Powering the imp

Hi I am setting up 3 imps as multi-sensors utilizing a TC74a I2C chip for temp, a UV detector photo-diode and a not yet designed decibel level sensor. I thought to use the imp as my MySQL db connector by sending a string to a php db insertion script.

I imagine I can power the imp for sufficient periods (1-2 weeks) with a 9v battery running through a LM317 voltage regulator. I hoped to adjust the chip Vout with r1 value of 470 ohm and a r2 value of 1k ohm. That will result in a Vout of 3.91v.

Will the Imp in an April board tolerate 3.91volts as power?

Yes. Both the Mini-USB and solder pads for power supply/battery are regulated to 3.3v before they get to the Imp. Whatever you supply the board with, (in your case 3.91v) will be available at the VIN pin, and 3.3v will be available at the 3.3v pin.

From the documentation:
Power can be supplied using a USB-Mini-B cable from a USB Charger or standard USB Port, though the data lines are not connected to anything. Optionally, a battery connector can be soldered to the battery pads, P+, P-. April can operate from any DC voltage from 3.3 to 17 Volts, and tolerates voltages down to -12 Volts.

So… unless you need to regulate voltage for other chips, just put your 9v into the April board.

You will need to put the imp in sleep mode to get any decent life out of the 9v battery. How often were you planning to sample the sensors?

As jwehr says, just put 9v into the P+/P- pads on the April. It has a switching regulator which is much more efficient than the LM317, especially when coming down from 9v.