What type of electronic circuit could you use to listen to light? This page shows you some examples.
A great variety of circuits have been developed to convert light into sound, beginning with Alexander Graham Bell’s success with the photophone in 1880. This was a device that allowed wireless voice communications to be carried by a beam of sunlight. This web page is not intended to be an exhaustive historical review, rather it focuses on the Lite2Sound brand of photodiode amplifiers which are made specifically for people involved in creative audio and DIY electronics. For more historical information on the subject, we invite you to check out the links on our Resources page.
Lite2Sound™ photodiode amplifier DIY kits were first offered through ericarcher.net in 2008. Here’s how the original Lite2Sound (v2.1) looked:
This model was powered by a 3V lithium coin cell, and featured a photodiode on the tip of a flexible gooseneck arm. The circuit had a simple tone control, and a 1/4″ audio line output, but lacked a headphone jack or an automatic gain control. The schematic for Eric Archer’s Lite2Sound v2.1 is shown below:
Lite2Sound PX
In 2012, Lite2Sound PX was introduced. It was originally designed as a group workshop project for the Piksel [X] festival in Bergen, Norway.
The Lite2Sound PX photodiode amplifier’s features are designed to be just right for field recording and exploration. Its very simple to use, with just a volume control slider for the headphones. An automatic gain circuit (AGC) is built into the transimpedance amplifier that serves as its preamp. This allows it to automatically adjust for variations in the ambient light level. Simple transimpedance amplifiers tend to overload and go silent when the light gets too bright. But with Lite2Sound PX, that problem was eliminated and it is possible to listen directly to the sun! (What would you hear if you listen to the sun with a photodiode amplifier?)
Here’s the circuit for Lite2Sound PX v1.5:
Soon after its introduction, this DIY kit received a favorable review from the Noise Jockey Blog: link
Lite2Sound BC
In collaboration with Boldport Club, a special DIY kit version of the Lite2Sound photodiode amplifier was offered in 2018: link. This is a no-frills incarnation without auto gain control, but its still capable of capturing plenty of interesting sounds. In addition, it has a nice “Altoids tin” case, a colorful art sticker on the exterior, and a cool PCB design, courtesy of Ben Barwise.
Here’s the schematic for Lite2Sound BC. You can see it gets right to the point, with its transimpedance amplifier directly driving an LM386 audio power amplifier, which goes to the headphones jack, or an optional 8-ohm speaker.
Summary
The circuit schematics shown above illustrate the basic structure of a practical photodiode amplifier for audio listening. Essentially, it is a transimpedance amplifier with a PIN photodiode for input, and its output is AC-coupled into an audio power amplifier. The result is a very useful tool for people involved in creative audio, sound design, field recording, and even paranormal research!
The information on this website, including schematics, text, and graphics, is published under Creative Commons CC-BY-NC license. Authorization is granted for non-commercial use only, provided that attribution is given to the original author Eric Archer (Rare Waves LLC).