detect movement only one way of elevator arm with two (or three) sensors

Hi, so I am looking for a simple robust way to detect the movement direction of a container elevator on a truck (container washer), when the arm goes up it passes A then B and set a signal on analog/in1 of the GPS modem once so on the backend the elevation shows with time and geoLoc ("container washed"). When the arm goes down passing B then A nothing happens. Then the whole process starts again (with the next container). No RFID tags etc on the containers of course. Microcontroller or relay fine.24V DC. Thanks

Hi
I didn't understand if you can use a microcontroller or not.
However, you can use a 38 kHz ultrasonic sensor, with transmitter and receiver capsule.
The sound generated by the device bounces off the arm and comes back, if the arm is present.
Hi
Giovanni

I presume the "arm" is made of metal. I would suggest using inductive proximity sensor(s). Try starting out here (https://www.digikey.ca/en/products/filter/proximity-sensors/524?s=N4IgjCBcpgbFoDGUBmBDANgZwKYBoQB7KAbRAGZzZZyAWEAy6sABhAF0CAHAFyhADKPAE4BLAHYBzEAF85QA )

You could get away with one and use a divide by 2 circuit but you need to be able to initialise the system and you need to be sure that you don't get multiple edges as the metal moves past the sensor.

It would be better to use two proximity sensors close to each other. Depending which sensor becomes active first would let you know the direction of motion. If you use a micro, then it is simple enough to do this in software. But it is not difficult to do in logic hardware. I would suggest driving a Set/Reset latch, set from one sensor and reset from the other. You would then need a method of holding the latch when both are active, and a delay when either or both go inactive. (just thinking aloud). Also you would need to consider if the edges will have multiple transitions.

This is a simple implementation of a "quadrature encoder". You can Google it.