Control digital input on other device with Arduino


I have a device that accepts digital inputs (NO or NC) that triggers different radio codes. Is it possible to control these inputs with outputs on an Arduino, or do I need a relay? If so, is there any alternative to a relay?

This device also accepts analog inputs (threshold mode / sample mode). Is this the inputs I need to use instead? My Arduino operates at 5V, and the analog inputs accepts max 3V. Is regulating the voltage down my only option here?

What device? What is the equivalent circuit for an input?

It is a commercial device of which I do not have any circuit diagram.

I only know that: "The equipment connected to a digital input works as a switch between the input and ground. If the input is configured as normally open, the input is trigged each time that the switch is closed. If the input is configured as normally closed, the input is trigged each time that the switch is opened."

I can configure the inputs (by using jumpers) selecting whether it should be NO or NC.

I guess I can't just apply voltage here (output HIGH on Arduino)... Is there some way around it, not involving a relay?

If a dry contact triggers an input on the device, you could try a MOSFET (open drain) to see what happens. There will be a need for a common ground.

You could try an opto fet therefore no GND with uld be needed.

What is the current through a contact for activation?


LarryD: You could try an opto fet therefore no GND with uld be needed..

The only thing I had lying aroun was a cuple op 4n35 opto couplers. I tried this, but was not able to get continuity between emitter/collector. If I connect the emitter/collector to a simple LED circuit, it works (that is running the output high for a couple of seconds, then low again), so not sure what happened there...

An opto fet is not the same as a 4N35

You need to find out how low the resistance needs to be before the input considers the connection to GND 'closed'. If you know the highest allowable ON resistance you can choose a mosfet that will work. Try using a 1 k ohm (or lower) pot and start at the high end and lower the resistance until the device sees it as 'closed'. You can of course use small relays but a mosfet might be more convenient.

Operating on resistance is need, as mentioned.

For my H11F2 opto FETs, I get ~300 ohms on resistance.