"Analog Contact Closure" to detect states of another device

A hotel in my town wants me to design a small interactive screen that works alongside their elevator panel. Essentially while they wait for the elevator something plays on a screen, then when the elevator arrives, it says "get in the elevator" or what have you.

I'm communicating with the engineer at long distance and trying to get a sense of how I'm going to interface the screen with the existing panel. He says I will be able to detect state changes from an "analog contact closure." I assume this means simply testing for a closed circuit, but I wanted to see if anyone here could give me a heads up on what I might expect, hardware wise.

"analog contact closure."

This is an unusual and probably wrong or misleading definition.

Get the Engineer to be specific. That's Engineering..

An elevator is not a toy. Take care that later you won’t be found guilty for eventual accidents or malfunction of the elevator. The elevator engineer should provide precise written instructions, how such a device can be added in a safe way to the elevator circuit.

I’d go with a fully independent and non-intrusive device, like a “door open” sensor.

There are a few ways to integrate your unit.
On every floor, there should be a display that shows what floor the elevator is on.
That means there is a central device that 'knows'.

you should be able to use that display on any floor as your interface without any intrusive connections.
no reason you could not add a bar code to the elevator then scan that on each floor.

as others have said, and it needs to be stated with extreme caution. do not attempt to integrate into any part of the elevator. something as simple as shorting a wire might cause it to fail.

there are multiple ways to have an overlay sensor array that can determine what the unit is doing without contact or electrical connections.

If I read you right, you only need to know when the elevator arrives. So can you mount a magnet on the inner elevator doors ( the ones that move with the elevator), and then detect it by placing a hall effect device or a reed switch between the inner and outer doors?


"analog contact closure." I assume this means simply testing for a closed circuit,

I would say you are correct, he will supply you with a pair of terminals that are connected to a normally open switch.
That way you are isolated from the elevator system, you would need to provide switching voltage, but that would be perfectly safe,
Just ask the engineer what the contacts are rated at.
If you are going to use an Arduino then 5V logic will be enough.

Tom.... :slight_smile:

Thanks all.

Firstly, I appreciate the reminders to be very safe. Believe me, I won’t be doing anything that could have an impact on the elevator system whatsoever. The engineer is supposed to provide me with a “read only” way of interacting.

That said, I asked him to verify my suspicion and he said: “our signal will be a dry contact, Rated up to 2 amps current, preferably a 24v circuit, but can accept up to 110v circuit by others. 5v should work thru the contacts as well”

How does one detect a closed circuit on and external circuit? I’m familiar with using a pullup resistor on a single circuit switch, and just checking if it’s been grounded. But how does this work on an external circuit?

Mechanical switches are all alike, you connect and program it just like any other push button. For a longer distance a smaller pullup resistor may be better, i.e. 1k or less. Also the typical 24V operation in professional control would improve the reading of the switch, but for now 5V should be sufficient as well.

As I'm cautious, I'd double check that the recommended switch really is not connected to some elevator circuitry. The contacts should be free of wires, and no voltage should be present on the contacts in open state.

Ah ok, so they are going to provide me with a mechanical switch, as in two pieces of metal that come together at times? And I simply wire one end to a digitalRead on, let's say pin 5, with a pullup, and then to ground? So it's just a run of the mill switch then? I don't know why I thought it would be more complicated, with their voltage running through it and such.