My test circuit! I was already well into the design of my proper project and had designed a test circuit. However, I felt that the software for that project was rather complicated and I wanted a simple test program to iron out any problems with the hardware. In the end, the only problems where not due to the circuit itself but me wiring up things wrong (common theme huh- good thing I don't work with pacemakers). However, it was still a worthwhile exercise (and good fun).

The test circuit had three lever switches on it, a PIC (16f84-10) and a seven segment LED. In the end, after much thought, I decided I'd make a basic binary to decimal converter; i.e. press the switches to make a binary number, get the output on the display.

After a few hitches with the hardware (which where quickly discovered), it worked a treat. Nice when it happens like that isn't it!

Below are some pictures of the working unit. I've saved you from the entire 0-7 (000 to 111) collection because after a while they are pretty similar. The first picture demonstrates the LED dimming available on the circuit. This function could be removed for a test circuit by simply connecting the two LED centre pins to the main 5v supply and not bothering with the LM317 and associated resistors.

As it was primaririly a test circuit, I replaced the solenoid relay with a LED and a resistor. This allows me to check when the solenoid should be activated. On the test program, I used it to indicate when the number was odd.

So all in all a succesful test. It did make me realise that LM317s get hot and need heatsinks (ow!) and that consequently, a PMW dimmer function might be a more efficient option. In the end I decided to stick with the LM317 even though it is emitting around 1W of heat. The whole circuit only draws 0.12A (120mA) at 12v so thats good enough for me.

Please note that the circuit is only as big as the orange PCB. The black thing behind it is the 12v 7Ah gel battery that I use for testing my electronics. I didn't make the power leads long enough to bring the PCB to the web cam on it's own!