I'd like to have a switch activated when something gets near it. Today it's just a pushbutton, that's active as long as it's depressed.
I'm going to use an analog ultrasonic ranger, using its analog output. What I'd like to do is have an analog circuit activate a mosfet when a certain range threshold is hit. My question is - how do I make this "binary?" How do I have Vgs applied to the mosfet when the analog voltage on the ranger crosses a specific value? I thought about using a zener diode with the breakdown voltage at the distance that I need (the threshold I'm looking for is about 10" away from the device, which translates to ~100mV on the analog pin). Given the low voltage the sensor will output at that distance, I assume a zener won't work.
I'd like to not involve an MCU if possible, because I'd like this to be a simple drop-in.