Rather than adding in a transistor to turn on and off the DHT22, I added in a footprint for a very low power humidity/temp sensor, the
Si7021. I've done my best to follow the design guide and put it on a semi-isolated island of PCB, but OSHPark doesn't guarantee cutouts, so it is a bit of an adventure. It has the same footprint and a the same basic i2c command set as the HTU21D which can be purchased on a breakout board from
Sparkfun if anyone wants to try one out. The price for the sensor from Mouser is only
$4.27, much better than the ~$10 for the DHT22.
I also added in a 3.5mm screw terminal for power, with a solder blob selector to go between using VIN and connecting directly into the 3.3V line, bypassing the voltage regulator (useful for AA battery power from what I understand.) Another addition is a second method for measuring VIN voltage, this time using a design from
JeeLabs. Though I didn't have room for a through hole mosfet without increasing the board footprint, so if you're not keen on surface mount, you'll have to stick with the always on voltage divider.