voltage-specific relay-- Is there such a thing?

[Matt65000]

Hello, I'm new to this site and somewhat new to practical electronics (although I'm pretty solid on the physics of it all.) Here's my problem: I need a device that functions like a relay switch. However, instead of responding when it receives any voltage (within its specs), I need a relay that will respond only when it receives a very specific voltage, or a narrow range of voltages. It should not trip if it receives a voltage out of that range. Does such a device exist? If not, is there a way I can make one? Thanks very much.

Here are more details about what I'm trying to do: The steering wheel in my car has 6 switches in it that control various aspects of the radio. All 6 have a different resistor value associated with it and lead to a common output wire to the radio. The processor in the radio determines which switch was thrown by the voltage or current that it reads--which will be different for each switch due to the differing resistors. I'm trying to commandeer one of these switches to operate an air horn....

Thanks very much for any guidance.

 

[MikeMl]

Can you provide some numbers? e.g., I want the relay pulled in when input is greater than X but less than Y. What are X and Y? You need to provide some measured values.

Supply voltage, nominal automotive 14V?

Relay contact current?

 

[Diver300]

I think that what you a looking for is a called a "window comparator". It basically consists of two voltage comparators so that the output turns on at one voltage and turns off at a higher voltage. You would probably also want a small time delay so that you don't get the output operating briefly when the voltage goes from value below the required one to a value that is above the required one.

You should also make sure that the reference voltage for the window comparator is the radio that normally reads the resistance. That is because car systems can be quite noisy, and small voltage differences could make the wrong button be seen as the horn.

 

[shortbus=]

Or you could use the regular horn activator(switch) and a SPDT, single pole double throw switch in or under the dash to select between regular horn and the air horn. That's how my grandson did it on his Chevy pickup with a Duramax diesel.

 

[Reloadron]

With the very basic information you provided I would start looking towards as Diver300 mentions, a Window Comparator.

Ron