There are battery operated radios (gas-meters, SCADA...) that are able to get many years out of a battery. I'm guessing they usually sleep and wake occasionally to transmit at full power using big capacitors. I need .75A for .5 seconds, several times a day. How do I go about doing this? (keeping the batteries (AA preferered) less than the size of a pack of cards, no recharging)
A microcontroller can do this. It can keep track of time, using minimal power, and then wake up when required and enable your transmitter.
Some of these (the rfPIC series from microchip, for example) have onboard transmitters that can be used to do the actual transmission, given an antenna.
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Regards,
Robert Monsen
"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.
Uhh... AA alkaline batteries can supply 750mA for 0.5s several times a day just fine. So what part are you having trouble with? It would be helpful to know allot more about what you are doing and what your problem is. What is your application, and what are the relevant voltages, etc.?
3.3V. I tried 4-AA going to a 7805 and it choked. I don't think 8 (4x2) would do the trick either. Do I need to charge a capacitor in order to suplly the 'burst' needed? How?
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A 7805 uses 4 to 10mA of quiescent current already, so that's not the regulator to use when you're after low power. Preferably you should not use any regulator, but there are micropower regulators that don't use much power for themselves.
Jeroen
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