Wireless audio over free-space infrared optical link
free-space optics · IR · analog electronics · audio
- problem
- Optical communication usually means fibre; free-space links are for where wires can’t go — and a narrow beam is much harder to intercept, or even detect, than RF. The goal here: the most budget-friendly working demonstration possible — send music across a desk on a beam of light.
- approach
- An Arduino plays a two-second 8-bit mono loop (a custom Python pipeline resamples any track until it fills 99% of memory) through a TLC7524 DAC and an LM358 buffer pair, modulating an IR LED’s intensity. On the receive side, an IR phototransistor feeds a trimpot divider — keeping the LM386 under its 0.4 V input ceiling — and a gain-of-50 amplifier drives the speaker. Transmit and receive run on separate supplies, after a shared rail audibly coupled the song into the power lines.
- result
- Roughly 80% clear audio across more than a metre of open air — up from the ~6 cm the visible-light prototypes managed — with oscilloscope traces confirming the speaker output tracks the source signal closely.
- lessons
- Ambient light is the loudest thing in the room: switching from visible light to IR bought more range than any circuit change. Alignment and narrow component operating windows set the real limits — the next revision moves to PCBs, 3D-printed alignment guides, and proper light shielding.
![[PLACEHOLDER: photo of the IR transmitter and receiver pair on the bench]](/images/projects/ir-audio-link.svg)
![[PLACEHOLDER: photo of the assembled gimbal holding the camera]](/images/projects/gimbal-camera.svg)