# Wiring

![Wiring pinout](wiring.svg)

## 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)