Ok, I’ve done some additional analysis of the power supply, while waiting for the new flash programming device to show up. Here is the situation. The power draw is between .25 and .75 AMPs depending upon whether the motors are running or not. The LM7812 voltage regulator can supply enough power, but it has a specified drop out of about 2 volts. Therefore I need a .75 AMP at 14 volts, DC, in order to supply enough power for this application. The wall wart I was using is rated for 1 AMP at 12 volts. It couldn’t support the .75 AMP at 14 volts. I’ve been looking for a higher power wall wart. I did find a 15 volt 1 AMP surplus unit at http://www.primelec.com for only 2.95 that might work. However after thinking about it, I think it would be better if I could lower requirements a bit. This would allow me to find a more common source for power, such as a 13.8 volt DC supply meant to replace a car battery. I have one of these at home, and it’s not quite up to the job, due to the large 2 volt dropout with the LM7812, even though it is rated at 2.5 amps. In order to solve this, I’m going to investigate low drop out 12V DC regulators. An example might be the LM2940 from National, that reduces the dropout to .5 volt typical or 1 volt maximum. I found another example implementation on the web that used op-amps controlling a FET. The dropout on this design is far less: .1 volt, but it requires a few more parts.

http://www.drbob.net/project/powersupply/linear/12v1alvdfxd/default.html

This is kind of interesting to me, since I’ve had some fun with op-amps in the past.

Now that I know overall power consumption, I also plan to power the 7805, 5 volt regulator off of the 12 volt regulator, instead of unregulated input power. This should lower the power consumption (and heat output) of the 7805.