Test and Adjustment of IR Sensor System
Educational Revision
BEST Robotics Inc © 2019
Page
4
Step 3: Adjust the System’s Sensitivity
For help in debugging, the transmitter board has a red LED that will be on when the IR emitter is
on. The receiver board has a red LED that will be on when an IR signal is detected. Due to the limited
power available, the receiver LED is fairly dim.
The IR signal is modulated at 38KHz to reduce sensitivity to other light sources – the detector is
tuned to 38KHz and is less sensitive to constant light or other modulation frequencies. For maximum
sensitivity tune the transmitter board to 38KHz. You can adjust the modulation frequency to adjust the
system’s sensitivity by turning the white potentiometer on the transmitter board. There are a couple
ways to make this adjustment.
If you have an oscilloscope or frequency counter connect it to pin 7 of the 8-pin DIP to monitor
the frequency. If you lack that equipment, don’t panic. You can do a pretty good job without any
special test equipment. Separate the transmitter and receiver until the receiver just barely detects the
IR signal. Now when you adjust the potentiometer you should find that the receiver detects the IR
signal somewhere in the middle of its range of travel but does not detect the IR signal at either the
counter-clockwise extreme or the clockwise extreme. Find the two spots of the potentiometer’s travel
where it switches between detecting and not detecting and set the potentiometer halfway between
these two points.
You may not want maximum sensitivity. Perhaps your transmitter and receiver are very close
together, counting wheel spokes as they go past, for example. Frustratingly, it doesn’t work reliably
because the receiver is also picking up reflections from other parts of your robot. In this case you can
“detune” the transmitter so that your receiver can detect the strong signal from the transmitter but not
the weaker reflections. Flat black paint may also be your friend here.
