When it misbehaves
The key and the light share only GND and VCC, so they fail apart: a key that reads perfectly beside a dark LED is one fault, not two. Decide which half is wrong first, then check the wire, the pin number and the one line of code that half depends on.
Which half
Run the first press sketch and watch two things: the serial monitor, which is the key, and the keycap, which is the light.
- Lines print, the key stays dark: the light. Look at the WS2812 wire,
LED_PIN, and theshow()orwrite()call. - The key lights, but nothing prints or it prints the wrong thing: the
key. Look at the BUTTON wire,
BUTTON_PIN, and the test for HIGH. - Neither: what they share, VCC and GND.
The key
A key that never reads HIGH has no VCC, or is being read on the wrong pin: the pull-down holds BUTTON LOW until the switch joins it to VCC. A key that reads backwards is being tested for LOW, the mistake the page this handbook replaced made. A key that steps two modes for one press is bouncing, and needs the debounce the modes sketch uses.
The light
A dark LED is a missing show(), the wrong pin, or no supply. Red showing as
green is the colour order: NEO_GRB. Green and blue weak beside a bright
red, on a 3.3 V board, is the LED running under its 3.5 V minimum. It is not
broken; One VCC, two
jobs shows how to give
it 5 V without putting 5 V on your pin.
When it does not work
That is the half they share: GND and VCC. Check both wires, and that VCC is on a pin that has power. With VCC off, BUTTON stays LOW through the pull-down and the LED has no supply, which looks exactly like two faults at once.
A WS2812 can start up showing something before it is told anything. Both sketches send a dark frame in setup() for that reason. If yours does not, add key.show() (Arduino) or key.write() (MicroPython) straight after starting the LED.
Something is shorting when the key closes: most likely BUTTON is on a pin that is driving an output, or VCC and GND are swapped. Unplug it and check the four wires against the square pad before trying again.
The board has no capacitor at the LED, though its maker's sheet asks for one. Keep the wires short, and if it still flickers put 100 nF across VCC and GND at the header.
Five LEDs of the same kind in a chain on one data pin, and why that one wants 5 V on VCC.
The TK33 WS2812 RGB LED Bar →Edit this page — content/books/mechanical-key/when-it-misbehaves.mdx
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