Finished the LiPo charger module schematic!

I had some problems making the battery balancing circuitry because I didn’t know how to switch the balancing mosfets without frying the microcontroller. The problem was that the ground reference for the microcontroller and mosfets were different that basically means that for example the mosfet connected for balancing cell 3 of the battery will have its reference from cell 3 of the pack but the microcontroller will have its reference from the negative of the pack (cell 1) so for the mosfet its source will be at 0V (gnd), but for the microcontroller the mosfet’s source will be around 10.8V. That will mean if I try to turn on the mosfet with 3.3V from the microcontroller Vgs would equal -7.5V (3.3V - 10.8V) which means the mosfet will not turn on since for an N-channel mosfet Vgs has to be positive (atleast 2V for the one I used). First I wanted to use a P-channel mosfet to connect the positive side of the cell to the gate of the N-channel mosfet that would turn on the N-channel mosfet since Vgs would be around 3.6V (3.6V - 0V)
but when the balancing mosfet will be off the P-channel mosfet’s gate will be pulled up to the cell voltage so for the mosfets its around 3.6V but for the microcontroller around 10.8v for cell 3 that will fry the microcontroller.
Instead I used a octocoupler to connect the positive side of the cell to the N-channel mosfet. Like this I can turn the balancing mosfet on without having the high voltage on the pin of the microcontroller.

That probably wasn’t a very good explanation. I’m not very good at explaining.

Expected features of the module:

• Supports charging 1-4S LiPo and Li-Ion batteries
• Max charge current: 5-6A (1S), 4-4.5A (2S), 3A (3S), 2A (4S)

If you actually read through all of this, thank you!