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 repo= st 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 t= he pulse is really small. (~20mV). There is no pulse when the beam is inter= rupted. The sensor output is also really noisy as seen in the oscilloscope = capture. How do I read this square wave using a microcontroller/opamp combi= nation to determine if the beam was interrupted. I captured this pulse on t= he scope by turning on the AC coupling.=A0 Sai On Friday, January 3, 2014 11:43 AM, yamanoor sairam wrote: =20 =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 combinat= ion. In the actual system the sensor and the microcontroller would be separ= ated 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 m= agnitude into a 5V signal so that I could count pulses using a microcontrol= ler? When the beam is not interrupted, the blips appear as expected while the bl= ips disappear when the beam is interrupted.=A0 Sai --=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 .