You can get '328P (pico power) $2.08 qty 10+http://www.mouser.com/ProductDetail/Atmel/ATMEGA328P-PU/?qs=K8BHR703ZXhdUS2n3IW%2fRITwfrPGjO%2fc8 mhz xtal $0.17 http://www.dipmicro.com/store/index.php?act=viewProd&productCode=XC6-80000Run at 8 MHz to save power, get max life out of the batteries.2x 22 pf cap $0.05 http://www.dipmicro.com/store/C1K22-10003x 100nF cap $0.05 http://www.dipmicro.com/store/C5K10-5010K resistor $0.02 http://www.dipmicro.com/store/R4J10-8perf board to build it up on $0.30 http://www.dipmicro.com/store/PCB-UNI7Hsocket for uC $0.17 http://www.dipmicro.com/store/ICS328header strip to connect sensors to $0.18 http://www.dipmicro.com/store/HEADS40GAAA battery holder $0.577 http://www.dipmicro.com/store/BHAAA3WTotal: <$4 for qty 10-12 units
If you are going to run small Transmitters and microcontroller off batteries, its critical to look at the powerconsumption of what you are running, otherwise you will be replacing the batteries every week.This means running the microprocessor in ultra low power consumption mode, and running the transmitteras infrequently as possible.For example, the little transmitter you are considering, draws 8 ma when transmitting.Running this off a 9V battery, if its a small transistor radio type battery will drain the battery in just 12 hours.Even running the Transmitter for just 1% of total time will drain the battery in just under 2 months.Its critical to minimise battery consumption which means using the lowest possible supply voltages and keeping the transmitteron time as low as possible.Id be looking at running off 3 V which you can get from 2 AA cells in series, using the highest data rate you can manageand thoroughly understanding issues like manchester coding,CRC error checking, and microcontroller power management.Also, the frequencies that these small transmitters use , are commonly used by many common household appliances like garage door openerscar entry systems, wireless door alarms, wireless security systems etc so you must be able to recognise your data from everything else thats around.The better transmitters like the Xbee use 2.4 Ghz and do all the hard work for you, which is one of the reasons they are more expensive.They also draw 45 ma which means close to useless for running off batteries, unless you use a car battery.
Or go with larger batteries, like C or D, lot more capacity. If you can live with a little more bulk.
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