adcbatteriesmicrocontroller
I'd like to estimate the remaining battery life of a battery that powers a microcontroller. Could I accomplish this by simply leading the battery into the MCU's built-in ADC?
My idea is that I could plot the voltage over time to figure out how much battery life remains. But would the change in voltage be noticeable? And would it be a problem that the same battery powers the MCU (and ADC)?
The Microchip dsPIC motor control DSCs support micro-stepping (down to 1/64 of a step):
http://ww1.microchip.com/downloads/en/AppNotes/01307A.pdf
Closed loop current control is supported.
There are various options, one reasonably simple circuit is this (bias/filter caps and bias voltage circuit not shown for simplicity):
Simulation:
For both graphs the x axis shows the input voltage - top graph is the input voltage itself (not necessary really), and the bottom graph is the output voltage versus the input voltage.
Note that the circuit inverts the signal, so 1.8V = 7V in and 0V = 16V in, but this is easily dealt with in a micro.
The circuit divides by 5 and shifts so the 1.8V span is between 0 and 1.8V. To learn how to calculate and design such circuits, OpAmps for Everyone is a good free book to start with.
Best Answer
You can do this (assuming voltage is a predictable function of remaining life, but that's another issue) as long as there is a fixed voltage reference available in the system somewhere. Some micros have a fixed voltage reference built in, which can usually be read by the internal A/D or applied as the A/D scale. If not, you have to supply some external reference. Note that due to power consumption you may want the micro to switch on this reference only for a short time around battery readings, which don't need be very often relative to the time it takes to do a reading.