So I've just ordered a LiPo battery from a hobby website(Turnigy nano-tech 2200mAh) and I am planning to make a project that has 2 servos(micro) and some leds. So I wanted to power my project with that battery but since they don't come with any overdischarge protection circuits I thought about ordering a seperate protection circuit for the battery, since I only need discharge protection, as I have an intelligent charger and a balancer for the cells. The battery is 7.4v optimal and 8.4 max. But the problem is, I don't know which circuit to go for and is that even a good idea. I'll do some things in the code to save battery power but I need a way for it to cutoff when it reaches a certain voltage so the cells don't get destroyed, since I plan to also use them in my rc car. Also, do I connect the battery to the RAW input on the pro micro or straight to the VCC? Any help on this topic is highly appreciated. Thank you!
Battery of course connects to RAW (the regulator input), not Vcc which is for 3.3V or 5V regulated voltage (depending on which version of the Pro Mini you have).
Here is a circuit that will allow the micro to shut itself down. When you press the button it will take a moment for the micro to turn on D7 to turn the P-MOSFET to power you Arduino. Be sure the Vgs is within range of the P-MOSFET. Not shown is a pull down resistor for the N channel mosfet, a 2N7000 would work. There will be a few uA leakage, this is not a perfect circuit but will do in most cases. When the micro determines it is time to shut down it turns D7 off. This response is to help you get started in solving your problem, not solve it for you.
Good Luck & Have Fun!
Gil
What exactly do you mean with "turn D7 off"?
I believe he means that D7 needs to go high once powered up and then low when you want the power down. I would put a large pull down on the NMOS gate.
Are you sure the individual batteries don't have overdischarge protection built in? Well, if not, then you could add a 2S protection module to your circuit. That would probably require access to the point where the two batteries connect to each other. Does your battery bring out that connection?
A simpler alternative would be to add a way to measure the battery voltage, and then have your sketch read the voltage and shut off the power if the voltage gets too low. Attached is a modified drawing that adds two resistors to divide down the battery voltage to the appropriate range for a 5V Arduino. And since it's downstream from the p-channel mosfet, the divider would sink current only when the power is on. The analogRead() function would be used to read the voltage level.
So if you wanted to keep the battery voltage at 7V or higher to make sure the Nano's regulator works properly, you would look for an analogRead value of less than 860 to shut things down. That would be ((((330/550) * 7 ) / 5 ) * 1024).
