Damien Walsh Recycles Panelized LED Boards as an ESP32-Controlled LED Matrix Display
With a set of panelized Cree LED boards, some copper tape, a series of LED matrix driver chips and an ESP32, a display is born.
Computer science graduate Damien Walsh has found a novel use for panelized LED modules: a 20x5 LED matrix, driven by a custom matrix driver and clever application of copper tape.
"I’m lucky to have friends working in the electronics industry in various different capacities. Through them, I'll occasionally get hold of some unwanted/rejected/surplus boards or components that would otherwise just end up in the WEEE bin," Walsh explains. "This time, it’s some LED boards. Each board has 100 LEDs pre-soldered to it. There’s no connection between any of the LEDs, but they are arranged into a 20-by-5 matrix."
The boards were originally designed for high-output lighting systems, and are panelized — multiple individual boards produced on a single PCB, one LED per board, and designed to be snapped out and used one-at-a-time. "I decided that at a more sensible current, the rectangular array layout of the LEDs could be leveraged to produce a display," Walsh notes. "I set to work finding a suitable driver to run the whole array as a multiplexed matrix."
After discarding a couple of possible solutions, Walsh settled on an ISSI IS32FL3738 dot-matrix LED driver IC capable of supporting up to a 6x8 matrix; by daisy-chaining multiple driver chips together, Walsh had a way of controlling the LEDs in the matrix. Coupled with an Espressif ESP32-WROOM microcontroller, Walsh had everything set up for remote control.
"The layout of the actual controller ICs was the most important aspect, and also the most challenging," Walsh writes. "Breaking out the 14 outputs while also ensuring good power & ground connectivity was tricky. I found that using the front copper layer for the current sinks and the rear copper layer for the current sources worked well. Routing the I2C communication traces on the back of the board allowed me to keep them together and also keep space around the ICs for the much-needed decoupling capacitors for these power-hungry chips."
While waiting for the control board to be produced, Walsh turned to finding a way to electrically link all the otherwise-unconnected LED modules. "I experimented with different wiring approaches," he explains, "but the best approach by far proved to involve self-adhesive copper tape applied in strips across the PCB and then solder-bridged to the required contacts. For any places where the tape strips needed to cross, I used Kapton polyimide tape to provide some insulation between the strips. This was all very fiddly at first but after a while I became quite efficient at cutting the 3mm-wide strips of copper tape and applying them accurately."
Finished with a diffuser, which sandwiches thin tracing paper between 3D printed frames, the result is a large-format yet low-resolution display board capable of wireless control and autonomous updates — and which may yet be joined by additional boards designed to operate as a single matrix.
Walsh's full write-up is available on his website. while the source code for the ESP32 controller firmware is available on his GitHub repository.