Here's the scenario: I have a mini robot controlled by a digispark (ATTiny85) that moves via 9V motors. Power comes from a single 18650 cell. I use a step-up converter (MT3608) to boost the voltage up to 9V, and this is then supplied to the Digispark's VIN pin as well as a PWM controller (L9110). This all works with no problem.
When the battery voltage is low (measured from the battery directly to an analog input pin), the robot returns to a docking station. The dock charges the 18650 using a TP4056. Again, there is no problem here.
However, I can't figure out how to detect when the battery is fully charged so that the robot can move away from the docking station. The primary issue is that the current draw of the digispark, even with no power to the motors (and, indeed, with the PWM controller unplugged) is still to high to ever allow the TP4056 to ever send a STDBY (fully charged) signal. I am sure the issue is the digispark since, if I disconnect that from the power supply, the TP4056 successfully supplies the fully charged signal (even with the PWM controller plugged in).
I've tried removing the digispark's power LED to reduce consumption, as well as supplying power to it directly from the battery instead of through the step-up converter, but the TP4056 still doesn't co-operate.
So, does anyone have ideas on how I can either reduce the digispark's power consumption when charging (while still being able to monitor the charge state), or finding an alternative way of measuring fully charged battery (or close to it) without using the TP4056's STANDBY signal?