Wemos RGB LED shield
I got a Wemos RGB shield. This is a nice little shield for the D1 Mini that has 7 RGB LEDs (WS2812B-mini). The LEDs are pretty bright with and have good color saturation.
Rewiring the IO pin
The shield is wired to use D4 as the control pin. However, this has a large downside – D4 is also the pin of the built-in LED. This means that the shield turns on immediately by default. However, at full brightness it takes some minutes to fully recover your sight if you look at the LEDs. Disabling the built-in LED during setup does not fully solve this problem, since the LED is also used during flashing.
Fortunately, Wemos has made it pretty easy to rewire the control pin:
- First use a sharp, thin knife to cut the wiring between the two pads that are marked D4.
- Pick another pin and solder the pad corresponding to that pin to the middle pad.
The pads are pretty small and can be difficult to connect. I found that putting a thick blob of tin on the tip and dropping it somewhere between the pads works well.
Picking a pin can be somewhat difficult, especially if you want to retain the possibility to use I2C or SPI. Initially I made the mistake to choose pin D0. Do not use pin D0, it does not support PWM, which is necessary for driving the LEDs. I finally settled on pin D3, which works very well.