Power Supplies

Power is more difficult than I thought

Supplying this project with the right flavors of power is something of a challenge. There are three systems to consider: the fish motors, the sound amplifier, and the raspberry pi.

The fish motors are happiest at about 6 to 7.5 volts and seem to want about 1 watt. The raspberry pi needs 5 vdc (no more, no less) and about 1 watt - more if it is also supplying usb or ethernet. The amp burns about 2 watts. All told, that's about four or five watts.

Attempt #1 - use what's supplied

My original idea was to use the power supply recommended for the billy bass. It's highly unlikely any bmbb you find at garage sales will also have a power supply, so if you go this route, you'll need to find one - the specs are printed on the case - but don't bother going this route - explanation in a second.

The power supply I found supplied 7.5 vdc (at this point, I was unaware I needed to worry about amps) - which was fine for the fish motors - but not so fine for the raspberry pi, which requires 5vdc. Not to worry - I can use the LM7805 5vdc solid-state voltage regulator. Hooking it up is simplicity itself; voltage in, ground, 5vdc out. I breadboarded this up, fed 5 volts to the Raspberry pi via GPIO pin 4 and it booted!

Until the LM7805 overheated and tripped it's internal circuit breaker. The LM7805 handles 1.5 amps, which should be fine for the Rpi - but the power supply was only supplying about 800 ma. Something had to give, fortunately it was the LM7805, which will reset when it cools down.