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The Strangest Computer I’ve Ever Built

COSMAC Face Card.jpg

Lee Hart sent me the guldurndest thing for Christmas: One of his RCA COSMAC CDP1802 Face Card kits. I needed a distraction from a number of things, starting but not ending with publisher disputes. Lee’s Face Card was just the ticket. I haven’t done much PCB soldering in the last few years. Most of what I have done in the electronics sphere was point-to-point, generally on tube circuits. I hadn’t soldered a 40-pin DIP in, well, um…decades?

There’s a knack to it, and I had to dig around a little to find my roll of Ersin .022 Sn63 solder, but after a few minutes’ careful practice it all came back. The kit doesn’t include a 40-pin socket, but I always socket CPUs. The CPU chip I used (see above) has a distinguished history: It was the very same chip I ordered for my original COSMAC Elf project in the fall of 1976. Later it migrated to my second, heavily hacked Elf design (here’s the board mounted on what really was a scrap Xerox 3100 platen cover) with ten banks of CMOS memory (2,560 bytes!) a breadboard block, and a hex keypad. That second Elf board, in turn, became one of two CDP 1802 machines in my well-known robot Cosmo Klein:

Cosmo Klein Color 500 Wide.jpg

Cosmo and I did the SF con circuit from 1978 to the early 80s, and we were actually featured in Look Magazine, as well as an early cable TV program that no one saw.

So I have a certain history with RCA’s peculiar COSMAC architecture, and have built a number of peculiar computers with it. I’m pretty sure none of them were ever quite as peculiar as Lee’s Face Card. Why? The Face Card has no memory, volatile or nonvolatile. It does not run software. Actually, it’s strapped specifically so that it doesn’t run software. (More on this in a moment.) What it does is light up groups of LEDs to make an animated face. How it does this is, well, peculiar: The LEDs are driven from the 1802 chip’s address lines. The data bus is left floating. The 1802, when reset, begins executing code starting at address 0000 in memory. If there’s no memory and the data bus is floating, the chip just executes empty air. The patterns that appear on the address lines aren’t quite random, but close enough so that the LED eyebrows, face, and mouth move in almost random variations. Oh, and the clock speed? One cycle per second.

Peculiar enough for you?

One of the data bus lines has to be pulled high to prevent the binary instruction 00 from executing. This is the HALT opcode, and if empty air delivers 00 to the data bus, the Face Card will freeze and the face pattern will no longer change.

I have special affection for the Face Card because one of the two COSMAC machines in Cosmo displayed an animated face on a portable TV atop his body. Cosmo could look around, smile, frown, and (on a touchtone signal from my 2M HT) lick his chops.

I built the Face Card in about an hour and a half. I’m careful, I work slowly, and I test most components before soldering them into a circuit board. It worked as designed when I turned it on. Theoretically, the system can run on any power source from 4-6VDC. I found that a 5V supply didn’t quite cut it. Some of the LEDs didn’t light fully, and the patterns seemed to get “stuck” now and then. The board has been running at 6V for two days now, and things are brighter and livelier. They’ll be even livelier when I cut the clock generator resistor in half and double the clock speed to two cycles per second.

$19.95 + $5 shipping. CPU socket not included, but I think using one is a good idea.

Highly recommended.


  1. Bob Fegert says:

    In the workbench photo, sitting next to the old scope is what looks to be an old Standard S-RC146A handie!

    That’s the first 2-meter rig I ever owned… takes me back 🙂
    I lived in St Louis and had 34/94 and 16/76 xtals for the local repeaters along with 52 direct.

    I just bought two Baofeng UV-82 4 watt handies from Amazon. Just 34.00ea including shipping and they cover 136-174 & 400-520MHz and also receive only on the FM broadcast band… wow, compare that to what the Standard did and what it cost. amazing

    1. My first 2-meter rig as well; bought it in the fall of 1976 unless I misrecall. Great rig, if huge by today’s standards (as it were) and heavy. I had the crystals you mention plus one pair I ordered for a simplex channel (forget which one) that didn’t have much traffic in my area. I used that for Cosmo’s control channel. I had the TT pad accessory. Cosmo had a 2M receiver that I bought as a kit and may still have. Don’t recall the details but it was one large DIP and a couple of smaller ones. Wasn’t very sensitive but worked very well at close range.

      An HT for 35 bucks. Yow. That’s about $8.50 in 1976 dollars, according to one of the online inflation calculators. The Standard was maybe a *little* more expensive than that, heh. My 02AT still works but I cracked the case some years back and should get me another. The Baofeng would be a low-risk experiment. They have a 2M & 220 variation of the UV-82 (the UV-82X) which would be cool because I have a 220 rig on the shelf that hasn’t seen action in a long time.

      Funny how “dual-band” today means 146 & 440. Back when I learned this business it was 6M & 2M.

      The prices on some Chinese electronics is scary. Android Tablets for $50 etc. I bought a pulsox for $30 plus shipping, and I think they’re even cheaper now.

      1. Bob Fegert says:

        The Baofeng came with the drop-in charger and of course the battery.
        Also included was the belt clip and a combination earphone/mic that seems to work fine although when using it you look like a Secret Service agent.

        The old Standard was so heavy that when I put it on my belt it would almost pull my pants I had to tighten my belt… shoulda just got suspenders.

        I wanted a Motorola handie but could not afford it at the time.

        I do recommend the cheap Baofeng … how wrong can a guy go risking just 35$ I popped it open and there really is nothing much inside recognizable as standard rf circuitry. There is one medium size ASIC and a few teeny rf coils.

        Here is a pic I put up of the insides.

        And have you seen the 7 dollar 40mtr QRP radios from China?
        There are several, this one is 7 dollars and that includes shipping! They actually work, a great buy if you like CW.

    2. Erbo says:

      A dual-band HT for $35 on Amazon Prime? Holy (censored)!

      I managed to roach my Yaesu some time back…somehow, the car charger I tried to use with it must have blown something, and now it won’t power up. This looks like a pretty reasonable replacement, and it costs about as much as I just paid for a copy of Battlefield 4 for Xbox One for my godson’s birthday. I plan to get one at the earliest opportunity.

      1. Bob Fegert says:

        From my original order

        4 of Baofeng UV-82 (Black) Two-Way Radio
        Sold by: WickedSpec
        Condition: Brand New – Always Genuine- 100% Satisfaction. Fulfilled by Amazon

        They seem to have gone up a whole 3$ I knew there was inflation 🙂

    3. Does the UV-82 support T/R on MURS frequencies? MURS channels are on 151 & 154 MHz, which would seem to be in range. Still thinking about the X variant, with 220. If it could do MURS it would be a no-brainer.

      1. Bob Fegert says:

        They transmit everywhere they can receive (except FM broadcast)
        They cover stuff like the Dot channels (MURS) and work very well with the cheapo 2.5khz nfm FRS channels.

        I have used them on the red dot freq.

        There is a FCC type accepted variant that is identical except you cannot change frequencies using the front panel and have to do so using the serial adapter and a PC. These radios are for things like police/fire/etc use.

        I got more than one of these as I am going to experiment with placing one in a weather-tight box and remote mount it inside the skirt of a discone antenna. I think I can use the UV/underground type of CAT 5 to power it and carry digital data. … no expensive coax needed…the cheap stuff is quite lossy at 450. I can put a cheap ARM Cortex0 at the radio end to handle the data I/O. These radios are so cheap that experimentation of this sort is budget friendly. They could also be made into excellent solar powered simplex repeaters.

        1. Just ordered a UV-82, the CHIRP cable and a whip. I’ll review it here after I get it and play with it for awhile.

          Let me know how the remote-mount thing works out if you do it.

          1. Bob Fegert says:

            OK, will let you know about the remote mounting.

            The official serial cable for the Baofeng is the one people like…the cheap knock-offs have driver problems for some.

            You can program from the radio but it is a real pain.

            Be sure to flag out of band frequencies to be receive only 🙂 (I say this for others that may read this…I know you are meticulous)

            I know it’s a technical violation but it’s extremely unlikely anyone would be called on the lack of type acceptance for MURS or GMRS (of course I would never do such a thing myself 😉

      2. Bob Fegert says:

        Jeff, if your interest in MURS freqs is to do something like use them for short-range coms with Carol…like in a mall or similar, then be sure to get some stubbie-duck antennas for the radios. They are available cheap on Amazon and they make the radio very compact so it can fit in even the smallest purse. The stock antenna is a bit longish and works very well but is a tight fit in a purse. I used the radios on Red Dot for this very purpose with my sister in a mall.

        Look for one that covers 144/440 I doubt they have one for 144/220 … but they might.

        Be sure the antenna has a female SMA connector! The radio has a male SMA with the center pin.. some radios are the reverse of this so both antenna types are sold on Amazon.

        This one seems likely

        or maybe

      3. Answered my own question here: The UV-82 can do MURS as well as GMRS…illegally. The problem, as I expected, is type acceptance. You have to be Part 90 to do GMRS, and Part 95 to do MURS. Baofeng has a UV-82C model that is Part 90 certified, so it will do GMRS. As I read it, Part 95 radios have to be locked to narrow-band.

        Still, the UV-82 is attractive for the price alone. I have no radio currently that will do 450, so I may order the UV-82 and see how it goes. For $50, getting a UV-82X later on would not be a big deal.

        All the Baofeng radios program with CHIRP, which is cool.

  2. Rob Duncan says:

    Hi Jeff,
    I doubt that you remember me, but I was at your house in Rochester in Rochester, once. I came with Lee Hart. I seem to recall that you had a robot at that time. My recollection was that you were going to try to teach the robot to find an outlet so it could recharge. I think that there were also discussions along the line of crushing beer cans…

    I have casual followed your writings through the years and recall that I enjoyed your work.

    Best wishes,

    Rob Duncan

    1. Sure I remember you! The weather was ukky in Rochester, but it was a smaller town and didn’t make me feel claustrophobic as much as Chicago and Denver do. And we had a great local nerd group to be part of.

      I didn’t pursue robotics much after we left Rochester in early 1985. It’s a lot easier now, with Arduino and Raspberry Pi controllers going for peanuts. I’ve been writing SF novels for the last ~10 years, which became possible once I retired. I still work the bands as K7JPD, and am working (slowly) on a 12.6VDC distribution system in my shack, ultimately to be fed by a solar array and a husky battery pack. I still have a 1990-era Icom IC-729, and it never got much use in the 90s and still works like new. It was designed as a low-band mobile, but I have it set up in the shack to run (temporarily) on 12V from a minicomputer power supply that I jiggered a little.

      Thanks for stopping by and good luck. I’m still in sporadic touch with Lee. Alas, George Ewing died in 2010, and we miss him.

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