hall-effect
I know little enough about electronics to have to ask basic questions 😛
If I wanted to use a hall effect sensor as a toggle switch what is the minimal circuit that could be used?
Essentially want to put an LED into a badge and use a magnet to turn it on when near but stay on when the magnet is removed. Then turn it off next time the magnet is near and leave it off.
Bias the switching transistor on with a resistor to Vcc, then connect the Hall sensor switch from the Base to the Emitter. The sensor will 'rob' current from the base and turn the transistor off.
simulate this circuit – Schematic created using CircuitLab
You should measure the difference between the blue and yellow cable. If you use a battery (not ground-referenced) to supply the sensor, you can connect the oscilloscope ground to the blue cable and the signal to the yellow cable. You should get some signal in the range of tens of millivolts at least.
Best Answer
Minimal circuit could be one chip like an analogue asic but that would cost many, many thousands of dollars. Minimal could of course mean cheap or small or both. Stretching it a bit, minimal could mean low power.
Putting all this to one side, amplify the hall sensor's output, feed that into a suitably referenced analogue comparator. That will produce a high signal when the magnet is close. Feed that into the clock input of a D type flip flop configured as a divide by two and drive the LED, via a resistor from the output.