Frequency-encoded IR sensors

A project log for Bucky Glow

A geometric object that lights up and plays music

Jonathan BumsteadJonathan Bumstead 09/23/2018 at 20:020 Comments

As a final attempt for IR sensors in the Bucky Glow, I designed frequency encoded sensors. The idea is that the IR emitter blinks at a specific frequency and the detector has a bandpass filter centered around that frequency. This way the detector is only sensitive to the IR radiation emitted from the sensor, not the surrounding IR radiation (unless by chance there is IR radiation emitted at the bandpass frequency). 

Shown below is a block design for the oscillator and bandpass filter. The signal driving the IR emitter is from a Wien bridge oscillator circuit at 1.2kHz. 

All op amps in the circuit operate at 0 to 5V because I want the board to all run on the same supply. After the photodetector is a simple bandpass filter centered around 1.2kHz. The signal is then rectified because the goal is to have a HIGH signal what the detector is blocked and LOW when it is not blocked. Without rectifying and smoothing the signal after the bandpass filter, then the output would be oscillatory.

These circuits are working pretty well, but there are again a few issues. First, this design doesn't help with the IR radiation being attenuated by the plexiglass. Second, these circuits will take a lot of time to solder, and I need one for each sensor. For these reasons, I have been moving to a mechanical pentagon switch for the Bucky Glow.