I'd also like your opinion on power supply stuff. I've tried the power supply four different ways:

5v:
- 5v Pololu power supply.
- Arduino VIN gets 5v power from Pololu.
- Betz board gets 3.3v from Arduino's vreg.
- MAX232 gets 5v directly from Pololu, because Arduino's 5v vreg output rail can't supply enough voltage for the MAX232 in that case.
- Heat emitted by Arduino vreg: none.

6v:
- 6v Pololu power supply.
- Arduino VIN gets 6v power from Pololu.
- Betz board gets 3.3v from Arduino's vreg.
- MAX232 gets about 4.8v from Arduino's vreg, but still seems to work just fine.
- Heat emitted by Arduino vreg: hardly detectable.

7.5v:
- 7.5v Pololu power supply.
- Arduino VIN gets 7.5v power from Pololu.
- Betz board gets 3.3v from Arduino's vreg.
- MAX232 gets 5v from Arduino's vreg.
- Heat emitted by Arduino vreg: noticeably warm.

12v:
- No Pololu
- Arduino VIN gets 12v power from Empeg tuner connector directly.
- Betz board gets 3.3v from Arduino's vreg.
- MAX232 gets 5v from Arduino's vreg.
- Heat emitted by Arduino vreg: dangerously hot.

I really like the idea of using a 5v or 6v Pololu for it, since the heat is the least amount. These are for in-car operation and I'd like to think that I'm running all the circuits as cold as I can run them, so that when cars bake in the summer sun there isn't a problem. Right now I'm running mine with the 6v Pololu and it's been working great (not counting the I2S noise issue, which seems unaffected by any power supply changes when I tried that).

The only issue is that the 6v is a hair under the 7.5v that is the expected minimum for these Arduino boards that I'm using. The only drawback appears to be a slightly lower voltage going to the MAX232 chip from the Arduino 5v rail, but that doesn't seem to be a problem for the RS232 communications, it's working fine for me so far. I'm getting about 4.8 volts out of the Arduino voltage regulator in that case, and the specs for the MAX232 chip that I'm using say it can operate at 4.5v.

Any additional opinions on that? How dangerous do you think would it be for me to run 6v for this?
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Tony Fabris