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I'm currently toying with embarking upon a totally crazy hobby project, which would prohibit the use of any component that cannot be 100% verified manually: obviously this completely rules out all forms of integrated circuit—even discrete components would have to be manually tested and verified.

On the other hand, it does not rule out the use of pre-made circuits: provided that they can be verified (e.g. following the circuit tracks and testing individual components). It would be a significant timesaver if such pre-made circuits existed for generic tasks typical of basic ICs.

I appreciate that there's pretty much no demand for such circuits (except perhaps at a basic educational level), so imagine that they are not commercially viable. Certainly my searches so far have not uncovered anything.

But do they exist? Does anyone sell generic logic circuits from discrete components?

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  • \$\begingroup\$ Why do you need to be able to test each component individually? Also it may be hard to test a circuit that's pre-built because it will be connected to all sorts of other components so the other components will interact with your discrete component under test. You'll have to unsolder it and resolder it if you were interested in testing it individually. Along the way, you'd have the chance of damaging the component. All in all, why wouldn't you want to build it from scratch? \$\endgroup\$
    – horta
    Commented May 13, 2014 at 14:41
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    \$\begingroup\$ You can open random samples of simple chips and simply inspect them optically. That ought to allow use of SSI and MSI logic chips and any linear ICs, as well as discretes. \$\endgroup\$
    – Spehro Pefhany
    Commented May 13, 2014 at 14:49
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    \$\begingroup\$ @eggyal : aerospace and nuclear project have a high reliability in mind and we don't use only discrete NPN or PNP transistor to achieve the reliability. Also, you may be able to check each transistor individually, but would you be able to do the same for each function ? Or does the complexity will made this impossible ? \$\endgroup\$
    – zeqL
    Commented May 13, 2014 at 15:16
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    \$\begingroup\$ @eggyal: so what level of components are you willing to trust? resistors and transistors? Analog chips (555!), SSI TTL, MSI, LSI, CPLD, FPGA, Micocontrollers? Idem for your tools: are you going to read all lines of let's say the GCC source? \$\endgroup\$
    – Wouter van Ooijen
    Commented May 13, 2014 at 15:28
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    \$\begingroup\$ All of this discussion in the comments seems merely to be me defending/justifying my question. I don't think it has added much to the actual question I have asked (i.e. "does anyone produce such discrete-component circuits?"), to which it seems the answer is an emphatic "no". If someone wants to post that as an answer, I'd be happy to accept. \$\endgroup\$
    – eggyal
    Commented May 13, 2014 at 15:48

2 Answers 2

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You could buy used Digital Equipment (DEC) "Flip-Chip" boards, that were used in the PDP-8 and other computers 50 years ago. They are available on eBay typically for $10 apiece. (Search for "PDP-8 flip".)

There are NAND/NOR gates, inverters, flip-flops, one-shots, decoders -- all built using transistors and diodes. (I believe some newer ones started to use IC's, so you would want to stay away from those.)

These cards were usually plugged into a backplane, and the pins on the back coming from the connectors were connected using wire-wrap. (The linked article even shows the backplane of a PDP-8I.)

Here's a dual flip-flop:

enter image description here

Schematics should be readily available after a little searching.

You could also look into buying a used PDP-8 or other DEC computer in non-working order and get a whole lot of these. Then you would also get the backplane and connectors.

Although wire-wrap isn't used that much anymore, the tools (including wire-wrap guns, much nicer than the little manual wrap tools) are available from Digi-Key and other sources, as well as 30-guage wire-wrap wire.

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  • \$\begingroup\$ This is actually a great suggestion. I will look into it further. Thanks! \$\endgroup\$
    – eggyal
    Commented May 13, 2014 at 17:18
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    \$\begingroup\$ I was about to post a short answer exactly along these lines but some people who cannot understand plain English and/or who insist that people are not allowed to ask questions which are perfectly good technically but that they are not comfortable with for irrelevant reasons have put it on hold. ICs on such systems could probably be opened if desired. HOWEVER, doing this makes it very hard to build a useful product. Better would be top buy a working PDP-8 or similar, verify it as desired, then use it for your purpose. \$\endgroup\$
    – Russell McMahon ♦
    Commented May 13, 2014 at 22:21
  • \$\begingroup\$ @RussellMcMahon I agree, I don't understand why it was closed, I thought it was very clear what the OP was asking for, even if it was a little unusual. \$\endgroup\$
    – tcrosley
    Commented May 13, 2014 at 23:08
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No :D At least not for your application. Possibly small educational ones though. Educational discrete logic circuits are usually not wired up so that the student can learn it through experience.

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  • \$\begingroup\$ They might suffice, then. Especially since it permits testing of the individual components without the problems that you identified in your first comment. But I have not been able to find any such educational circuits...? \$\endgroup\$
    – eggyal
    Commented May 13, 2014 at 16:11
  • \$\begingroup\$ I honestly wouldn't recommend any of the educational kits because they're usually expensive and tailored to doing lots of different things rather than one dedicated thing. They would be extremely expensive for what you want to do since you need tons of components. I'd recommend just buying the discrete components in volume and using lots of large bread boards. In that way, every component will be verifiable by you. \$\endgroup\$
    – horta
    Commented May 13, 2014 at 17:13

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