Interpreting old schematic  - Page 1
Forum section: electronics / beginners

author: Hesswelder
author_rank: Newbie
timestamp: July 16, 2023, 12:59:22 am
content: So I want to start off by saying that I am still a newbie for the most part but I have been building synth circuits from schematics for awhile now.I have stumbled on this pdf for a speech synthesizer from a "Wireless World" magazine 1978. I would like to build it, but I am having some trouble interpreting some aspects such as legibility of numbers and certain connections marked with asterisks.Attached is a schematic made from the pdf trying to be faithful to the original and with my best judgement, it is a sort of pictorial representation. Some Notes about my drawing; nets are color coded for readability, variable resistors are represented as a pot wired as a rheostat, use of two TL074s instead of 471s, omitted Lm380+speaker. I'm also a bit concerned about using an 18v power source (two PP3 batteries) as stated in the pdf because of how some chips are only rated at 15v max.I appreciate any thoughts or insight. I apologize if this isn't posted in the correct forum.

author: ledtester
author_rank: Super Contributor
timestamp: July 16, 2023, 01:17:01 am
content: Quote from: Hesswelder on July 16, 2023, 12:59:22 amAccording to this datasheet:https://www.ti.com/lit/ds/symlink/tl074.pdf?ts=1689441725071the TL074 in the PDIP package ("N" suffix) can handle a supply voltage of up to 42V.Btw - you can find somewhat better scans of those articles here:https://worldradiohistory.com/UK/Wireless-World/70s/Wireless-World-1978-12.pdfhttps://worldradiohistory.com/UK/Wireless-World/70s/Wireless-World-1979-01-S-OCR.pdfAs for verifying your layout, I would consider using a circuit design program like KiCad. Once you enter in your schematic such a program will make sure that your wiring matches your schematic.

author: Kim Christensen
author_rank: Super Contributor
timestamp: July 16, 2023, 03:35:05 am
content: Quote from: Hesswelder on July 16, 2023, 12:59:22 amThose connections should normally be sitting at logic low. Bridging a "touch switch" with your finger will make the corresponding connection go logic high. Probably not the most static immune circuitry there.QuoteIf you use the4000Bseries from TI, they are rated for 18V operation. Or you could simply operate this circuit from 15V if you wanted.Pin 10 of righthand TL074 is floating.

author: floobydust
author_rank: Super Contributor
timestamp: July 16, 2023, 04:52:15 am
content: It looks like an interesting project.Always search for corrections, errata etc. with old projects. I found this Wireless World 1979-02 which fills in a few gaps in the schematic.edit: I think OP's new schematic already has this.

author: fourtytwo42
author_rank: Super Contributor
timestamp: July 16, 2023, 10:52:06 am
content: Quote from: Hesswelder on July 16, 2023, 12:59:22 amI don't know anyone who would draw a schematic like that, it's functionally unreadable & unusable IMOP.

author: DonKu
author_rank: Regular Contributor
timestamp: July 16, 2023, 02:00:43 pm
content: Quote from: fourtytwo42 on July 16, 2023, 10:52:06 amIsn't it wild?

author: ledtester
author_rank: Super Contributor
timestamp: July 16, 2023, 03:06:21 pm
content: Quote from: DonKu on July 16, 2023, 02:00:43 pmIt's a wiring diagram - more akin to a PCB layout.

author: StereoAmateur
author_rank: Newbie
timestamp: July 17, 2023, 01:17:51 am
content: Quote from: fourtytwo42 on July 16, 2023, 10:52:06 amAs someone who has a much easier time reading schematics with varying colors, and doesn't have any issue parsing the structure of the schematic, I resent this "there is only one right way" attitude. You're free to do your schematics "the right way" but I don't think you need to be coming into people's threads just to tell them you don't like how their brain works.

author: Ian.M
author_rank: Super Contributor
timestamp: July 17, 2023, 02:30:52 am
content: PCB layouts and wiring diagrams are useful but aren't schematics.If you want feedback from the pros for free, you need to draw your schematics in the style they like, because it makes it easier to comprehend the circuit's function. See:https://www.k-state.edu/edl/docs/pubs/technical-resources/Technote8.pdfGoing too far the other way and using net labels for all interconnections instead of drawing the wires is also undesirable, and will get the pros grumbling they "asked for a schematic, not a netlist"!The cherry on top is that the O.P. saved it as a JPEG - a lossy image format known to cause artefacts where high edge contrast lines cross or where fine detail is present near the boundary of a large area of the same (or similar) colour. This specifically affects schematics because the artefacts often make it unclear whether the crossing lines are separate wires or joined and can result in loss of decimal points in component values. For %DEITY%'s sake use an image format with lossless compression when posting schematics e.g. PNG or GIF.All-in I'd say the O.P. lost the attention of >90% of the experts here, including the grey-beards who probably remember reading the original magazine before they spent more than ten seconds looking at the O.P's 'schematic'. The article however did make decent coffee break reading!

author: schmitt trigger
author_rank: Super Contributor
timestamp: July 17, 2023, 02:53:28 am
content: Quote from: StereoAmateur on July 17, 2023, 01:17:51 amYou are absolutely right, but… but…there is always a but, isn’t it?But if you come to a forum seeking assistance, the least one can do is to simplify the task of the people you are requesting the help from.There is a reason for drawing schematics a certain way. The reason is that the signal flow can be followed by people unfamiliar with the circuit. As drawn, the signal flow is very confusing, due to the spaghetti signal path.I am not criticizing the use of wire colors. I like that.

author: SmallCog
author_rank: Frequent Contributor
timestamp: July 17, 2023, 02:59:18 am
content: That's the sort of diagram I work from at workCommon in electrical / automation type industries

author: EPAIII
author_rank: Super Contributor
timestamp: July 17, 2023, 03:36:17 am
content: I also am a big proponent for well drawn schematics.Go with the flow: left to right and top to bottom. Inputs on the left and outputs on the right.DON'T try to convert them into "pictorials": use schematic symbols.And when an IC has multiple circuits, like several amps or digital functions, DON'T insist on keeping them inside one rectangle. Put them where they need to be in the flow of the circuit and tie their physical grouping in one IC package with the component numbers (U3a, U3b, U3c, etc.)Finally, except for power and ground, keep the use of disconnected tie points to a minimum. DRAW the circuit paths. And use the above "rules" to keep them as short as possible.A schematic is a way to transmit to the viewer HOW the circuit FUNCTIONS. Not how is will look when assembled or where the various elements are physically grouped into plastic/ceramic packages.Quote from: fourtytwo42 on July 16, 2023, 10:52:06 am

author: EPAIII
author_rank: Super Contributor
timestamp: July 17, 2023, 03:47:39 am
content: Well said. I, for one, will say that there is NO WAY that I am going to spend two to four hours straightening that schematic out in order to understand it and see if it looks as if it will work. Perhaps someone here will, I don't know. But IMHO, the OP should be the one to do so.Or just breadboard it and see what happens.Quote from: schmitt trigger on July 17, 2023, 02:53:28 am

author: ArdWar
author_rank: Frequent Contributor
timestamp: July 17, 2023, 03:47:51 am
content: Quote from: SmallCog on July 17, 2023, 02:59:18 amThose kind of wiring diagrams are fine for field works, where operators only need to know how to wire/connect the devices correctly.It is terrible to figure out circuit "flow" however. Most people usually rely on pattern recognition. Draw the classic 2 BJT astable multivibrator in anything other than the usual "X" pattern and you probably need a good ten seconds figuring out what's going on.

author: fourtytwo42
author_rank: Super Contributor
timestamp: July 17, 2023, 11:22:09 am
content: Quote from: StereoAmateur on July 17, 2023, 01:17:51 amActually I came here to see if I could help the OP but found the "schematic" impossible to use as did many others. I suggest if you want help with something you make it easy for people to help you, simple psychology right

author: Terry Bites
author_rank: Super Contributor
timestamp: July 17, 2023, 01:25:42 pm
content: Cool project. I was an avid reader of WW throughout the 70’s I must have missed this one. Bringback WWI think I would have loved to have built this.I am looking at the original article on a 24-inch monitor and I can only see one illegible resistor value inspite of the crap phocopying.Its just a pull up on a cmos gate, I don’t see why that cant’ just be tied to V+, but 10k will do fine.It looks like it was a lot of work to create your wiring diagram, you might have done yourself a solid and learned some CAD, eg Kicad or Eagle.If you want to make a modern PCB you’ll need to use schematic capture driven CAD. The parts are all common library items. I’d keep it historically correct and go through-hole not sm. I'm tempted to do just that, I'm having a slow day....

author: floobydust
author_rank: Super Contributor
timestamp: July 19, 2023, 05:54:14 pm
content: OP, the power wiring is not right. I think the two 9v batteries are series-connected with the midpoint connected to circuit GND. That is, making a +9V/-9V supply for the op-amps which require that for audio AC. The op-amps cannot run off a single-supply i.e. 18V yet be biased at GND.The CMOS digital logic would run from only +9V and GND.The CMOS switch CD4016 would need +9/-9V as it switches audio, but then the control pins it would need a -ve voltage and I do not see that coming from the touch switches. Not sure how that portion works.Audio power amplifier LM380 or LM386 is fine with single supply from +9V. EDIT: LM380: 10V-22V, LM386N-1,-3: 4-12V, LM386N-4: 5-18VAlso missing are decoupling capacitors on power like 0.1uF and 100uF. Power on/off switch would be DPDT. I also put reverse-diodes 1N4002 across the 9V and -9V rails in the case only one battery is connected/alive and it does not cause the other rail to go reverse-polarity.It's difficult because the original schematic is vague and relies on common assumptions. I would question power +/- and ground for the IC's.But the project is an interesting take on speech synthesis. The author did more R&D on that, he got a Ph.D. on it. I would say it's worth getting going.

author: Terry Bites
author_rank: Super Contributor
timestamp: July 25, 2023, 06:24:22 pm
content: FAO Hesswelder.....so two questions. Can you attach files in messages? What happened to spell check? Firefox has it enabled but it doesnt work on the eevblog, any ideas.

author: Clear as mud
author_rank: Regular Contributor
timestamp: July 26, 2023, 01:46:44 pm
content: Quote from: ledtester on July 16, 2023, 03:06:21 pmI like it as a wiring diagram. I would like to know what software OP used to make the diagram. It would be useful for making car or motorcycle wiring diagrams. You get the diagrams in the factory service manuals, but they don't usually have colors, so it would be nice to make diagrams with colors that match the colors of the wires in the car.I made a car wiring diagram like that once, but it was so long ago I don't remember what I used. It might have been SmartDraw, way back when that was $29 shareware instead of $2,900.00.

author: Clear as mud
author_rank: Regular Contributor
timestamp: July 26, 2023, 02:09:40 pm
content: Terry,Firefox spell check is working for me.Spll cheque is wroking fpr mee.The above line has almost all the words with the crinkly red underline that Firefox adds to indicate misspelled words.

author: Terry Bites
author_rank: Super Contributor
timestamp: July 26, 2023, 03:11:23 pm
content: I did it on some old banger 80's software called vutrax. Its free these days.spell check mystery unsolved.

author: Hesswelder
author_rank: Newbie
timestamp: July 26, 2023, 05:53:29 pm
content: I used MS Paint for the diagram lol.

author: m k
author_rank: Super Contributor
timestamp: July 26, 2023, 06:57:10 pm
content: Dedication.

author: DavidAlfa
author_rank: Super Contributor
timestamp: July 26, 2023, 07:13:52 pm
content: Interpret this. What a weird representation of BJTs they used in the 60s!

author: vk6zgo
author_rank: Super Contributor
timestamp: July 27, 2023, 12:33:43 am
content: Quote from: DavidAlfa on July 26, 2023, 07:13:52 pmIt was going to be "the new standard" for representing BJTs, according to some authority or other.I remember "Electronics Australia" adopting it, & battling on with it for years, whilst just about everybody else ignored the idea & stuck with the old type symbols.I only ever saw it used by one manufacturer in that time.Eventually EA had to admit that they were "the only ones in the parade in step" & return to the old style.

author: Ian.M
author_rank: Super Contributor
timestamp: July 27, 2023, 12:57:12 am
content: If you are used to valve schematics of that era and know your European transistors (mostly Philips and Mullard devices), its easy enough to read. A schematic that uses ANSI/IEEE rectangular or %DEITY% forbid DIN symbols for simple LSI gates (rather than ANSI/IEEE distinctive shape symbols (US traditional/military)) is *FAR* harder to read. (ANSI/IEEE rectangular symbols are preferable for more complex MSI logic.)