Hacking My House #1.5: When Lightning Rings

If you read my last post, you saw my schematic on how to build a musical Arduino doorbell.

After the doorbell was installed, I noticed that it rang by itself sometimes. Not often enough to be too annoying, but enough to think about correcting the issue at some point. I noticed it rang sometimes when a large appliance clicked on, like the dishwasher or central air, and even sometimes when getting a static shock on a light switch.

My annoyance level went through the roof when a large thunderstorm rolled though one afternoon. During the fifteen minutes of thunder crashing, the doorbell rang by itself six times!

So, what was happening, and how did I fix it?

The switch that triggers the doorbell is hooked up to a pin on the Arduino. When the switch is closed, +5V is sent to this pin, and triggers the doorbell music. The minor power fluctuations in my house wiring, caused by large appliances switching on or lightning striking the ground close by were enough to trigger my switch!

To fix, a small filter was added to the switch input to smooth the voltage fluctuations, so it is only triggered when someone really is pressing the button.

The filter consists of a small value capacitor and a couple ferrite toroids. The capacitor goes between the positive and ground switch wires, and the toroids go on the positive wire on the switch.

Doorbell switch filter

After making this quick improvement to my original design, I'm happy to say that I haven't heard any random rings for weeks.

Posted: May 22, 2013