# Wireless transmitters (pic16f1825 has a 5 bit DAC)

#### Ian Rogers

Joined Dec 12, 2012
800
On my wireless transmitters I use 3v batteries... I then connect a voltage divider consisting of 2 10k resistors to the battery terminal to ground and read middle... BUT!! I use and internal reference of 1.5v.. (pic16f1825 has a 5 bit DAC) My system needs 1.8V to function so my percentage is 1.8v -> 3.2v. I just read the voltage which should be 1.5v max to 0.9v min.

#### upand_at_them

Joined May 15, 2010
475
On my wireless transmitters I use 3v batteries... I then connect a voltage divider consisting of 2 10k resistors to the battery terminal to ground and read middle... BUT!! I use and internal reference of 1.5v.. (pic16f1825 has a 5 bit DAC) My system needs 1.8V to function so my percentage is 1.8v -> 3.2v. I just read the voltage which should be 1.5v max to 0.9v min.
You can simplify this *and* use less power by reading the internal fixed voltage reference, which will of course give a result dependent on your Vdd (the battery). Use a lookup table to return the result. Microchip have an app note about it, including calibration.

#### Ian Rogers

Joined Dec 12, 2012
800
ou can simplify this *and* use less power by reading the internal fixed voltage reference, which will of course give a result dependent on your Vdd (the battery). Use a lookup table to return the result. Microchip have an app note about it, including calibration.
True.... But nowadays I throw a solar panel on and charge a lithium cell... Never needed to monitor the battery since..

#### upand_at_them

Joined May 15, 2010
475
True.... But nowadays I throw a solar panel on and charge a lithium cell... Never needed to monitor the battery since..
What circuit are you using for charging?

#### Ian Rogers

Joined Dec 12, 2012
800
What circuit are you using for charging?
Microchip MIC79050 Quite efficient and has worked well for the last few years..

#### upand_at_them

Joined May 15, 2010
475
I'll check it out. Thanks. I want to put something wireless on my roof.

#### Ian Rogers

Joined Dec 12, 2012
800
We also use the MCP73831 when using the larger 18650 batteries... As these will last months without sunlight, then they charge quite rapidly... We use the SOT version Only a prog resistor and two external caps needed

#### upand_at_them

Joined May 15, 2010
475
Ian, are you using a charge controller? I'd be worried about weird charge effect, or poor charging, due to clouds-sun-clouds-sun... Any problem with that?

#### upand_at_them

Joined May 15, 2010
475
Oh, I see that the MCP73831 is a charge controller.