose, in the end, I will resort to using a vacuum tube or two to read magnetic tape. It's a sacrifice, but if it makes me avoid using paper tape and steel wire, then it's a sacrifice worth doing. Thank you all for pouring your knowledge here,I sure learned a few interesting things, such as the existence of the very interesting amplidyne.As it is, the topic is closed, but I'm not sure how to do that, since it's my first time posting. (I can't find the button to close the topic)

author: akimpowerscr
author_rank: Regular Contributor
timestamp: October 28, 2020, 06:15:52 pm
content: Amplidynes had a lot of applications during WWII and probably helped to win the war.It was good to remember their existence

author: BrianHG
author_rank: Super Contributor
timestamp: October 28, 2020, 06:44:50 pm
content: Quote from: LondonNight on October 28, 2020, 06:02:49 pmJust stop reading it. Or if you are subscribed, just un-subscribe.Others may add or ignore at their own whim...BTW, authentic 3.3cent reeds exist right from the manufacturer 'dy', 6 cent for SPDT.Unamplified reel-reel wire data recorder would have been a treat to see...

author: BrianHG
author_rank: Super Contributor
timestamp: October 28, 2020, 07:17:17 pm
content: A tiny amplidyne for your app would have been easy to make with an off the shelf quiet AC motor (Like those found in old turntables) tied to a BLDC motor which uses an electromagnet instead of one which uses permanent magnets, so long as you accept that your output signal would be an AC waveform. You would have gotten something like over 1000x gain with a device the size of 2 large chunky relays. IE, DC in from playback head tied to stator magnet, 1000x amplified power out, but changed into a 500hz AC sinewave.Off the shelf parts available today, but, topic closed...

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 28, 2020, 10:31:16 pm
content: Quote from: LondonNight on October 28, 2020, 06:02:49 pmNow the next challenge is to try to do it with the minimum number of tubes. I suspect it would be feasible to do it with just one, emulating the times when tubes were expensive and unreliable so minimizing their use would be important.