Garage door safety sensor hack

[yamanoorsai]

I wanted to use a garage door safety beam sensor in one of my projects assuming that it would have a relay output that would change states when the beam is interrupted. The IR transmitter and receiver has only 2 leads to power them up. There is no documentation on how these things work.

I found a video where I learned that the receiver works like a one wire interface. The transmitter sends in a unique signal and the receiver sends in a PWM signal. There is no documentation available on the nature of the signal expected by the receiver from the transmitter.

I learned that the transmitter sends in a 154 Hz signal at 7.7% duty cycle. This may vary from brand to brand. Has anyone had experience with getting the garage door safety sensor working? Is there any solution to get it working off-the-shelf?

[G7PSK]

Never used a garage door sensor but have used motorised gate sensors and all of them have had an onboard relay. Like these.

http://www.easygates.co.uk/product_info.asp?ProductID=909

[strangelovemd12]

Sorry I can't offer any help, but you've certainly peaked my interest.  Any chance of linking to the resources you managed to dig up?

[RABeng224]

You are on the right track. The reason they're not a simple relay contact comes down to safety. The door opener needs to insure the the safety sensors are operating each closing cycle. A normally closed contact doesn't qualify. Each manufacturer has their own way of doing it. Usually, there are two ways of doing it. Easy way is to power the transmitter and analyze the output of the receiver. Usually the frequency will go down when the beam is blocked. This can be rectified and then you can just monitor the change in voltage. Otherwise, you can actually calculate the frequency in your micro.