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Topic: Minimizing power consumption (Read 314 times) previous topic - next topic

juanps90

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 !

Jiggy-Ninja

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

polymorph

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?
Steve Greenfield AE7HD
CET Consumer Electronics and Computer
Please don't read your attitudes into my messages

jackrae

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.

CrossRoads

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).

Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

juanps90

#5
Oct 11, 2013, 07:54 pm Last Edit: Oct 11, 2013, 07:59 pm by juanps90 Reason: 1
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!

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