Infrared Receiver (IR Rx) Output Waveform

In the picture above, Oscium’s iMSO-104 oscilloscope is measuring the output waveform of an infrared receiver (IR Rx). The iPad and iMSO are functioning as the oscilloscope for measuring the receiver’s output signal as the relative alignment between transmitter and receiver varies. There are two waveforms captured on the oscilloscope screen. Trace 1, the Reference trace (in grey) is the full scale Rx output from a 0 degree, on axis Rx/Tx alignment. The active measurement trace (in green) is being measured as the IR transmitter is rotated off axis with the receiver. You can witness this action in this short video clip… complete with audio. Turn up your speakers!

What's Happening in Video 

The infrared transmitter and receiver are set 12-18” apart from each other on a flat, horizontal surface. When you think about signal strength for wireless devices like cell phones, radios, televisions, and satellites, you think of how the antennas on the receiver and transmitter units are aligned. For this application, however, we don’t have antennas. Instead of parabolic dishes, weird metal shapes etched in a circuit board, or telescoping wands that are mechanical structures obviously functioning as antennas, the infrared receiver and transmitter units rely on a special class of diodes for their antennas.

The figure below shows the handheld oscilloscope screen displaying the strongest and weakest signals measured at the receiver’s output without triggering the alarm. When the transmitter is perfectly aligned with the receiver, the output waveform’s peak-to-peak voltage is at its maximum value. I used the oscilloscope’s reference capture function to save the trace and preserve it for display on the screen.

As demonstrated in the video clip, I can rotate the transmitter about thirty degrees off axis from the receiver before tripping the receiver’s alarm. I’ve superimposed the arc or rotation in the picture of the setup for this “experiment” for reference. When the received signal decays to a predefined limit, a comparator voltage trips and turns on the buzzer.


Try It At Home!

A follow on experiment to what I’ve done here would be to move the two units apart horizontally, keeping them aligned, and see how far apart they can be while maintaining sufficient signal strength. The IR Rx/Tx kit used for this post is available at any Radio Shack. Click here to follow a link to the product page on Radio Shack's website. The team at Oscium would like to hear about your own experiements, so please let us know.

Oscium's handheld oscilloscope is now available with universal platform support! So, if you're interested in using the scope on iOS, Android, PC or Mac, Oscium supports you. Please go to iMSO-204x for more information.