How to Make a Short-Range Infrared Sound Transmitter

There are many ways to transmit data and sound—some of which are more practical than others. Copper wire is, of course, a reliable and common medium for transmitting both digital and analog signals. When it comes to wireless transmission, radio waves have proven to be practical. Your car’s FM stereo relies on them, as does your smartphone’s WiFi connection. Optical transmissions are also possible, but light waves tend to become distorted by ambient light and other factors. If, however, you only need to relay sound over a short distance, you can build your own infrared sound transmitter and receiver.

This tutorial is intended to be a fun experiment more than a practical way to transmit sound. Transmissions are only reliable up to about one meter distance, the sound quality is low, and it requires that your transmitter be pointed directly at your receiver. But it’s still a cool demonstration of an unusual way to transmit sound. Infrared is very often used in remote controls, but that’s because only a very small amount of data needs to be transmitted. The remote control just needs to quickly blink the infrared LED in order to send a short code that corresponds to a command.

This infrared sound transmitter works a bit differently, as it’s completely analog. It’s actually sending sound more like an AM (Amplitude Modulation) radio. The transmitter and receiver boards are custom PCBs shaped like guitars, and they only contain the components necessary to transmit and amplify the signals. The transmitter board has a 3.5mm audio jack for input. The audio signal is fed through triode modulation to the infrared LED. That causes the light to change in amplitude with the audio signal. The receiver board then picks up that light, passes it to a small amplifier, and then pushes it out through a tiny speaker. You probably won’t want to use this technique to make wireless headphones or anything, but it does make a great science class demonstration.