I'm building a custom BMS (long story - it is necessary - I need to bypass protection circuits to prevent cutout at unsafe moments).
I've got an 8s battery. This battery powers my MCU through a voltage regulator. I need to measure the individual voltages of each cell in the battery.
I had the idea to use a pair of 16 channel analog multiplexers to connect each cell, one-at-a-time, to my ADC.
That idea is unraveling given that my MCU is permanently connected to one end (gnd).
I next had the idea to use a voltage controlled oscillator and opto-isolator... but that too is unraveling (the MUX and the VCO still both need to be powered from that same battery).
Can anyone suggest the best way to solve this interesting dilemma ?
A bit more info - my goal is for the BMS to stay permanently connected - so I'm planning an ultra-low-current regulator and MCU deep sleep. I do want to "wake up" periodically (e.g. once per day) to do measurements, and sound alarms when cells near empty (many months of non-use are likely, maybe a whole year on occasion). During use and charging, I'll be monitoring both charge and voltage, to report SOC and SOH (I plan to support LiFePO4 - so voltage alone is no use for capacity-remaining reports).