Electrical Design Complete

Breadboard circuit and some adapters.
(Click for more photos of this project (photo gallery retired)…)

Well, there it is. The final breadboarding of the RS232 to Eaton Leonard Level Shifter that I’ve been working on. On the breadboard there is the complete circuit, including current reversal protection, but with only one of the indicator LEDs. I ended up changing to using BC557 transistors for turning the LEDs on and off, because the FETs I was originally looking at were leaking current through even when off. I only had one BC557 here, so I just put together one of the circuits and then tried it on each of the lines. It seems to work fine, blinking with data, etc. Its activity should match that which one would see on a PC if using software TX/RX/RTS/CTS activity indicators.

I also played around with sending data through my board to an original Eaton Leonard one, and over a short cable run I had no retries when sending a DOS 6.22 install floppy image at 19.2k via ZMODEM between two HyperTerminal sessions. Since the actual device in production will run somewhere around 3100 baud, this should be good.

I made adapters so that I can easily plug a piece of CAT5 of arbitrary length between the two boards, so I can try to intentionally create unfavorable conditions. Some initial testing stringing an old piece of CAT5 around three fluorescent lamps didn’t show any immediate errors. I’ll do more in-depth testing with this setup over the weekend.

Finally, here is a photo of the stuffed breadboard itself, as I tested it. Now all I have to do is verify the footprints of all the parts I’m using and lay out the PCB. Doing that is fun, and kinda easy. Then it’ll be production time.