Paul Kimbrel's Musing

I started building the computer interface on my perf-boards and was tossing around the idea of purchasing a pre-made circuit board for it. I found that Far Circuits had the board available at a pretty decent price, so I decided to go ahead and get it. I also decided to continue the prototype on the perf-board while I waited for the circuit board to arrive. The board came in the mail and I looked at the convoluted mess on my perf-board and decided there’s no test like production.

So I started to solder parts onto the circuit board. I’m glad I did. It saved me a lot of time.

I got it all assembled and went to hook up the potentiometers (oh, I got another one of those ten-turn deals for testing) to the circuit board. But I couldn’t figure out how to get the potentiometer to give me a range of 0-5 volts. After clearing out the cranial cob webs, I found the answer was painfully simple. I had to refresh my memory on how voltage drop across a resistor works. Duh.

Anyhow, I figured it out and got the potentiometers hooked up. I also hooked up some LED’s in place of the future relays. Get the LED’s to light… and I can get the relays to close. I might leave the LED’s in there so I know which relay is being activated.

I started testing and found that all but the “left” direction was firing. After probing around on the voltages, I found that one of the quad-op amps was not putting out the right voltage on one of the amps. I pulled it and replaced it with another one. Let that be a lesson to you kids… always buy twice what you need!

Lo and behold, the left direction lit up. I tried different values on the parallel port and found that potentiometer positions match up perfectly with the requested settings. Yahoo!

Next step… rig up the relays. I’ll be etching my own board for this one!