5-volt custom electronics

[phrontist]

We have some electronic assemblies that run on 5-volts, and we're trying to figure out the best way to power them while on the robot. Any suggestions? We were going to use a voltage regulating IC connected to the power supply through the breaker board. Is it safe to draw power from the digital outputs? How about 300ma?

[Joe Ross]

http://ifirobotics.com/forum/viewtopic.php?t=71

We are powering our sensors that plug into the digital and analog inputs from those ports, so the voltage reference is the same. Our other circuits are going to be powered off the battery (through the circuit breaker panel, of course).

[phrontist]

Hmmm... Interesting. I know the CMUcam runs off power from the PWM ports, would that be a better option?

[Mike Hendricks]

Originally Posted by phrontist

Hmmm... Interesting. I know the CMUcam runs off power from the PWM ports, would that be a better option?

http://ifirobotics.com/forum/viewtopic.php?t=65



Heh. Some specifics on what youre doing with the electronics (and what you're using component wise) would be helpful.

[Dave Flowerday]

Originally Posted by phrontist

We were going to use a voltage regulating IC connected to the power supply through the breaker board.

If you do use a voltage regulator be careful about the heat it generates. If you're dropping from the 12V battery voltage down to 5 volts, then you're dropping 7 volts across the regulator. Even drawing 100 milliamps from the regulator will cause it to get very hot. You'll want a heatsink to dissipate the heat or the regulator could go into thermal shutdown.

[jgannon]

Originally Posted by phrontist

Hmmm... Interesting. I know the CMUcam runs off power from the PWM ports, would that be a better option?

If you want 7.2V, yes, but then you'd still need a regulator to get it down to 5V.

[Kevin Watson]

Originally Posted by phrontist

We have some electronic assemblies that run on 5-volts, and we're trying to figure out the best way to power them while on the robot. Any suggestions? We were going to use a voltage regulating IC connected to the power supply through the breaker board. Is it safe to draw power from the digital outputs? How about 300ma?

You shouldn't have any problem getting 300mA from the robot controller. If you use the venerable 7805, which is a linear regulator, you'll need to use a heat sink because it'll be dissipating at least 2.1 watts ((12-5)V * 0.3A).

-Kevin

[briholton]

LM7805 in TO220 package (Radio Shack) from a fuse protected 12V source, you've got plenty of heat sink available I'm sure (120 pounds of it), but you shouldn't need much. Careful, the heat sink tab is connected to ground which means you better isolate it from the robot (FIRST rules I believe tell you this is a must). Don't forget an output capacitor, the LM7805 is funny that way sometimes, but other than that, it's solid as a rock. I love talking about my favorite chip, hope you get to use it!

http://www.ugrad.physics.mcgill.ca/Specs/LM7805.pdf