jessikitty
c21f804812
Keeps the shared-rail version documented as the alternative, since that is what the current loom attempts, and links the new pinout reference.
89 lines
3.2 KiB
Markdown
89 lines
3.2 KiB
Markdown
# Wiring
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Pin availability and limits: [ESP32-PINOUT.md](ESP32-PINOUT.md).
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## Board to board
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| Board A (esp32_bluepad32) | | Board B (esp32 2.0.17) |
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| --- | --- | --- |
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| GPIO17 TX | → | GPIO16 RX |
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| GPIO16 RX | ← | GPIO17 TX |
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| GND | — | GND |
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| 5V | — | 5V (model setup only, see README) |
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TX goes to RX, not TX to TX. The ground is a shared voltage reference so the
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two boards agree on what a logic 1 is — without it you get garbage or silence.
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It is not a return path for anything else, so do not hang LED current off it.
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## LED circuits — recommended build
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Each LED gets its own wire out and its own wire back to its own GND pin. Four
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wires, no shared junction anywhere.
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```
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GPIO25 ──[220Ω]──▶|── RED pair ──── GND (a)
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GPIO26 ──[100Ω]──▶|── GREEN pair ── GND (b)
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```
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GND (a) and GND (b) are different physical pins but the same net inside the
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board. That is fine, and it is exactly what makes this safe: there is no shared
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connection point to wire incorrectly.
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Both circuits live entirely on **board B**. LED long leg (anode) faces the
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resistor and GPIO side. A reversed LED simply stays dark, so it looks like a
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dead circuit rather than a wiring error.
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Resistor values are a starting point: roughly 220Ω for red, 100Ω for blue or
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white. A pin is comfortable at about 12mA and hard-limited near 40mA. If a pair
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draws more than ~20mA — which pre-wired "3V" LEDs sized for a coin cell often
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do — drive it through a small NPN transistor or MOSFET instead of off the pin.
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## Shared ground rail — the other way
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Also valid, one wire fewer, but it has a junction that can be wired wrong:
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```
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GPIO25 ──[220Ω]──▶|── RED pair ────┐
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├── ground rail ── board B GND
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GPIO26 ──[100Ω]──▶|── GREEN pair ──┘
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```
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The two returns must meet **only at the ground rail**, and the rail goes
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straight to a GND pin. See the failure mode below for what happens when that
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junction lands in the wrong place.
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## Known failure mode: LEDs wired in series
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Symptom seen on this build — green only lights when red is already on, and
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green never lights alone:
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| Software state | Observed |
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| --- | --- |
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| red on, green off | red on ✓ |
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| red off, green on | **both off** ✗ |
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| red on, green on | both on ✓ |
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| red off, green off | both off ✓ |
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Cause: the green return lands on the *anode* side of the red LED rather than on
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the ground rail, putting the two LEDs in series. Green alone then has to push
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through both — roughly 2.1V plus 1.9V — and a 3.3V pin cannot do it, so neither
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lights. With GPIO25 also high, the junction is lifted and both conduct.
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Two rows of that table are impossible from a software fault, which is what
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identifies it as wiring.
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**Test:** with both LEDs off, meter from the shared return wire to a GND pin.
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It must read 0V. Press Circle and measure again — if it rises above 0V, that
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wire is not ground.
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**Fix:** switch to the separate-ground build above. It removes the junction
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entirely, so this cannot recur.
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---
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Created by: Jess Rogerson (yelling commands at Claude.AI)
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