SCELBI RS232 Interface is put in a Proper Package

update 3/24/14 – I have corrected a mistake in the original posting – TX goes to pin 1, not pin 8 – sorry for an confusion that this might have caused

Take a look, it’s a lot cleaner than that bread board implementation that I showed in a previous post. The connections are simple.

  • RX goes to pin 8 of a 86CP11 socket
  • TX go to pin 1 of a different 86CP11 socket
  • Ground goes to pin 11 of the same two 86CP11 sockets
  • Strobe goes to pin 9 of the 86CP11 socket that TX goes to
  • +5V goes to the positive 5 volt power supply terminal
  • SCELBI-RS232
    The enclosure is a Serpac A-20 that I had laying around. The PCB really only needs a 1.5 x 2.5 space to fit, but I had the A-20 enclosure and it makes a nice case for devices that need a DB-9 connector.

    The PCB is single layer, with one jumper wire. This is about as easy as it gets when it comes to etching your own PCBs – single sided and pretty small.


    I etched it using the laser toner method, using glossy paper from a magazine (National Geographic) to make the transfer. The top side legend was done the same way. Put the legend on, after etching and before drilling for best results. I drilled the holes in a drill press with three different drill sizes – #67, 1/32″ and 1/8″. The parts list is pretty basic.

  • 1 2″ x 4″ PCB-??
  • 5 .1 UF capacitors – $.40
  • 1 DB9 connector – $.39
  • 1 MAX 202 chip – $.1.79
  • 1 74LS74 flip flop – $.33
  • 1 Serpac A20 enclosure – $4.56
  • 1 10K 1/4 watt resistor – $.05
  • 1 optional 16 pin socket – $.49
  • 1 optional 14 pin socket – $.45
  • If you have a piece of scrap PCB laying around, like I did, the total cost of parts should be under $10, with over half of that being the enclosure. Actually I had all the parts on hand, and didn’t have to buy anything to build this interface up.

    In the past, I remember marveling when reading magazine and web articles about people building nifty little gadgets with stuff out of their parts box. I would think, how could someone have enough in their stash to do that without buying anything. Well, I guess I’m somehow progressed to the point, where I’ve joined that club.

    Postscript files that can be used to print your own PCB can be found here.

  • Where are the schematics? Well there aren’t any. With a single sided PCB, and only a few components, the art for the PCB is enough to use as the schematics. The RS232 interface side was lifted from a TTL to RS232 converter that I did a few years ago. That converter was largely taken from the RS232 portion of my PS/2 to parallel keyboard adapter.

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