Hardware Overview

This page provides an overview of the hardware components used on the
Pololu 3pi+ 2040 and Pololu Zumo 2040 robots.
Both platforms share the same RP2040 control board and peripheral layout.

Common Hardware (shared by both robots)

  • RP2040 microcontroller (same as Raspberry Pi Pico)
  • Differential-drive system (2 motors + 2 encoders)
  • LSM6DSO 6-axis IMU (Accel + Gyro)
  • LIS3MDL 3-axis Magnetometer
  • 5 × Line reflectance sensors (RC type)
  • 2 × Bump sensors (IR reflectance)
  • SH1106 128×64 OLED display (SPI)
  • 6 × RGB LEDs (APA102-compatible)
  • Micro SD card (requires individual deck for each robot)
  • 3 user buttons (A, B, C)
  • 1 buzzer (PWM capable)
  • USB-C connector
  • Full pinout compatibility with RPi Pico ecosystem

Pinout Diagram

Below is a high-level overview.

Component Pins Notes
Motors (PWM) GP14, GP15 PWM7 A/B
Motor direction GP10, GP11 H-bridge control
Encoders PIO inputs on GP8–GP13 Quadrature
IMU I2C SDA = GP4, SCL = GP5 Shared bus
OLED SPI GP0, GP1, GP2, GP3 SH1106
RGB LED SPI GP3 (TX), GP6 (CLK) APA102
Line sensors GP18–GP22 RC decay timing
Bump sensors GP16, GP17 IR reflectance
SD Card Deck GP18(SCK), GP19(MOSI), GP20(MOSI), GP21(CS) SPI0 (shared conflict with Line sensors)
Buzzer GP7 PWM3B
Buttons A/B/C GP25, GP1, GP0 A shares LED pin

Pin Assignment for Zumo and 3pi

Pololu 3pi+ Pin Assignment

Pololu 3pi+ Pin Assignment Pololu 3pi+ Pin Assignment

Pololu Zumo Pin Assignment

Pololu Zumo Pin Assignment Pololu Zumo Pin Assignment

Extensions and Decks

Both robots has individual decks that can be stacked on top of the base board to provide additional functionality, mainly for the nRF52840 Dongle and the micro SD card. Since both boards share the same functionality, the BOM files for both decks are provided here.

Pololu Deck

The Pololu Deck provides compatibility with the nRF52840 Dongle for wireless communication and a micro SD card slot for data logging. The deck connects to the base board via the headers on the main board. The manufacture file for the Pololu Deck can be found here.

Pololu Deck

Zumo Deck

The Zumo Deck provides compatibility with the nRF52840 Dongle for wireless communication and a micro SD card slot for data logging. The deck connects to the base board via the headers on the main board. For the current Zumo Deck a crazyflie micro sd card deck would be needed, but later it would be replaced by a single micro sd card port. The manufacture file for the Zumo Deck can be found here.

Zumo Deck

Actuators

Yellow LED

  • Connected directly to RP2040 GPIO25
  • Same pin as Button A → cannot use both simultaneously
  • Example uses: status blinking, debugging

Motors

Pins

  • Direction:
  • GP10 → Right motor direction
  • GP11 → Left motor direction
  • PWM:
  • GP14 → Right motor speed (PWM7A)
  • GP15 → Left motor speed (PWM7B)

Quadrature Encoders

  • Connected to both wheel shafts
  • Uses custom PIO program (reads rising & falling edges on phases A/B)
  • Provides:
    ✔ position (ticks)
    ✔ velocity (RPM)

Pin usage

  • Typically GP8–GP13 depending on model (RP2040 PIO banks)

IMU (LSM6DSO + LIS3MDL)

LSM6DSO — 6-axis IMU

  • Accelerometer + Gyroscope
  • I2C address: 0x6A
  • Used for orientation & angular velocity

LIS3MDL — 3-axis Magnetometer

  • I2C address: 0x1E
  • Provides heading estimation (Yaw)
  • Not used currently in indoor environment due to drifting

Bus pins

  • SDA: GP4
  • SCL: GP5
  • Both sensors share the same bus

OLED Display (SH1106)

Connection

  • SPI0:
  • Data: GP0
  • Reset: GP1
  • SCK: GP2
  • MOSI: GP3

Features

  • 128×64 pixels
  • Monochrome
  • Used for menus, data display, debugging

RGB LEDs (APA102-compatible)

  • 6 individually addressable LEDs
  • Arranged in a circular layout around the board
  • Order: A → F (counterclockwise)

Pins

  • Data (TX): GP3
  • Clock (SCK): GP6

OLED and RGB LEDs share SPI0 but use different SCK pins → no conflict.

Line Sensors (5×)

  • Positions: under robot front edge
  • RC reflectance type (similar to Pololu QTR sensors)

Pins

  • Emitter: GP26
  • Sensors:
  • DN1 → GP22
  • DN2 → GP21
  • DN3 → GP20
  • DN4 → GP19
  • DN5 → GP18

Notes

These pins conflict with SD card deck SPI pins. SD logging requires disabling line sensors.

Bump Sensors (2×)

Located near front bumper skirt.

Pins

  • BL → GP17
  • BR → GP16
  • Emitter → GP23

Used to detect collision/contact direction.

Buzzer

  • Pin: GP7
  • Supports hardware PWM mode (PWM3B)
  • Can play simple tones, beeps, or melodies

Buttons

Button Pin Notes
A GP25 conflicts with LED
B GP1 (QSPI_SS_N) special function pin
C GP0 simple GPIO

Pressing pulls the pin to GND.

SD Card Deck

Compatible with Crazyflie micro SD card deck. There are also decks specially designed for both robots that help us get rid of the cables when using the Crazyflie micro SD deck.

Pins (SPI0)

  • CLK: GP18
  • MOSI: GP19
  • MISO: GP20
  • CS: GP21

Important

  • These pins conflict with line sensors → only one can be used at a time
  • Required for trajectory logging (CSV), trajectory loading and robot configuration parameters loading.