I'm designing a circuit to monitor the voltage of a Li-Po battery (single cell 3.7v, 2500mAh, 25A) and switch off the battery when the voltage drops to a certain threshold. The Circuit will also pulse an LED to indicate the Battery needs to be recharged.
The ATtiny85 will be programmed to monitor it's internal Vcc voltage and turn on the MOSFET if the battery is above 3V. When the battery is below 3V it will turn off the MOSFET and pulse the LED every couple of seconds. The micro will use sleep mode to reduce the battery drain of the monitor circuit.
Does this seem like a reasonable circuit to accomplish this task? Is the value of R2 reasonable? (not sure how to calculate this value) Can the ATtiny85 maintain the output on PB1 when it's in sleep mode? What kind of parasitic losses on the battery does the use of the MOSFET introduce?
Also, as the battery voltage decreases the voltage driving the gate (PB1) will decrease as well. I don't think this is a problem but not sure.