# Minimizing power consumption

Hello, I am trying to build a circuit with a minimum power consumption in order for it to be battery powered.

I have a circuit consisting of a PIR sensor, a 433Mhz transmitter that is turned on or off through a 2n2222a and an atmega328p-pu that is held on power down until the PIR sensor interrupts its sleep. The microcontroller and the PIR sensor are powered from a LM7805, the rf transmitter is connected to 9V. Everything runs on a 9V battery.

I have measured the power consumption and realized that the whole circuit was using about 3.8-4mA during the sleep period ( microcontroller sleeping, 2n2222 not turned on so rf transmitter not consuming power, pir sensor running). Because of such a high power consumption the battery runs out pretty quick, so I was wondering if it would be possible to extend its life by reducing the power consumption even more.

So I have a few questions:

• Does the pullup resistor that is connected to the reset pin have any impact o power consumption
• Would it be possible for a LM7805 to leak a couple mA of current?

Thanks !

Yeah, that's probably all coming from your 7805. 4 AAs will give you 4.5V, which should be close enough for most stuff.

Four AAs will give you 6V, dropping to around 4.5V near the end-of-charge. The Atmel chip is rated at a max of 5.5V.

Yes, the 7805 has a certain amount of current it draws by itself. Change to a low current low dropout linear regulator. What is the power source?

Bias current is specified on the data sheet as 4.3 mA to 8 mA. This is the quiescent current that the unit draws in the idle state. Why are you using a 1A rated regulator to feed a circuit that only demands a few mA. I also suspect you are using one of those silly little 9v batteries (correct ?) Unless size matter, forget about them. If you really want 9 volts, use an R/C rechargeable power pack.

If you really want to use a voltage regulator an LM2936 might better suit your needs. If its output current is too low and you only need a short duration current, you can always use it to charge a capacitor which will provide much higher short term surge current.

Skip the regulator, run the whole thing from 3 AAs, or from a 3.7-4.2V Lipo, and slow the clock down to 8 MHz.
This remote control is similar. Uses a 8 MHz promini that goes into powerdown sleep mode, wakes on a button press, reads the keypad using Keypad library, sends it via 433 MHz Tx with Virtualwire library, goes back to sleep.
Debugged with 3 AAs, runs now from 1000mAH LiPo under the board.
Recharge controlled by MAX1811 (not shown, goes in the empty 8 pin socket with a couple Rs & Cs), recharges from 5V source (which can be USB port).

Thank you for all your suggestions. I was already running the device with no crystal and using the internal 8mhz oscillator.

Will the LM7805 still leak current if applied +5V to the out pin and keep gnd connected, leaving the IN pin floating?

I am using one of those little 9V batteries because they provide 9V in a reasonably small package. The reason for using a power source of more than 9V was to increase range of rf transmitter.

Thanks!