Thank you so much. It was indeed trying to pull down the power supply. I wa= s able to read a clear signal now: http://imgur.com/BnqZvwm Did the protection circuitry of the power supply cause the problem I was ha= ving? Sai On Friday, January 3, 2014 4:59 PM, Steve Smith wr= ote: =20 This looks like the same two wire system I have seen on thermostats with remote sensors... they send data over power...=20 You can do this by placing a small resistor in one of the supply lines say 10-100R and then you will get a signal larger than 20mV you can feed this into a comparator within a pic using either a FVR check the spec you will probably need to select the resistor to give greater than 600mV of signal s= o that the comparator can see the input. This will enable translation to an interrupt or an external 5V pulse you can work with Steve -----Original Message----- From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of yamanoor sairam Sent: 03 January 2014 22:22 To: Microcontroller discussion list - Public. Subject: [EE]: Garage door sensor signal interpretation I had posted a message earlier on the same topic but it did not get posted. I am assuming it is due to the large file attachments. I thought I'll repos= t my question with a smaller file size + I have more information to add to my question I am trying to use this=A0garage door sensor=A0in one of my projects. I am trying to use the sensor to detect if a person tripped the sensor. There is really no documentation for the sensor except for the=A0patent information. The sensor outputs a square wave as shown in this link: http://imgur.com/sgJfBDL The sensor outputs this signal on the 12V power line and the amplitude of the pulse is really small. (~20mV). There is no pulse when the beam is interrupted. The sensor output is also really noisy as seen in the oscilloscope capture. How do I read this square wave using a microcontroller/opamp combination to determine if the beam was interrupted. I captured this pulse on the scope by turning on the AC coupling.=A0 Sai On Friday, January 3, 2014 11:43 AM, yamanoor sairam wrote: =A0Hi, I am trying to use this=A0garage door sensor=A0in one of my projects. I am trying to use the sensor to detect if a person tripped the sensor. There is really no documentation for the sensor except for the=A0patent information. The sensor has two terminals '+' and '-'. I was able to read the data from the '+' line. The sensor is powered by a 12V source and the response is sor= t of AC in nature. I switched to AC coupling and I was able to capture the oscilloscope output.=A0 I want to interpret this signal using a comparator/microcontroller combination. In the actual system the sensor and the microcontroller would be separated by some distance (~ 3-4 feet).=A0 I tried using a precision peak detector as shown in the attached picture bu= t the voltage seems to be of a few mV. How do I convert these blips of 1V magnitude into a 5V signal so that I could count pulses using a microcontroller? When the beam is not interrupted, the blips appear as expected while the blips disappear when the beam is interrupted.=A0 Sai -- http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/chang= e your membership options at http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .