Door bell sensor?

Hi,

I'm working on a home automation system based on arduino and I'd like to log when by my door bell rings.
My door bell has two bells that are touched by a iron core whenever current passes by a solenoid. Not easy to explain, but the overall idea is that it is a "analog" door bell and produces a lot of sound :slight_smile: .

I was thinking in adding inside the door bell a small piezzo sensor like this

and with some electronics, retrieve the current/voltage when the bell is ringing, and somehow convert it to a digital signal for ~10seconds. With this, I'd be able to detect with a digital port from the arduino that the door bell rang, and log it in a SD card.

However, I didn't have so far any "aha!" idea... I was thinking in connecting the piezzo outputs to a 7805 so I could have 5V in the other end... but I don't even know if it would work...

Anyone with any suggestion or comment?

Thanks in advance,
Joaoabs

I'd try picking-up the electrical signal. Most doorbells run off 12-18VAC. Do you have a voltmeter?

There some issues, but these should be easy to deal with...

  • Everyting is probably "floating", with no ground in the doorbell circuit. You can simply connect the Arduion ground to one side of the dooorbell transformer's secondary.

  • You can't put AC into the Arduino, or voltages greater than 5V. Besides the 12-18VAC, there is a high voltage inductive "kick" from the coil (assuming there's no diode across the coil).

A resistor and a pair of [u]protection doides[/u] will take care of those issues. For additional protection, you can add a voltage divider in front of that to knock the voltage down to 5V. If you use a voltage divider, remember that the peal AC voltage is about 1.4 x the RMS value.

However, I didn't have so far any "aha!" idea... I was thinking in connecting the piezzo outputs to a 7805 so I could have 5V in the other end... but I don't even know if it would work...

No... Voltage regulators are for power supplies.

I think it's generally safe to connect a piezo directly to the Arduino. They can put-out voltages higher than 5V, but they have very high internal impedance (low current capability) and the Arduino has small protection diodes built-in.

Sounds like an ideal chance to build an Arduino powered doorbell...