Obsolete technologies you never knew existed - Page 1
Forum section: electronics / general

author: tom66
author_rank: Super Contributor
timestamp: January 07, 2025, 01:51:38 pm
content: I recently discovered (after helping a friend repair their 20 year old portrait LCD monitor) the technology of piezo-electric transformers, as commonly used for CCFL backlights.There's a nice write up here...https://www.ti.com.cn/cn/lit/an/slyt107/slyt107.pdfI'm guessing, based on the publication date, and the rise of high performance white LEDs from about 2005 onwards, that such PZT CCFL drivers had a very short commercial lifespan. Probably under 10 years. Transformer-based CCFL inverters had been around for quite a while, I had an old satnav unit from a Mercedes that had a backlit CCFL LCD, dating back to the mid 90s (scrapped because it couldn't cope with the GPS week rollover), but such inverters tended to be too bulky for PDAs and other such devices. Mobile phones were already using white LED backlights from about 2005, with the first touchscreen phones launching around then.It seems PZTs are still around but the applications for them are quite limited. They can't handle very high currents so found a novel application for miniature CCFL backlights where a high voltage is needed at relatively low current (~3mA @ 700V).Any other obsolete technologies that people may be unaware of? Post them here.

author: squadchannel
author_rank: Frequent Contributor
timestamp: January 07, 2025, 02:01:04 pm
content: Nucolor technology in Tek TDS5xx,6xx,7xxhttps://hackaday.com/2019/01/17/sharpest-color-crt-display-is-monochrome-plus-a-trick/Also, CuriousMarc's videos are always interesting.

author: coppice
author_rank: Super Contributor
timestamp: January 07, 2025, 02:06:29 pm
content: I didn't know they did that for CCFLs, but I have seen a similar structure used to achieve several kilovolts in pulses at extremely low current.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: January 07, 2025, 02:07:20 pm
content: I don't think PZTs were ever common - simple transformers were cheaper - I've never seen one in any equipment, think I bought one from Digikey many years ago.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: January 07, 2025, 02:09:46 pm
content: My favorite obsolete tech is the Eidophor - hardly known as it was a niche product, absurdly complex and expensive, barely practical but owned its market for decades until DLPs and LCDs came along

author: coppice
author_rank: Super Contributor
timestamp: January 07, 2025, 02:10:19 pm
content: Quote from: mikeselectricstuff on January 07, 2025, 02:07:20 pmThey had severe space constraints for the CCFLs in notebooks, so they certainly wanted something very slimline like this technology. Whether it saw mass deployment I have no idea.

author: squadchannel
author_rank: Frequent Contributor
timestamp: January 07, 2025, 02:15:02 pm
content: and this

author: coppice
author_rank: Super Contributor
timestamp: January 07, 2025, 02:17:06 pm
content: Quote from: mikeselectricstuff on January 07, 2025, 02:09:46 pmThere are quite a few things like that. Technologies that are/were widely used, and millions of people have experienced the results, yet they have no idea these things existed. They might have had a "how the heck do they do that?" moment, and nothing more. The most amusing thing is when a young engineer tells you something you used to do routinely was impossible before the solution they learned in college was developed.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: January 07, 2025, 02:21:35 pm
content: https://en.wikipedia.org/wiki/IBM_1360https://en.wikipedia.org/wiki/SIGSALY

author: coppice
author_rank: Super Contributor
timestamp: January 07, 2025, 02:26:09 pm
content: Quote from: Alex Eisenhut on January 07, 2025, 02:21:35 pmQuoteAh, I miss the good old days when components were less fiddly than an 0102 resistor.

author: tom66
author_rank: Super Contributor
timestamp: January 07, 2025, 02:27:37 pm
content: Quote from: mikeselectricstuff on January 07, 2025, 02:07:20 pmApparently Apple used them in some of their laptops from around 2000 to 2005. After that they were replaced with LED backlights.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 07, 2025, 02:30:44 pm
content: The acoustic transformers were (and may still) used in laser printers / photocopiers to produce the high voltage. They may still be interesting for a few special uses, like when super high isolation and low coupling capacitance is wanted.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: January 07, 2025, 04:43:55 pm
content: Another good one is the Scanimate - it did geometric video effects, titles etc. using a monitor with a camera looking at it, and feeding the scan coil signals through an analogue computer

author: coppice
author_rank: Super Contributor
timestamp: January 07, 2025, 04:48:37 pm
content: Quote from: mikeselectricstuff on January 07, 2025, 04:43:55 pmThe Youtube page refers to scanimate.com, but it doesn't seem to be working. Shame.

author: coppercone2
author_rank: Super Contributor
timestamp: January 08, 2025, 02:14:49 am
content: the piezo transformer seems like it would pair well with the electrostatic motor that some people are talking about I think.i heard of them, I thought I even had one, but I gave up on it because I thought it would be hard to implement, but it turned out later that it was actually a regular transformer with a weird form factor (piezo transformers don't have windings!)

author: Halcyon
author_rank: Unknown
timestamp: January 08, 2025, 03:04:19 am
content: I don't have anything I can show, but years ago, the unit I worked in used IMSI Catchers manufactured by a very well known test equipment manufacturer (I'm 95% certain it was Rohde & Schwarz). The products weren't publicly advertised, and were only available to law enforcement and security agencies. Of course we had to comply with ACMA requirements and had all the relevant authorisations to operate the transmitters.The gear sat in a store room for quite some time before we did a clean-out about 5 years ago. It was really only good for downgrade attacks on 3G networks by that stage, but since 4G/LTE became available from about 2011, other methods of interception were used on modern networks.I'd have loved to have saved some of it from the industrial shredder, but the equipment was deemed classified. The existence of said equipment wasn't a secret, but nevertheless, it was kept quiet by the manufacturer and distributors.Similarly, when I worked for a fairly large telco, we had a "dark room" in our NOC, where only a handful of us were allowed access. To no surprise, it housed a bunch of equipment designed to intercept phone and internet traffic of customers at the time. Again, this was quite a while ago, things have largely changed.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: January 08, 2025, 04:56:06 pm
content: Quote from: coppice on January 07, 2025, 02:26:09 pmI like equipment rated in tons/bit.

author: eeproks
author_rank: Newbie
timestamp: January 08, 2025, 07:29:14 pm
content: QuoteAnother big telco vet here. Those rooms are still there, tho the tech has changed a bit. The google term you're looking for is "CALEA" aka "Lawful Intercept" (in the US...your governments telco big brother program will be called something else).

author: Halcyon
author_rank: Unknown
timestamp: January 08, 2025, 11:43:01 pm
content: Quote from: eeproks on January 08, 2025, 07:29:14 pmThanks for sharing. I haven't been inside a telco facility for a long time, but from my experience in law enforcement, the intercepts are just done remotely through various systems. Everything being digital these days, traffic can easily be routed or captured in all different ways. You don't really need anything "in series" with lines anymore.

author: coppercone2
author_rank: Super Contributor
timestamp: January 09, 2025, 12:32:28 am
content: and thats why the Chinese intelligence have a presence therehttps://www.lawfaremedia.org/article/calea-was-a-national-security-disaster-waiting-to-happenWhat is filled with 'obsolete' technologies is a old cell phone. Like those bricks. Its full of crazy RF parts. Usually big. I figure they are probably still in use for some military important things, maybe somewhat modernized.

author: wilfred
author_rank: Super Contributor
timestamp: January 09, 2025, 03:03:31 am
content: I saw a documentary on TV here in Australia about 10 years ago on the Olivetti Programma 101 programable calculator from the late 1960's. It used what they called a "magneto-strictive" memory which was a coil of wire through which pulses were sent. The string of pulses were the bits of the memory. Kind of analogous to mercury tubes used in earlier computers like CSIRAC in Australia.This wire was much more compact suitable for a desktop device. I found a copy of the doco on YT in Italian with some English translation. This is the point where the memory is shown.https://youtu.be/gm_XuJS7tZY?si=dBmax645VsXzYptE&t=1012

author: 5U4GB
author_rank: Super Contributor
timestamp: January 09, 2025, 04:52:55 am
content: Mag Amps. Some years ago I found an entire book on them in the engineering library here while looking up info on saturable reactors, a fascinating read. Their most barely-famous use was probably to implement the V2 guidance system.

author: coppercone2
author_rank: Super Contributor
timestamp: January 09, 2025, 05:00:21 am
content: I wonder what the high frequency limit of a mag amp is.You gotta wonder if you can saturate vacuum or something eventually to make a high frequency air core mag amp thing.https://en.wikipedia.org/wiki/Vacuum_polarizationthat seems to be a start

author: Kleinstein
author_rank: Super Contributor
timestamp: January 09, 2025, 09:18:03 am
content: Magnetic amplifiers are still used today. Many SMPS with multiple output voltages (e.g. PC supply) regulate the 2nd voltage via a saturable inductor (transductor). There is also another form of magntic amplifier, more a mechanical magnetic one. A generator with variable excitation is used to control the output voltage. This technique may look ancient and odd to some EEs, but is still used today in many alternators.For a mag amp one has to distingush between the excitation frequency and the usalble output / control frequency. The excitation has to be well higher.There is no saturation in vaccum and also in diamagnets the saturation is too weak and too high a field to be usable. So one is limited to ferromagnetic materials like ferrites.A magnetic oddity that is no longer used is magnet based logic. A bit similar to core memory, but for logic functions. It was uses in the Apollo computers (Nice videos from Curious Marc about these).

author: tggzzz
author_rank: Super Contributor
timestamp: January 09, 2025, 10:00:15 am
content: Quote from: Kleinstein on January 09, 2025, 09:18:03 amFor examplehttp://theadamsons.co.uk/elliott803.htmSee an Elliott 803B operating at TNMoC. You can also see the world's oldest working computer operating (literally, since it is based on dekatrons), working reconstructions of famous WW2 "computers, and working big iron.Well worth a visit, andifyou have time left over it might be worth visiting Bletchley Park next door.

author: SteveThackery
author_rank: Super Contributor
timestamp: January 09, 2025, 11:30:06 am
content: Magnetic amplifiers were also used in the UK telephone network back in the days of Strowger switching.There was a device called the LLIR (local line insulation routiner) - also called the "liar" as its findings were unreliable. Every night it would step its way through the phone lines, testing for low insulation between the wires, low insulation to earth and low insulation to -50V, using the magnetic amplifier to perform these tests. It was extremely finicky and required weekly setting-up, indicating that the design had room for improvement.Each line test made the customer's telephone bell give a single "ding". A problem arose because the LLIR was set up to work with a four-digit numbering scheme. When it was testing a remote satellite exchange with only three-digit numbering, each customer's bell dinged ten times, driving them nuts. I modified the LLIR at Matlock exchange (Derbyshire, UK) not to do that.The LLIR was less useful for identifying individual line faults because it was more sensitive than the test equipment available to the linesmen, so many "faults" were given up on and closed as "Fault Not Found" (FNF). However, where it shone was in finding clusters of faults all on the same cable, giving an excellent early warning that the cable was on its way down - typically due to water ingress. Occasionally a connector block at the top of a pole would be left open and the LLIR would sometimes pick that up if rain got in the block.

author: Aninjaflamingo81
author_rank: Newbie
timestamp: January 09, 2025, 03:43:46 pm
content: Not electronics related, but still interesting. From approximately 1974 to 1976, honda had released 2 motorcycles with torsion valve springs borrowed from their racing engines. From my ignorant understanding it was an early attempt to mitigate valve float at high rpm.https://en.m.wikipedia.org/wiki/Honda_CB450

author: tom66
author_rank: Super Contributor
timestamp: January 09, 2025, 04:19:06 pm
content: Magamps used to be commonly used to provide the 3.3V rail in an ATX computer power supply (12V and 5V usually via the main transformer), though the solution nowadays is a pair of high current buck converters that provide that supply from the 12V rail. It is difficult to make an ATX supply meet the more stringent cross-rail loading requirements of the newest Intel specification otherwise (where 12V has very low load as CPU goes into sleep, but 5V/3.3V still decently loaded.)

author: themadhippy
author_rank: Super Contributor
timestamp: January 09, 2025, 04:22:51 pm
content: QuoteThey also played with oval pistons and 8 valves per cylinder

author: coppice
author_rank: Super Contributor
timestamp: January 09, 2025, 04:55:33 pm
content: Quote from: themadhippy on January 09, 2025, 04:22:51 pmI'd love to see how those oval cylinder bike engines were made. Making a precision oval seems like it would be rather expensive.

author: themadhippy
author_rank: Super Contributor
timestamp: January 09, 2025, 06:19:15 pm
content: Quotejust had a quick google, i remember them being expensive but £38k in 1992,my 535cc yammy i bought in 91 was less than £3k on the road

author: Analog Kid
author_rank: Super Contributor
timestamp: January 09, 2025, 09:51:47 pm
content: How 'bout the rotary (Wankel) engine used by Mazda? I thought those were pretty kewl when I was a kid back in the 19-ought-60s.

author: coppice
author_rank: Super Contributor
timestamp: January 09, 2025, 09:58:25 pm
content: Quote from: Analog Kid on January 09, 2025, 09:51:47 pmI think most people know that existed.

author: TimFox
author_rank: Super Contributor
timestamp: January 09, 2025, 10:12:08 pm
content: Quote from: coppice on January 09, 2025, 09:58:25 pmFewer people remember various attempts at using rotary valves instead of poppet valves in internal-combustion engines.Seehttp://www.douglas-self.com/MUSEUM/POWER/unusualICeng/RotaryValveIC/RotaryValveIC.htm

author: themadhippy
author_rank: Super Contributor
timestamp: January 09, 2025, 10:31:06 pm
content: Quotemazda pah,nortons are were the real wankel fun lives.

author: coppice
author_rank: Super Contributor
timestamp: January 09, 2025, 10:34:42 pm
content: Quote from: themadhippy on January 09, 2025, 10:31:06 pmNah, the NSU RO-80 was the Wankel king. They had a terrible reputation for wearing out fast. However, some people used them for courier service, where they spent most of their time at high speed on motorways. Used like that they were very reliable, and ran for ages.

author: themadhippy
author_rank: Super Contributor
timestamp: January 09, 2025, 10:51:28 pm
content: As we've wander into engine territory an honorableorrible mention must go to royal enfield for the taurus, who ever though chucking a diesel engine into a motorbike was a good idea.

author: tom66
author_rank: Super Contributor
timestamp: January 10, 2025, 12:16:48 am
content: I read somewhere of a Soviet motorcycle that had a novel feature where the bike lacked a reverse gear (as most bikes do) but the engine could be started and operated in reverse for short durations. Should be possible with a two-stroke engine if I understand correctly, you'd just need to run the starter backwards. I'm not sure if it was a party trick and I can't find any reference to it on the internet anymore so it may have been a legend. Anyone know what it might have been?

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: January 10, 2025, 12:47:49 am
content: https://en.wikipedia.org/wiki/Backward-wave_oscillator

author: Canis Dirus Leidy
author_rank: Regular Contributor
timestamp: January 10, 2025, 01:41:13 am
content: Quote from: coppercone2 on January 09, 2025, 05:00:21 amIn the books from the"Библиотека по автоматике" series, it was mentioned that frequencies in the hundreds of kilohertz were reached (in sixties). However, the mass-produced magnetic logic elements worked, for obvious reasons, at frequencies of 50 and 400 hz.On a related topic.A some of Soviet ferroresonance AC-voltage stabilizersfor household use.

author: jonovid
author_rank: Super Contributor
timestamp: January 10, 2025, 02:44:36 am
content: some time in the 1980s SONY made CRT's for portable use.compact 4 inch flat screen 1 inch deep SONY CRT's for a portable TV type watchmanwith front of screen projection that you look inside the 1 inch deep CRT tube at the monochrome phosphorescent screen.the 4 inch CRT was the shape of a hip flask bottle with the screen window on one side.still available today as new old stockhttps://www.aliexpress.com/item/1005001659366793.html?spm=a2g0o.productlist.main.5.23eai3A4i3A4a5&algo_pvid=764e334c-4c84-4a81-9f6a-ff009775f5f1&algo_exp_id=764e334c-4c84-4a81-9f6a-ff009775f5f1-2&pdp_npi=4%40dis%21AUD%2138.49%2129.00%21%21%2123.52%2117.72%21%40210318e817364750173234278e23e1%2112000040396030525%21sea%21AU%210%21ABX&curPageLogUid=jLTMJNTExdf3&utparam-url=s

author: Analog Kid
author_rank: Super Contributor
timestamp: January 10, 2025, 03:26:14 am
content: That's interesting.Trying to figure out how that works: the axis of the CRT is perpendicular to the screen.Is there a mirror?Or it looks like the phosphor surface is slightly curved perpendicular-ish to the beam.Looks like it works pretty well. Very clever.

author: Swainster
author_rank: Frequent Contributor
timestamp: January 10, 2025, 03:43:19 am
content: Those mini projection CRTs were very commonly used in Japan for video doorbell phone in apartment blocks.

author: cunningfellow
author_rank: Regular Contributor
timestamp: January 10, 2025, 04:24:03 am
content: google Clive Sinclair folded CRT and you should get some asnwers

author: 5U4GB
author_rank: Super Contributor
timestamp: January 10, 2025, 05:18:49 am
content: Quote from: TimFox on January 09, 2025, 10:12:08 pmAlso, the rotary engine gets reinvented every few years as some breakthrough new technology that then dies a slow death as the funding burst from the initial blaze of publicity dries up.

author: Analog Kid
author_rank: Super Contributor
timestamp: January 10, 2025, 06:39:37 am
content: Quote from: cunningfellow on January 10, 2025, 04:24:03 amI did that and found a few links, but what I didn't find was any diagram or picture showing how those tubes worked.I'm still curious to know that.

author: tooki
author_rank: Super Contributor
timestamp: January 10, 2025, 08:50:34 am
content: Quote from: Analog Kid on January 10, 2025, 06:39:37 amI can only assume you’ve never seen one in person? It’s super obvious when you see them in operation: the phosphor isn’t on the face of the CRT, but on a flat (well, actually slightly curved) target within, and it’s at roughly 45 degrees. Watch some videos about them, it’ll be really clear.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: January 10, 2025, 10:53:21 am
content: Even better, search for Aiken thin CRT.https://www.semanticscholar.org/paper/History-of-the-Kaiser%26%238212%3BAiken%2C-thin-cathode-ray-Aiken/b1962b9a0a066a16ccc5d1b76b8c6464da121ca2Or other approaches to color CRTshttps://www.earlytelevision.org/geer_color_crt.htmlA type of vacuum tube, I think this is the "thermionic integrated micro module"http://www.hts-homepage.de/Silizium/Silizium.htmlA vacuum tube ADChttp://electricstuff.co.uk/glassadc.html(keep scrolling that one for the tube memory)

author: coppice
author_rank: Super Contributor
timestamp: January 10, 2025, 11:02:55 am
content: Quote from: Alex Eisenhut on January 10, 2025, 10:53:21 amThat was developed for digitising the telephone network, but I think they had shifted to a semiconductor approach by the time the first T1 systems were put into service in the PSTN in 1962. You'll notice the sampling rate was 8ksps, just like the final PCM telephone system.

author: temperance
author_rank: Super Contributor
timestamp: January 10, 2025, 03:35:59 pm
content: In some countries they had wired radio:Sublime technology.

author: Bobson
author_rank: Regular Contributor
timestamp: January 10, 2025, 04:06:31 pm
content: Not had, but have.

author: schmitt trigger
author_rank: Super Contributor
timestamp: January 10, 2025, 04:14:14 pm
content: Unless one has seen the inside of a 1950s-era automobile radio, the vibrator power supply comes to mind.

author: coppice
author_rank: Super Contributor
timestamp: January 10, 2025, 04:43:52 pm
content: TVs and radios used to be expensive. In the UK, Rediffusionhttps://en.wikipedia.org/wiki/Rediffusionset up shops in neighbourhoods where they received all the broadcast TV and radio channels, and used racks of amps in the shop, to drive long twisted pairs that went to the surrounding houses. They supplied simplified radios and TVs to their subscribers, which lacked any receiver section. Channel selection was a matter of selecting the right twisted pair with a switch on the radio or TV. I used to walk past one of these shops on the way to school in the 1960s. They had some big racks of electronics, with the largest vacuum tubes I have seen in a consumer application. The cost and power consumption of the equipment in the shop must have been considerable. Apparently that, and all the cabling costs, was still cheaper than having tuners in each set.

author: schmitt trigger
author_rank: Super Contributor
timestamp: January 10, 2025, 06:04:57 pm
content: In the winter, these huge tubes would nicely complement wood stoves to provide warmth.The glow emanating from the tubes would add to the cozy factor, much like a fireplace.Warmth and a soft glow, plus music. Beautiful!

author: Analog Kid
author_rank: Super Contributor
timestamp: January 10, 2025, 08:22:54 pm
content: Quote from: schmitt trigger on January 10, 2025, 04:14:14 pmI knew about those. Those "choppers". Pretty appropriate solution for the time before solid-state electronics.

author: Analog Kid
author_rank: Super Contributor
timestamp: January 10, 2025, 09:09:02 pm
content: Quote from: tooki on January 10, 2025, 08:50:34 amDave's video on thisis excellent.When I saw some pictures of another implementation of this (a Sony), it looked to me as if they were directing the electron beam at an angled phosphor target, like the first sketch here:Which, as Dave points out, would result in a pretty unfocused image.However, I didn't know about the "repeller" part of this scheme (bottom sketch). Very tricky how they make those electrons turn on a 90° flight path into the front-facing phosphor screen.Very clever arrangement.

author: Canis Dirus Leidy
author_rank: Regular Contributor
timestamp: January 11, 2025, 03:42:13 am
content: Optical sound recording on paper tape (Description in English by Douglas Self) from the Thirties:P.S.The penultimate image on the link is actually the Eighties — then there was a reissue on a vinyl record.

author: TimFox
author_rank: Super Contributor
timestamp: January 11, 2025, 04:33:29 am
content: The Douglas Self website has a huge collection of archaic and obsolete technologies, along with unusual musical instruments and other hardware.

author: Andy Chee
author_rank: Super Contributor
timestamp: January 11, 2025, 05:26:12 am
content: Quote from: Analog Kid on January 10, 2025, 03:26:14 amAdrian did a bit of experimenting with that exact aliexpress low-profile flat CRT.I also have one in my junkbox in doorbell form.

author: BrianHG
author_rank: Super Contributor
timestamp: January 11, 2025, 05:35:41 am
content: Holy Sh-t, a portable broadcast VCR from 1967...https://www.eevblog.com/forum/chat/holy-sh-t-a-portable-broadcast-vcr-from-1967/msg5777521/#msg5777521

author: RoGeorge
author_rank: Super Contributor
timestamp: January 11, 2025, 07:40:55 am
content: Quote from: Andy Chee on January 11, 2025, 05:26:12 am$22?!I want one.Not obsolete tech, still in use, but very unexpected when I've first found out: The wax actuator. Usually a piston filled with wax, and a resistor heats the wax. When heated/cooled the wax changes its volume and moves the piston. Pretty slow, but very strong, small and silent.https://en.wikipedia.org/wiki/Wax_motorhttps://www.aerospacemanifolds.com/thermal_actuators.html

author: Haenk
author_rank: Super Contributor
timestamp: January 11, 2025, 08:25:22 am
content: Quote from: wilfred on January 09, 2025, 03:03:31 amThis was the "common" type of memory used in all desktop calculators that required more than a few bits of storage, before core memories became large enough.However they had a serious problem (by todays standards) - they were serial FIFO memories, no "RANDOM ACCESS" whatsoever.I really suggest to read about the DIEHL COMBITRON; Wolfgang Robel made a video about it, too. That machine added another level of craziness on top. (And I have one, stored away...)

author: RoGeorge
author_rank: Super Contributor
timestamp: January 11, 2025, 10:05:33 am
content: Another funny one, the Optical Pen. It was turning an unmodified TV screen into some sort of a "touch screen". A pencil with a photodiode at its tip was pointing at the TV tube, while the image was flashing, half black half white, so to find out in which half of the screen the pencil is pointing. And so on, flashing and halving the X and Y axis at each step, until the pen was fully located on the screen. I guess epilepsy was not yet a thing back in the 80s.The calibration and demo start at minute 2, first part is loading the software from a cassette tape.Dk' Tronics Lightpen for ZX Spectrum (1983) - testFrancesco ScagnelliAnother way to implement a "touch screen" for a display was to put a frame around the screen, and in the frame there were embedded IR LEDs on the X and Y axis, and they were pointing to some IR photodiodes located on the other side of the frame, in opposition with the IR LEDs. The idea was that touching the screen with the finger will block the IR light coming from the IR LEDs on the X and Y, thus locating the position of the finger relative to the screen.

author: tom66
author_rank: Super Contributor
timestamp: January 11, 2025, 10:50:26 am
content: I wonder if that's similar to how the LG PenTouch plasma TVs worked. They only released this product for plasma TVs - if you embedded a hidden subfield with binary coding data into it, you could probably detect that with a synchronised photodiode. Most plasma TVs flashed the image 600 times per second, with 10 subfields per real display frame, each subfield having differing on-times to create 10 bits of intensity control. I haven't found any detailed info on how they did this, but they never released it for LCD TVs, which suggests it's not a capacitance or resistance sensing mechanism but something related to the plasma panel itself.https://www.trustedreviews.com/reviews/lg-pentouch-tv-first-look

author: tggzzz
author_rank: Super Contributor
timestamp: January 11, 2025, 12:43:48 pm
content: Quote from: TimFox on January 11, 2025, 04:33:29 amhttp://www.douglas-self.com/MUSEUM/museum.htmLooks like that trumps this thread!

author: tggzzz
author_rank: Super Contributor
timestamp: January 11, 2025, 12:58:45 pm
content: Pneumatic logic; and, or, not, SR flip-flops, regenerator, sequencers.https://www.parker.com/literature/Literature%20Files/pneumatic/UPD_100108/PCC-Logic.pdfI once did a feasibility study where I recommended against replacing hydraulic logic with a microprocessor. Electricity and gas-air mixtures don't mix.

author: coppice
author_rank: Super Contributor
timestamp: January 11, 2025, 02:34:56 pm
content: Quote from: RoGeorge on January 11, 2025, 10:05:33 amI never saw that, but light pens to pick things from a raster scanned screen were commonplace. They usually checked the horizontal and vertical position of the scan at the moment a bright pulse was detected by the pen. Even the darkest part of the image glowed enough for the pen to detect a small pulse.Quote from: RoGeorge on January 11, 2025, 10:05:33 amThat technique is still used today. It has been shrunk to a very slim plastic light pipe moulding around the edge of the display. Its commonplace with e-paper screen devices, like the Kindle. Some cars have used it (I think my Volvo works that way). Its also used for some medical applications, and other places, where people need to touch screens with gloves and very messy hands.

author: tggzzz
author_rank: Super Contributor
timestamp: January 11, 2025, 03:58:33 pm
content: Quote from: coppice on January 11, 2025, 02:34:56 pmI think I still have one somewhere.In the late 70s I thought it would be a nifty way of selecting something on the screen - long before mice were known outside Xerox PARC, of course. Never got around to it, of course.They were definitely used in 60s military equipment with vector displays. That made it trivial to correlate the photodiode's blip with the relevant object.They also indicated why you should never use large touchscreens for long: while mice bugger your wrists, lightpens (and similar) bugger your shoulders. (And trackballs bugger your thumbs).

author: coppice
author_rank: Super Contributor
timestamp: January 11, 2025, 04:13:17 pm
content: Quote from: tggzzz on January 11, 2025, 03:58:33 pmI question whether they were actually used in deployed military equipment, for the reason you stated. In the mid 70s we started developing a military system with a light pen, but the fatigue it caused meant we had to change that out for a trackball. A light pen can work well for occasional selection of points on a screen, but most military applications require endless selection for hours at a time. The little trackballs that went into a lot of early notebooks can make your thumb ache, but a large one sunk into the worktop, which you can spin with your palm can work pretty well. I suspect the light pens you see in movies and documentaries about the military are prototype systems.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 11, 2025, 05:11:39 pm
content: The optical pen type was even implemented with some home computers. I build one for the C64, using a metal can transistor with hole drilled in the top. That was all the electronics needed. Many ready made phototransistors where at bit on the slow side, but some also worked.

author: iMo
author_rank: Super Contributor
timestamp: January 11, 2025, 05:32:54 pm
content: I had that (DIY) light pen for ZX Spectrum.. Rather a joke, but basically it worked.Another technology from that time was transmitting the ZX Spectrum programs via commercial FM broadcast, or bundling programs into some computer magazines on "flexible vynil records". I tried both and it worked too..

author: themadhippy
author_rank: Super Contributor
timestamp: January 11, 2025, 05:44:31 pm
content: Quotein the uk they used the tv via teletex ,but only for the bbc computers

author: CatalinaWOW
author_rank: Super Contributor
timestamp: January 11, 2025, 07:57:21 pm
content: While the half interval method for finding the location of a light pen conceptually works, it is hard to believe that they actually used that. Far simpler to just measure the timing of the pulse from the pen relative to the horizontal and vertical sync signals. Easy to get if the pen is integrated with the display, and not that hard to synthesize even without wired connection to the monitor. This allows position update once per frame (or twice per frame on interlaced signals if you are willing to accept 1 line of vertical error). And no epilepsy triggers worse than standard TV. The half interval method would require several frames to get lower positional accuracy.

author: RoGeorge
author_rank: Super Contributor
timestamp: January 11, 2025, 09:51:09 pm
content: In theory, yes, but in practice it was not that easy.The inertia of phosphorus tubes is high, tens of ms, and depends from one TV to another. Those who were selling the home computers were usually selling them without a monitor, and the buyer was using whatever TV was heaving at home.Then, the CPU back then was clocked at only a couple of MHz, for example the ZX Spectrum from the video was with a Z80, an 8 bit microprocessor, and clocked at only 3.5MHz. Same processor was handling the read/writes to the video RAM, plus the execution of whatever code was running.The total screen was 384 pixels wide, out of which 256 pixels were the useful video image, and the rest were border. A typical TV line has 64us, out of which about 12us or so (don't recall exactly) were sync pulses. The fastest CPU instruction was taking 4 clocks at 3.5MHz. During this CPU instruction, the electrons spot was traveling along 8 image pixels. Not to say, most instructions were 2-4 times longer than the minimum possible 8 pixels.The timing was very tight, and everything was heavily optimized. Not much room was left to detect a pencil position. There were no dedicated hardware counter/timers yet, like there are in the nowadays microcontrollers, so all timings were to be done in software. If exact timing was needed, you were writing each machine code mnemonic in your loop on a piece of paper, and count the total numbers of clocks needed to execute one loop.Or else, add dedicated hardware (for example a Z80 CTC, which was another chip on the same data and address busses, very similar with the nowadays PWM/counters from MCUs). But adding hardware extensions was expensive.

author: Njk
author_rank: Frequent Contributor
timestamp: January 11, 2025, 10:32:12 pm
content: Quote from: schmitt trigger on January 10, 2025, 04:14:14 pmSeen that in my father's car. A devices like that were sometimes called umformers. Produced a hum sound, similar to a cooling fan. BTW the old loudspeakers also produced some hum because there were no permanent magnets. Instead, the magnetic field was created by passing a (usually poorly smoothed) DC through a dedicated winding in the base part. The hum was quite annoying.

author: TimFox
author_rank: Super Contributor
timestamp: January 11, 2025, 10:42:16 pm
content: The electromagnet coil in those loudspeakers normally was used as part of the rectifier filter circuit (filter choke) when useful permanent magnets were expensive or unavailable.

author: Gyro
author_rank: Super Contributor
timestamp: January 11, 2025, 10:59:08 pm
content: The Scophony TV probably deserves a place in here. A pre-war large screen (24" x 22" domestic, much larger for theater) projection TV that got displaced by the advent of smaller, cheaper, radar CRT production during WWII.The TV used a 300W Mercury arc lamp, mechanical scanning of line and frame frequency mirrors using valve amplifier driven motors (the line scan motor running at 30k+ rpm), capable of 405/441 line display. It also passed the light through a supersonic crystal driven liquid column delay line cell (Jeffree cell), synchronized to the line scan mirror which allowed a huge increase in light output compared to single spot scanning.I remember a more in-depth article in an old issue of Wireless World but tracking it down is proving difficult.https://www.earlytelevision.org/yanczer_scophony.html

author: tggzzz
author_rank: Super Contributor
timestamp: January 11, 2025, 11:34:02 pm
content: Quote from: RoGeorge on January 11, 2025, 09:51:09 pmThe software speed you mention is irrelevant, since it has to be done in hardware.With a little imagination you don't need a dedicated timer chip.Data was stored in RAM, with that RAM's address changing every character (or bit) in synchrony with the screen position. Connect that RAM's address line to a dedicated hardware register's inputs. When the photodiode blips, clock the register thus storing the address related to the character (or bit) at that time. Read the register at your leisure, and use the relevant algorithms to convert it to the X-Y coordinate and/or relevant "object".

author: tooki
author_rank: Super Contributor
timestamp: January 12, 2025, 12:13:42 am
content: Quote from: temperance on January 10, 2025, 03:35:59 pmIf I’m reading the comments correctly between the lines, it’s not radio at all, but just a public 100V PA system, and the little “receiver” is simply a small PA speaker?

author: Njk
author_rank: Frequent Contributor
timestamp: January 12, 2025, 02:57:07 am
content: Quote from: tooki on January 12, 2025, 12:13:42 amIn fact, it was a cable radio system designed to make the user's terminal devices very cheap. Basically, the terminal can be just a loudspeaker and a small step-down transformer, since the line voltage was about 30 VAC to compensate for long length of the cable network. Later, the system was enhanced by adding two HF sub-carriers for two more programs. That required more complex terminals with the de-multiplexing capability

author: tooki
author_rank: Super Contributor
timestamp: January 12, 2025, 10:39:54 am
content: Quote from: Njk on January 12, 2025, 02:57:07 amSo… a PA system, just like I said? No actual radio (RF) involved.Quote from: Njk on January 12, 2025, 02:57:07 amGotcha.

author: RoGeorge
author_rank: Super Contributor
timestamp: January 12, 2025, 11:56:45 am
content: Quote from: Gyro on January 11, 2025, 10:59:08 pmThat reminds me of another now obsolete device, the ark mercury rectifier. They were used a lot in the past.Picture fromhttps://en.wikipedia.org/wiki/Mercury-arc_valveSome were about as big as a washing machine, full of high voltage and glowing!!!Another device in use for a while, electromechanical radio transmitters based on Alexanderson alternator.One is still functional, transmitting once a year for the delight of VLF hams.QuoteQuote fromhttp://www.jproc.ca/radiostor/aalt.html

author: Bobson
author_rank: Regular Contributor
timestamp: January 12, 2025, 12:00:39 pm
content: Quote from: Njk on January 11, 2025, 10:32:12 pmNope. Umformers are motor-generators, having a motor and generator on one axis frequently with an aid of flywheel. I'm sure the correct English term is motor-generator, umformer is of German origin.

author: Njk
author_rank: Frequent Contributor
timestamp: January 12, 2025, 12:04:56 pm
content: Quote from: tooki on January 12, 2025, 10:39:54 amYes and it's still in use with exactly PA purpose as it does not require power. It's available in every household by default and the user have to pay a monthly subscription fee. User wishing to get rid of it have to perform the procedure with service cancellation fee.

author: Njk
author_rank: Frequent Contributor
timestamp: January 12, 2025, 12:10:22 pm
content: Quote from: Bobson on January 12, 2025, 12:00:39 pmGermany is closer to Russia than England so German terms are historically in wide use. Generally, umformer means converter

author: PA0PBZ
author_rank: Super Contributor
timestamp: January 12, 2025, 12:36:32 pm
content: Quote from: Bobson on January 12, 2025, 12:00:39 pmI think that when both are on the same axis it's called dynamotor, not? And of course Dutch is close to German as usual, "omvormer".

author: valcher
author_rank: Contributor
timestamp: January 12, 2025, 01:02:20 pm
content: I remember in the 60s of the last century in Christmas tree garlands they used incandescent lamps with a bimetallic plate to create a blinking effect. When current flowed through the lamp spiral, the plate heated up and opened the garland circuit, as it cooled down, the circuit closed and everything repeated again.

author: RoGeorge
author_rank: Super Contributor
timestamp: January 12, 2025, 02:00:02 pm
content: You mean like this (closeup photo at minute 00:25)?Still have on of those incandescent light bulb with bimetallic switch.Same idea of a bimetallic switch was used in the battery charger regulator in the first models of Dacia 1300 (a Romanian manufactured car). Inside an isolated box there was a spiral of heating wire, and a bimetallic switch in series, to control the intensity of the excitation field of the car's alternator, thus regulating its output voltage. In practice, that regulator was never working properly. Everything was influencing its regulation, from temperature, to altitude, to humidity, to motor speed, to road type (because of vibrations), and so on.

author: squadchannel
author_rank: Frequent Contributor
timestamp: January 12, 2025, 02:04:58 pm
content: Christmas tree bulbs, until a ten years ago.When they went out, the whole bunch would go dark, so I had my dad change them. can't even get the bulbs, so now they're LEDs.

author: Gyro
author_rank: Super Contributor
timestamp: January 12, 2025, 02:44:28 pm
content: Quote from: RoGeorge on January 12, 2025, 02:00:02 pmI remember buying one of those as a kid. My dad wasn't happy when he had to start replacing other (fine but ageing) bulbs in the string!Wiring a florescent lamp starter in series would produce a much more random flashing effect.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: January 12, 2025, 03:53:00 pm
content: Bimetal switches are a great example of a technology once widely used and dying now now. Thermostats, blinkers for car turn signals and warm up timers are prior applications that are gone. They still hang on in circuit breakers and thermal safety switches.

author: TimFox
author_rank: Super Contributor
timestamp: January 12, 2025, 04:15:26 pm
content: An interesting technology analogous to bimetal strips is a piezoelectric "bimorph".https://piezodirect.com/piezoelectric-bimorph/A simple piezo actuator can exert a large force, but only for a very short expansion.When a larger motion is required, the bimorph (described in that citation) allows a much larger "wiggle" at much lower force.

author: coppice
author_rank: Super Contributor
timestamp: January 12, 2025, 04:20:33 pm
content: Quote from: CatalinaWOW on January 12, 2025, 03:53:00 pmBimetal switches have been displaced from many applications, but I don't think they are going away any time soon. In many applications where it formed a controllable thermostat its being displaced by true temperature measurement devices, offering greater control. However, for things like a kettle cutout, when steam flows over a bimetal device, it needs little precision or controllability, and i think its likely to stick around for quite a while.

author: valcher
author_rank: Contributor
timestamp: January 12, 2025, 04:57:45 pm
content: Quote from: RoGeorge on January 12, 2025, 02:00:02 pmYes, this is exactly the type of light bulbQuote from: Gyro on January 12, 2025, 02:44:28 pmConnecting the starter to the circuit caused unpredictable flashing of the lamps.Thermal switches are still used in automatic switches, in protective relays for overloading electric motors, in thermostats for maintaining the temperature of industrial equipment control cabinets. It is too early to write off bimetal switches, they are cheap and reliable.

author: SteveThackery
author_rank: Super Contributor
timestamp: January 12, 2025, 05:35:10 pm
content: Quote from: coppice on January 12, 2025, 04:20:33 pmHey,@coppice, I'm not sure, but I seem to think most kettles use a "muscle wire" steam detector these days.

author: Gyro
author_rank: Super Contributor
timestamp: January 12, 2025, 06:38:17 pm
content: No, bimetal is still pretty much universal. It can be formed into pre-stressed disc shapes where they exhibit a snap action of considerable force, rather than the slow action of muscle wire. Much easier to implement fast break contact actuators.Edit: A typical example...https://www.eevblog.com/forum/repair/repairing-an-electric-kettle/msg5774927/#msg5774927

author: Njk
author_rank: Frequent Contributor
timestamp: January 12, 2025, 06:54:26 pm
content: Quote from: SteveThackery on January 12, 2025, 05:35:10 pmThis is my electric kettle. It has a quite complex mechanics inside the cap that requires periodic cleaning otherwise the steam detector switch does not work reliably because of high steam leakage. Also, it has a bi-metallic thermal switch that is proved very useful as it many times saved the kettle from overheating when all the water evaporated. About a year ago I'd modified it specifically to make the maintenance easy. Seems the time to do the maintenance again. Thanks for the reminder.

author: coppice
author_rank: Super Contributor
timestamp: January 12, 2025, 07:07:24 pm
content: Quote from: Njk on January 12, 2025, 06:54:26 pmOur current kettle has an issue that when even a small amount of lime scale builds in the wrong place it starts behaving like a whistle when its only half way to boiling. A clean out with descaler and it goes quiet again. I'm not sure what it happening, since to far from boiling there shouldn't be much of a gas flow anywhere in the kettle to get such unpleasant whistles started. This kettle is pretty quiet when cleaned out. It has an arrangement at the bottom to break up the fine bubbles that form early, and make many flat bottom kettle chambers quite noisy.

author: valcher
author_rank: Contributor
timestamp: January 12, 2025, 09:33:18 pm
content: Awesome teapot, the nuts and wire in the loop look especially cool

author: Analog Kid
author_rank: Super Contributor
timestamp: January 12, 2025, 09:58:09 pm
content: Quote from: squadchannel on January 12, 2025, 02:04:58 pmWhile we're on the topic of incandescent Xmas tree lights, how about those things they used to sell in the last days of those lights (practically nobody uses them any more, although you can still buy replacement bulbs for the larger sizes), that supposedly would "fix" a string of lights that had gone open-circuit? As I remember they used a high-ish voltage pulse through the string to fuse an open bulb short so the string would light again, or something like that.They actually worked--sometimes. Of course, after that there were fewer working bulbs in series, so the failure rate of the other bulbs would start to escalate.

author: Njk
author_rank: Frequent Contributor
timestamp: January 12, 2025, 11:10:58 pm
content: A guy from ST once visited us to deliver a lecture on the VLIW architecture. He had a nice French accent and in the end all the listeners were awarded with an elegant souvenir flashlight that uses incandescent bulb. A special feature is the replacement bulb, which is hidden deeply inside. Its existence can only be known from the user's manual.

author: themadhippy
author_rank: Super Contributor
timestamp: January 12, 2025, 11:16:51 pm
content: Quoteis it in the endcap cause i thought that was common knolage

author: Analog Kid
author_rank: Super Contributor
timestamp: January 13, 2025, 12:00:07 am
content: I knew about those!My hardware store sold replacement Maglite parts, including those special bulbs with the two wire leads.Micro-halogens, I believe.

author: BrianHG
author_rank: Super Contributor
timestamp: January 13, 2025, 01:12:29 am
content: A 1950's mechanical relay switched, 6v in, 60hz 120v out inverter

author: Njk
author_rank: Frequent Contributor
timestamp: January 13, 2025, 01:40:48 am
content: Quote from: Analog Kid on January 13, 2025, 12:00:07 amYou think so? Looks like an ordinary bulb, measures 0.65 Ohm when cold. Some kind of lens on the light emitting end.

author: Bud
author_rank: Super Contributor
timestamp: January 13, 2025, 01:42:09 am
content: Quote from: themadhippy on January 12, 2025, 11:16:51 pmI burned all spares in mine years ago but recently put an LED replacement into it that I got from Ali. It is amazing how much punch can a single AAA keychain pen light deliver. Blows the original incandescent bulb out of water. And gave my Mag a second life.

author: Analog Kid
author_rank: Super Contributor
timestamp: January 13, 2025, 01:43:15 am
content: I know there are halogen Maglite bulbs, like this one:https://maglite.com/products/replacement-lamp-bulb-for-mag-charger-halogen-flashlightNot sure about those little itty-bitty ones, though.

author: TimFox
author_rank: Super Contributor
timestamp: January 13, 2025, 02:34:14 am
content: The bright incandescent bulbs in MaglitesTMwere often filled with xenon, a heavy inert gas.https://maglite.com/collections/replacement-lamps/products/replacement-xenon-lamp-bulb-for-mini-maglite-2-cell-aa-aaa-flashlight

author: 5U4GB
author_rank: Super Contributor
timestamp: January 13, 2025, 04:20:11 am
content: Quote from: BrianHG on January 13, 2025, 01:12:29 amIsn't that just a vibrator power supply in a hammer-finish case?As an aside, Silicon Chip magazine (AU) has published a few articles on vibrators recently, including various circuits for solid-state replacements for the original mechanical devices.

author: Halcyon
author_rank: Unknown
timestamp: January 13, 2025, 09:21:50 am
content: Quote from: themadhippy on January 12, 2025, 11:16:51 pmMaglites came with a spare bulb in the end-cap wrapped in foam. It was featured in the manuals from the double-cell AA upwards.

author: themadhippy
author_rank: Super Contributor
timestamp: January 13, 2025, 11:16:46 am
content: Quoteno foam on my mini,it has a plastic insert to hold the spare.

author: valcher
author_rank: Contributor
timestamp: January 13, 2025, 12:13:15 pm
content: In the past glow discharge lamps were widely used as reference voltage sources, it would be interesting to compare them with modern semiconductor zener diodes. Has anyone had experience using them?

author: Zero999
author_rank: Super Contributor
timestamp: January 13, 2025, 12:26:59 pm
content: Quote from: Njk on January 11, 2025, 10:32:12 pmWas no attempt made at cancelling the hum? It should be easy to do either inside the amplifier or by an auxilary winding on the virbrator coil into the speaker field.

author: tggzzz
author_rank: Super Contributor
timestamp: January 13, 2025, 06:23:05 pm
content: Quote from: valcher on January 13, 2025, 12:13:15 pmI've had a Solartron LM1420 voltmeter, but I have now sold it so I can't do any serious tests.It used a neon as the secondary reference, with an internal unsaturated Weston standard cell (still in spec, unexpectedly) as the primary reference. My characterisation based onplayingaround alittlebit: the neon voltage was unpredictable, but once the reading was adjusted against the Weston it was stable enough for a 3.5 digit DVM. By that I mean after a week being turned off in a domestic environment, the reading did not need re-adjustment.

author: valcher
author_rank: Contributor
timestamp: January 13, 2025, 07:09:45 pm
content: I have almost never had any experience with tube measuring equipment, but recently I read that the gas tube reference is superior in noise and temperature stability to semiconductor zener diodes.https://jacmusic.com/Sovtek/index.html(at the end of the article)

author: Xena E
author_rank: Frequent Contributor
timestamp: January 13, 2025, 07:52:15 pm
content: Quote from: Zero999 on January 13, 2025, 12:26:59 pmThe output transformers of valve audio equipment that had single ended audio output stages were sometimes given a hum bucking winding, basically a tap that powered the rest of the equipment to cancel the ripple induced hum.

author: Njk
author_rank: Frequent Contributor
timestamp: January 15, 2025, 04:08:42 pm
content: Quote from: valcher on January 12, 2025, 09:33:18 pmIt's not a wire, it's an old bicycle spoke

author: Njk
author_rank: Frequent Contributor
timestamp: January 15, 2025, 04:12:12 pm
content: Quote from: BrianHG on January 13, 2025, 01:12:29 amIt's already mentioned here. The thing for car radio is not a motor-generator, it's more like a vibration pump in a cheap coffee machine

author: Njk
author_rank: Frequent Contributor
timestamp: January 15, 2025, 04:56:48 pm
content: Quote from: Bud on January 13, 2025, 01:42:09 amSeen the pictures and mixed reviews. Seems the thick heatsink disk prevents the reflector end from being fully screwed to the main body part, resulting in poor beam regulation. That's all about using LEDs in such applications. More light but in dumb way. No one cares about beam forming any more. I's bright so it's easy to sell. I would prefer another approach. Keep the old bulb's light amount (call it a gold standard) but improve the beam by better optics and consume less power from the battery to extend the run time. But it's not popular.

author: Xena E
author_rank: Frequent Contributor
timestamp: January 15, 2025, 05:00:19 pm
content: Quote from: Njk on January 15, 2025, 04:12:12 pmFundamental Principles of Vibrator Power Supply Design. Mallory (PDF) 13Mbhttps://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=http://www.tubebooks.org/books/intro_mallory_vibe.pdf&ved=2ahUKEwiV_v3Nl_iKAxWJQUEAHSmtO4EQFnoECBIQAQ&usg=AOvVaw3SwCzbfZEpW9D1TnwaoZZK

author: Njk
author_rank: Frequent Contributor
timestamp: January 15, 2025, 05:07:19 pm
content: Quote from: Zero999 on January 13, 2025, 12:26:59 pmWith a high quality DC the hum is just not there. BTW a permanent magnet can be not so permanent in fact. Those who're restoring old loudspeakers knows that. An old weak magnet can be charged with more magnetism by placing it in the center of improvised winding and using a DC welding machine to pass strong current pulse through the winding

author: Njk
author_rank: Frequent Contributor
timestamp: January 15, 2025, 05:54:03 pm
content: Quote from: tggzzz on January 13, 2025, 06:23:05 pmI had a pulse generator equipped with neon bulb. There were two knobs for pulse amplitude setting, one knob with the scale and the other one for actual amplitude control. User have to set desired amplitude with the first knob and rotate the second knob till the neon bulb became lit (sort of comparator)

author: schmitt trigger
author_rank: Super Contributor
timestamp: January 15, 2025, 11:24:03 pm
content: Love the URSS-era electronic equipment.