phone ringer as a switch


I have no idea if this is possible, but, can I somehow use a phone ringer as a trigger to set off a sequence?

I would like to somehow use the voltage that is sent to the phone when it rings as a trigger to initiate movement in a series of solenoids.

Has anyone done anything similar to this?


It should be possible. Use a transformer to couple to the phone line and then a simple rectifier and smoothing cap will give you a DC voltage, then a potential divider to get it into the range to read with an arduino.

However in a lot of countries connecting stuff like this to the phone line is illegal.

thanks for the help both of you!

I may have to check the legalities of what I am planning to do with it then!

I'd have thought you'd be ok if you use an opto-isolator but always best to check.

I have to admit, as soon as I saw the post I instantly thought of IEDs being set off by mobile phones. Oh what a world we live in. Glad your project is completely different :slight_smile:

set off by mobile phones.

Oddly enough things being set off my mobile phones is not illegal as long as the thing being set off is legal but land lines are normally a no no. They are completely forbidden in the U.K.

I believe that there is still laws requiring only FCC approved equipment for attachment to landlines. The way most companies complied with the requirements was to use type accepted modules to handle the landline interface. Search on 'DAA modules' should shed some light on the subject.

One example:

And would it be forbidden to have a some kind of vibration sensor on the existing bell? One that just "listens" to the sound? No electricity involved..

something like Piezo Vibration Sensor - Small Vertical - SEN-09199 - SparkFun Electronics and a couple of resistors to scale the voltage?

Well I know that home made audio couplers (no electrical connection) are illegal (in the UK) without type approval. The excuse they give is the transmit side might be too loud and cause a danger. But even a receive only audio coupler is forbidden.

So if receive only audio couplers are forbidden in the UK ... how about a microphone ? (makes me wonder if people are allowed to listen :slight_smile:

how about a microphone

Yes that's what an audio coupler is.

makes me wonder if people are allowed to listen

People are not classified as equipment. :wink:

People are not classified as equipment. Wink

Really? I know several that are real tools. :smiley:

To keep it on topic: I didn't see any mention that there can be up to about 140V (OK -140V for you sticklers) on a telephone circuit when it rings. So, do observe proper precautions.


Thanks everyone!

I'm in the UK so it looks like the strictest of rules apply to me...