jessikitty
069e7ebdd5
Records the diagnosis: green only lights when red is on, because the green return reaches the red LED's anode instead of the ground rail.
2.6 KiB
Wiring
Board to board
| Board A (esp32_bluepad32) | Board B (esp32 2.0.17) | |
|---|---|---|
| GPIO17 TX | → | GPIO16 RX |
| GPIO16 RX | ← | GPIO17 TX |
| GND | — | GND |
| 5V | — | 5V (model setup only, see README) |
TX goes to RX, not TX to TX. The ground is a shared voltage reference so the two boards agree on what a logic 1 is — without it you get garbage or silence. It is not a return path for anything else, so do not hang LED current off it.
LED circuits
Both live entirely on board B. Each is its own complete loop:
GPIO25 ──[220Ω]──▶|── RED pair ────┐
├── ground rail ── board B GND
GPIO26 ──[100Ω]──▶|── GREEN pair ──┘
The two returns meet only at the ground rail, and the rail goes straight to a GND pin on board B. LED long leg (anode) faces the resistor and GPIO side.
Resistor values are a starting point: roughly 220Ω for red, 100Ω for blue or white. A pin is comfortable at about 12mA and hard-limited near 40mA. If a pair draws more than ~20mA — which pre-wired "3V" LEDs sized for a coin cell often do — drive it through a small NPN transistor or MOSFET instead of off the pin.
Known failure mode: LEDs wired in series
Symptom seen on this build — green only lights when red is already on, and green never lights alone:
| Software state | Observed |
|---|---|
| red on, green off | red on ✓ |
| red off, green on | both off ✗ |
| red on, green on | both on ✓ |
| red off, green off | both off ✓ |
Cause: the green return lands on the anode side of the red LED rather than on the ground rail, putting the two LEDs in series. Green alone then has to push through both — roughly 2.1V plus 1.9V — and a 3.3V pin cannot do it, so neither lights. With GPIO25 also high, the junction is lifted and both conduct.
Two rows of that table are impossible from a software fault, which is what identifies it as wiring.
Test: with both LEDs off, meter from the shared return wire to a GND pin. It must read 0V. Press Circle and measure again — if it rises above 0V, that wire is not ground.
Simplest fix: give each LED its own separate wire back to its own GND pin on board B, with no shared return at all. Board B has several grounds, all common internally. Slightly less tidy, and it removes the junction entirely.
Worth checking polarity at the same time. A reversed LED simply stays dark, so it looks like a dead circuit rather than a wiring error.
Created by: Jess Rogerson (yelling commands at Claude.AI)