---
myst:
  html_meta:
    description: "Supported hardware for openbricks: ESP32-S3 and ESP32 boards, ST-3032/ST-3215 serial bus servos, DC gear motors, IMUs, color and distance sensors, with wiring guides."
---

# Hardware guide

A starter parts list and wiring notes. Everything here is commodity stuff you
can buy on AliExpress / Amazon / Adafruit.

## Recommended starter robot

| Part | Qty | Notes |
|------|----:|-------|
| ESP32-S3 DevKitC-1 | 1 | Any ESP32-S3 board with ≥10 free GPIOs works; classic ESP32 also supported |
| Feetech STS3032 serial bus servo (12V) | 2 | Drive wheels, continuous-rotation wheel mode. 10 kg·cm, 148 RPM no-load — datasheet in `docs/datasheets/` |
| URT-2 serial bus adapter | 1 | One half-duplex bus daisy-chains every servo |
| 3S LiPo battery (11.1V nominal) + balance charger | 1 | Feeds the servo rail directly. ST-3032 brown-out floor is ~9V, so a sagging 2S (7.4V) is not enough |
| Buck converter (12V → 5V, ≥1A) | 1 | Powers the ESP32-S3 and sensors |
| TCS34725 breakout | 2–4 | Colour sensor array for line following / zone detection |
| TCA9548A I2C multiplexer breakout | 1 | Required for more than one TCS34725 — its address is fixed at `0x29` |
| BNO055 breakout | 1 | Adafruit, Adafruit-compatible, or BNO085 with driver changes |
| ST-3215 serial bus servo | 0–4 | Optional; good for arms / grippers. Same bus and protocol, but do **not** share a 6V rail setup — see servo notes |
| Jumper wires, M3 standoffs, chassis plate | — | Your robot, your build |

A DC-gear-motor build (JGB37-520 / MG370 + H-bridge) is still fully
supported — see [Alternative: DC gear motors with encoders](#alternative-dc-gear-motors-with-encoders)
at the bottom.

## Power budget

Two rails, one battery:

```
    [ 3S LiPo 11.1V ]
        │
        ├─────────────►  URT-2 servo rail   (all ST-3032 / ST-3215 power)
        │
        └──► Buck  ──►  5V rail
                         │
                         ├──►  ESP32-S3 VIN (5V pin)
                         └──►  Sensors via 3.3V regulator on the board
```

- Never power the servos from the ESP32's 5V pin or USB — a single
  ST-3032 stall pulls more than a dev board can source.
- The ST-3032's brown-out floor is ~9V. A 3S pack sags to ~9.9V near
  empty, which still clears it; a 2S pack does not.
- Tie all grounds together: battery, buck, URT-2, ESP32, sensor
  breakouts. This sounds obvious but it's the #1 reason new builds
  misbehave.

## GPIO map (ESP32-S3)

The serial-bus build needs very few pins — that's most of its charm:

| Function          | GPIO(s) | Devices on this line |
|-------------------|---------|----------------------|
| I2C0 (SDA, SCL)   | 15, 16  | TCA9548A mux (0x70) + colour sensors behind it, IMU (BNO055, 0x28), shared bus |
| UART1 (TX, RX)    | 14, 6   | URT-2 serial bus — every ST-3032 / ST-3215 daisy-chained |
| WS2812 data       | 21      | Addressable RGB LED strip / ×8 stick DIN ({mod}`openbricks.drivers.ws2812`) — on boards that break out the header corner next to 5 V/GND, this is the free pin beside the reserved 19/20 USB pair |

Pin gotchas on the ESP32-S3:

- **GPIO 22–25 don't exist** — the pin list is 0–21 then 26–48.
- **GPIO 26–32 (and 33–37 on octal-PSRAM modules) are flash/PSRAM.**
  Do not use them.
- **GPIO 19/20 are the native-USB D-/D+** and **0/3/45/46 are
  strapping pins.**
- I2C and UART route through the GPIO matrix, so none of these
  assignments are fixed — they're the convention the bundled examples
  use. On a **classic ESP32**, the usual equivalents are I2C on
  21/22 and any two free pins for the UART.

The firmware enforces the hard cases at construction time: a driver
asked to wire a nonexistent, flash, or USB pin — or a pin the runtime
already owns, like the program button — raises
{class}`openbricks.pins.ReservedPinError` naming the pin, the role,
and the reason, instead of failing somewhere far from the mistake.
See {mod}`openbricks.pins`.

### If the status LED never lights

The onboard WS2812 speaks a write-only protocol — the firmware can't
tell a dead LED from a working one, so a blown pixel looks like
software silently failing. Run `examples/led_probe.py` on the hub: it
drives full white at both timings across every plausible RGB pin
(48/38/47/21) plus a raw `machine.bitstream` write. If nothing lights
through all of that, the problem is physical. The decisive check is a
**power-off ohmmeter reading from the LED's data pin (or its GPIO) to
GND**: a WS2812 whose DI input has failed as an internal short reads
~0 Ω there and clamps the GPIO — the pin measures millivolts even
when driven high, every write "succeeds" into the short, and the
symptom history is "worked once, then went dark for good". Lift the
data link to free the pin. Also check the schematic for **population
options in the LED circuit**. The ESP32-S3-COREBOARD V1.4
(`docs/datasheets/esp32s3_coreboard_v1.4_schematic.pdf`) routes
GPIO 48 to the WS2812 through a 0 Ω `RGB` link and feeds the LED's
VDD from the **5 V rail** through a second optional link — if either
link is unpopulated (or the board is powered via 3.3 V only, leaving
the 5 V rail dead), the LED never lights while every write succeeds.
Bridge the link / feed 5 V, or wire any external WS2812 to
3.3V / GND / GPIO 48 — it becomes the status LED with no firmware
change.

## Sensor wiring (I2C)

The baseline build has **several colour sensors** (a line-follower /
zone-detection array) plus one IMU. The TCS34725's address is fixed at
`0x29` — no address-select pins — so two of them collide on a bare
bus. The TCA9548A multiplexer solves this: it sits at `0x70` and fans
the bus out to eight isolated channels, one colour sensor per channel.
The IMU has its own address (`0x28`) and connects straight to the bus.

Wire the mux to the ESP32-S3, then each sensor to a mux channel:

| TCA9548A pin | Connect to | Notes |
|--------------|------------|-------|
| VIN          | 3.3V       | |
| GND          | GND        | Common ground with everything else |
| SDA / SCL    | GPIO 15 / 16 | The main bus — shared with the BNO055 |
| SD0/SC0 … SD7/SC7 | one TCS34725 each | Isolated channels; every sensor sits at its own `0x29` |

| TCS34725 / BNO055 pin | Connect to | Notes |
|--------------|------------|-------|
| VIN (or VCC) | 3.3V       | The breakouts have onboard regulators, but the board's 3.3V is cleanest |
| GND          | GND        | |
| SDA / SCL    | mux channel `SDn`/`SCn` (colour sensors); GPIO 15/16 directly (IMU) | |

The Adafruit breakouts include ~10 kΩ SDA/SCL pull-ups, so for a
handful of devices you don't need to add your own. In code,
`mux[n]` behaves like an I2C bus, so the sensor driver is constructed
exactly as it would be on a bare bus:

```python
from machine import I2C, Pin
from openbricks.drivers.tca9548a import TCA9548A
from openbricks.drivers.tcs34725 import TCS34725
from openbricks.drivers.bno055 import BNO055

i2c = I2C(0, sda=Pin(15), scl=Pin(16), freq=400_000)   # ESP32-S3
mux = TCA9548A(i2c)                                    # 0x70 by default
sensors = [TCS34725(mux[ch]) for ch in range(3)]       # left, mid, right
imu = BNO055(i2c)                                      # 0x28, straight on the bus
```

For a complete program — a 2-sensor array that combines each sensor's
``ambient()`` and ``rgb()`` readings to name the colour under it
(red / blue / green / yellow / white / black) — see
`examples/color_array.py`.

Simplifications when you need fewer parts:

- **One colour sensor**: skip the mux entirely; wire the TCS34725 and
  BNO055 both to GPIO 15/16 (`0x29` and `0x28` coexist fine).
- **Exactly two colour sensors**: the ESP32's second hardware I2C
  controller also works (`I2C(1, sda=..., scl=...)` on any two free
  pins), one sensor per bus — no mux.

### TCS34725 LED pin

The colour sensor breakout has two extra pins beyond power and I2C:

- **LED** — drives the onboard white illumination LED. On Adafruit
  boards it defaults **on** (tied to VIN through the ADC-enable trace).
  To control it, wire it to a spare GPIO and drive high/low; to force it
  **off**, tie LED to GND. Leave it on for consistent colour readings —
  ambient light alone is unreliable across environments.
- **INT** — the interrupt output. The driver polls, so leave INT
  **unconnected**.

## Serial bus servo notes (ST-3032 / ST-3215)

- **Every servo needs a unique bus ID.** Factory default is 1; re-ID
  one servo at a time with `examples/st3215_reid.py` (same protocol —
  it works for the ST-3032 too). The bundled drivebase examples assume
  left = 1, right = 2.
- **Speed limits.** Per the STS3032 datasheet (`docs/datasheets/`),
  no-load top speed at 12V is 148 RPM = 888 °/s; under the rated
  3.3 kg·cm load it drops to roughly ⅔ of that. The driver's default
  `max_dps=600` clamps requests at the loaded operating point —
  construct with an explicit `max_dps=900` to chase the no-load number.
- **Mixed fleets:** the ST-3215 tolerates lower voltages, but the
  ST-3032 browns out below ~9V. If you daisy-chain both on one URT-2,
  the rail must satisfy the strictest member: 12V.
- **Drivebase:** `ST3032Motor` drops straight into `DriveBase`:

```python
from openbricks.drivers.st3032 import ST3032Motor
from openbricks.robotics import DriveBase

left  = ST3032Motor(servo_id=1, uart_id=1, tx=14, rx=6)
right = ST3032Motor(servo_id=2, uart_id=1, tx=14, rx=6, invert=True)
db = DriveBase(left, right, wheel_diameter_mm=65, axle_track_mm=120)
```

Bench-test a fresh build with `examples/st3032_drivebase_test.py`.

## Calibrating the drivebase

`wheel_diameter_mm` and `axle_track_mm` are the two physical parameters that
matter for straight-line distance and turn accuracy. Measure them with
calipers or a ruler (wheel contact patch to wheel contact patch for axle
track, not hub to hub). If `straight(1000)` undershoots, your wheel
diameter value is too large; if `turn(360)` overshoots, your axle track is
too small.

High-torque 12V servos also deliver the default launch profile much more
stiffly than small DC motors — if the chassis pitches or lifts its rear
when a move starts, soften the ramp:

```python
db.settings(acceleration=180)   # wheel-deg/s²; default 1500
```

## Alternative: DC gear motors with encoders

The original starter build — still fully supported. (Both this and
the serial-servo build run in the MuJoCo simulator via the driver
shim.)

| Part | Qty | Notes |
|------|----:|-------|
| JGB37-520 DC motor with encoder (1:30 gearing) | 2 | Pick the 12V version; runs fine off 7.4V 2S LiPo |
| L298N dual H-bridge module | 1 | Cheap and robust. TB6612FNG is a better choice if you can find it |
| 2S LiPo (7.4V) + buck converter (→5V, ≥2A) | 1 each | Don't power the ESP32 from the L298N's onboard 78M05 regulator — it's good for ~300 mA and browns out the moment the motors draw current |

Wiring topology:

```
    [ 2S LiPo 7.4V ]
        │
        ├─────────────►  L298N  Vmotor   (motor power)
        │
        └──► Buck  ──►  5V rail
                         │
                         ├──►  ESP32 VIN
                         ├──►  L298N  +5V (logic only)
                         └──►  Sensors via 3.3V regulator on ESP32
```

GPIO map (see `examples/esp32_drivebase.py` for the ESP32-S3 pin
assignments; the classic-ESP32 equivalents are in git history):

| Function          | ESP32-S3 GPIO(s) | Devices on this line |
|-------------------|------------------|----------------------|
| Left motor dir    | 1, 2             | L298N / TB6612 IN1, IN2 |
| Left motor PWM    | 17               | L298N / TB6612 ENA |
| Left encoder A, B | 7, 8             | JGB37-520 encoder channels |
| Right motor dir   | 9, 10            | L298N / TB6612 IN3, IN4 |
| Right motor PWM   | 11               | L298N / TB6612 ENB |
| Right encoder A, B| 12, 13           | JGB37-520 encoder channels |

The map deliberately leaves GPIO **4 and 5** free — those are the
firmware's default **program button** and **BLE-toggle button** (see
{class}`openbricks.hub.ESP32S3DevkitHub`). The launcher polls GPIO 4
as an input, so a motor driver toggling it would read as button
presses and stop your program. GPIO 15/16 (I2C) and 14/6 (serial-bus
UART) are also kept free so sensors and a serial-servo arm can join
the same build unchanged.

### Calibrating encoder counts

The default in `jgb37_520.py` is `counts_per_output_rev=1320`, which is
`11 CPR × 30:1 × 4 (quadrature edges)`. If you have a different gearbox
variant, recompute:

    counts_per_output_rev = encoder_CPR × gear_ratio × 4

Or measure empirically: rotate the output shaft by hand exactly one full
turn and read `motor.angle()`. Whatever it reports is what
`counts_per_output_rev` should be, scaled so that one turn = 360°.
