# Measure 12v battery power with Xbee modules

Hello experts
Is it possible to measure multiple slaves remained 12v battery power source with Xbee’s ADC and Digital I/O Line or any method ?
Could you please guide me if it is possible.
Best Regards

Use a ‘resister network’. So if you take two 10,000 ohm resters in series and link this to the 12vdc 7 ground, you will have a fixed load of 20000-ohms (so about 1/2 mA of leakage current always draining your battery).

However, reading the point between the 2 resisters with an Xbee ADC will give you something near 6vdc max. It won’t be 6vdc because the ADC will complicate the resister-network calculation.

I would not do this with a pure battery system, but I run many solar systems with 12v rechargable battery (so really 11.5 to 14vdc) and a solar panel voltage of up to 20vdc. I use a volt-meter to calibrate the reading in software.

Use a ‘resister network’. So if you take two 10,000 ohm resters in series and link this to the 12vdc 7 ground, you will have a fixed load of 20000-ohms (so about 1/2 mA of leakage current always draining your battery).

However, reading the point between the 2 resisters with an Xbee ADC will give you something near 6vdc max. It won’t be 6vdc because the ADC will complicate the resister-network calculation.

I would not do this with a pure battery system, but I run many solar systems with 12v rechargable battery (so really 11.5 to 14vdc) and a solar panel voltage of up to 20vdc. I use a volt-meter to calibrate the reading in software.

Hi Lynnl
Thank you for your quick response.
If i am correct, you mean drop the maksimum voltage on your battery via voltage divider then state this value as reference voltage.
In the datasheet maksimum Analog Input Voltage value is VDD+0,3. so in your example i should drop the voltage from maksimum battery value of 3.3v that this is my reference. If yes i should calculate for this way.
Also could you please let me know what you meant about I would not do this with a pure battery system Do you recommend any alternative/reliable solution ?
Or you mean, should i use external Microcontroller which it has ADC converter to monitoring Battery voltage ?
Best Regards

I was thinking of other hw. You don’t want this external voltage as VRef because you can’t trust its value to be predictable.

As long as your voltage-regulator is accurate, you can use your 3.3vdc power as reference. However, if you expect your product to work even when the voltage regulator can no longer maintain 3.3vdc (battery is low, since the Xbee runs down below 3.0vdc), you can also find a cheap diode designed for voltage-reference use & use a 2.00vdc or 2.2vdc reference.

I am not a battery expert, so can’t really explain how to create a high-impedence ‘battery measure’ circuit which doesn’t drain the battery. It would be rather pointless to add a ‘battery voltage reading’ if it cut your battery life in half! The problem is the current may be low, but it drains forever even when your device sleeps.

I would assume that many online blog/youtube entries talk about a low-drain battery measure on sleeping devcies, and this is 100% unrelated to the complexities of XBee.