Hi everyone, I am new to the forum, but I'll try to jump right in here. I have been working on a remotely controlled minibot based on the Wild Thumper platform, and all that's going well enough. I was just trying to implement a system for monitoring battery life on my Mega 2560. I have been using the DF Robot 7.4V LiPo battery packs (7.4V Lipo 2500mAh Battery (Arduino Power Jack) - DFRobot), but I have been having trouble trying to find a good way to monitor voltage at the Arduino's power jack.
As I understand it, the Vin pin and the power jack share a junction (i.e. will have the same potential), so would there be anything wrong with the idea of redirecting current through the Vin pin to the voltage divider? It appears to work, but I just wanted to clarify that it won't result in any damage to the Arduino itself since technically I am directly current out of an input pin.
Thanks in advance!
the Vin pin and the power jack share a junction (i.e. will have the same potential),
Incorrect - there is diode D1 between them.
http://www.arduino.cc/en/uploads/Main/arduino-mega2560_R3-sch.pdf
So Vin will be 0.5V to 0.7V less than the barrel jack.
Otherwise, keep the resistor value total above 10K to not suck too much current themselves (<1mA). An analog input will only draw 1uA as long as the voltage is <= 5.5V.
If the voltage is greater than Avcc (= Vcc for standard setup) then >=5V will return 1023.
Ahh I see, now that I have checked the battery itself its appears that just under 0.8V is dissipated before reaching the Vin pin (presumably there are some other minor internal resistances in play here).
My voltage divider uses a 10K and a 1K resistor as of right now, so presumably that's ok. I think I may move to a smaller voltage step-down (i.e.e 10K-10K divider) in the future.
Do you have any other suggestions for how I might establish a solid connection with the battery pack without messing around with the Arduino barrel jack connection?
I suppose the alternative would be to just do my battery testing with the knowledge that ~0.5-0.7V is lost through the diode. My plan is that eventually I can use some math to map the non-linear relationship between Voltage output and remaining charge to create a battery life indicator.