Step 31: Power supply
The RFID allegedly uses "a lot of power" when it is actually in "read" mode. Not sure how much this is but since I am supplying the backlight of my LCD display as well as my RFID reader with 5V power from the on-board voltage regulator on the Mega, I thought it would be best to turn the RFID off most of the time, having it "look" for a new RFID reading every 10 seconds instead.
The Arduino runs at 5V and has an on board voltage regulator to keep everything at 5V. It will run with a DC supply of 7-12V. However at 12V it is converting a lot of that to heat, and if I am also consuming a lot of current with my peripherals, that might not be a great idea.
I therefore have used a stabilised (i.e. not a really cheap thrift shop unit) 7V power supply with claimed output of up to 1.5Amps. By using a 7V supply I have enough to keep the Arduino regulator happy without generating masses of unwanted heat.