iDoorbell - Arduino powered iPhone notifications

iDoorbell screen shot

Please Note: This project was updated and improved and is described here : iDoorbell v2

I am a software guy and have very little experience with electronics. I am hoping that playing around with Arduino will help me learn a thing or two about resistors, capacitors and the like.

I have started a project using my Arduino that notifies my iPhone whenever a switch in a separate circuit is closed. The plan is to connect this to our home doorbell so as well as the usual ding-dong we also get an iPhone alert. Software-wise this works great using a Wifly shield to enable the Arduino to talk the the Prowl notification service on the Internet over http. It's kind of a wifi version of the project described here

Now the problem I have is how to properly connect the Arduino to the doorbell circuit. The doorbell circuit is powered by a transformer that deliver 5V AC at 1mA. Note AC not DC. I tried measuring the voltage across the transformer using my meter but it read 13.8 so I'm not sure why that is. I want to detect a connection in the AC circuit and notify an Arduino digital input pin. I have been trying to use a H11AA1X optocoupler transistor to keep the two circuits separate. The H11AA1X is designed for AC input as it contains two leds, one for each AC current direction. I connected the H11AA1X in series with the doorbell circuit along with a small 470ohm resistor (to protect the leds in the optocoupler). I also have a couple of leds in the circuit so that I can see when something happens. I have tested the prototype away from the doorbell circuit using a separate (admittedly DC) power supply and simulated the doorbell switch and it works fine. But when I connect it to the doorbell circuit I can not get it to respond to the doorbell switch and the bell itself does not ding-dong.

I now have a working prototype, although I am still a bit worried about the current the H11AA1X is handling.I realised that my original "test" led on the AC side of the circuit was probably a bad idea and removed that. I created a simple circuit with just the H11AA1X and the smallest resistor I had in series with the doorbell circuit. I put 5v across the collector and emitter with an led and a resistor across the DC side of the H11AA1X. When I pressed the doorbell the DC led lit up but the dinger did not dong. I obviously had too much resistance on the AC side to trigger the solenoid. It occurred to me that the bell solenoid is already providing sufficient resistance and that I could probably run the H11AA1X without an additional resistor. So I tried that and it worked. My test meter can't do AC current so I have no idea what current is actually flowing through the H11AA1X. I did find a web site that described the transformer as 1amp, so fingers crossed it will be OK. Here's my working circuit diagram.


I also got it to work by building a different circuit with  the H11AA1X and a resistor in parallel with the bell solenoid. Unfortunately that would entail extra wires and the Arduino to be installed in our hall way which would not pass the wife-acceptance-test. The bell transformer is in our garage so  well out of sight but it does only leave the possibility of connecting my iDoorbell Arduino in series.

I have pushed my iDoorbell code up to github. If anyone is interested in looking at or using my code then click here.


04 May 2013

Hi, I would like to know more about your project and results, can I contact you by email ? thanks Jorge


04 May 2013

Hi Jorge, I'd rather you use the comments system so we can share the conversation with others. What did you want to know more about? Martin