I thought I had a really clever way of implementing 3-volt battery-low detection with only 3 parts: a 2.7-volt reset detector, a resistor, and a capacitor. The idea was to periodically raise and output which will would be filtered by the RC filter, and then feed that to the reset detector. By timing when the reset detector declares the filtered voltage to be above 2.7 volts, I could infer battery voltage. The trouble is those reset detectors (Microchip MCP 130 series) have a built-in additional power-up delay that swamps out the effect of my RC filter.
Does anyone know of any tiny 3-terminal device that acts like a self-contained voltage detector but without any delay? If so, then this method could still be salvaged. I plan on performing an in-circuit calibration on each piece, and then custom-flashing the PIC to compensate for variations in threshold voltage and RC values.
-Robert Scott Ypsilanti, Michigan