LED Indicators Wiring
Edit on GitHubThe red and blue status LEDs: which GPIO, what resistor, and what the blink patterns mean.
LED Indicators Wiring
Two LEDs give instant visual status: red for BEACON, blue for SEARCH. This page covers the wiring and the blink language.
The circuit
| LED | GPIO | Series resistor |
|---|---|---|
| Red (BEACON) | GPIO 27 | 330 Ω to GND |
| Blue (SEARCH) | GPIO 26 | 330 Ω to GND |
Anode to GPIO through the resistor, cathode to GND. At 3.3 V a 330 Ω resistor gives about 6-8 mA, plenty bright for a 3 mm LED.
Blink patterns
| Pattern | Meaning |
|---|---|
| Red slow blink | BEACON mode, transmitting cycle |
| Blue slow blink | SEARCH mode, scanning |
| Blue fast blink | Signal detected in SEARCH |
| Red fast blink | EMERGENCY mode |
| Both blinking | CONFIG mode (WiFi AP active) |
Wiring mistakes to avoid
- Reversing anode/cathode: LED just stays dark. If both LEDs never light and the rest works, check polarity.
- Missing resistor: the LED draws too much current and can damage the GPIO. Always include the 330 Ω.
- Sharing one resistor: each LED needs its own series resistor.
- Using the input-only pins (34/35) for LEDs: they cannot drive outputs.
Testing
With the multimeter in diode mode, a good LED shows ~1.6-2.0 V forward drop in one direction and open in the other. In-circuit, verify about 2 V across the LED when lit.
If the LEDs are too bright or dim
- Too bright at night: increase the resistor to 470-680 Ω.
- Too dim: check the supply rail or reduce to 220 Ω (stay above 150 Ω for 3.3 V).
The blink timing lives in firmware; see the LED Status Indicators wiki page for the full pattern reference.