Pi Pico Controller

This page is the shared reference point for the organiser-built Pi Pico controller, its pinout, and the first pass of nRF24L01+ bring-up. The source hardware files live in the public hack-a-bot-controller repository.

Official References

What This Page Covers

  • the current controller hardware layout
  • the real Pico pin map from the KiCad schematic
  • nRF24L01+ pin numbers and wiring on this board
  • power, test point, and input details that matter during bring-up

Controller Hardware

Schematic for the Hack-A-Bot Pi Pico controller
Full schematic export from KiCad. Open the SVG for a zoomable view of the nets and annotations.
Top-side 3D render of the Hack-A-Bot Pi Pico controller PCB
Top-side 3D board render from KiCad. Open the flat PCB plot if you want a zoomable 2D placement view.

Board Summary

From the controller schematic and board files:

  • power is designed around a 3xAA battery pack into VSYS, with the toggle switch in the battery path
  • the Pico 3V3 rail powers the radio, OLED, joysticks, and buttons
  • there are 3 joystick axes on this revision: Left_H, Left_V, and Right_H
  • the right joystick vertical axis is not routed on this board revision
  • the radio uses Pico SPI0 signals on GPIO4, GPIO6, and GPIO7, with CSN and CE on separate GPIOs
  • the OLED is wired over I2C on GPIO20 and GPIO21
  • battery voltage can be estimated in firmware using the Pico’s internal ADC3 VSYS/3 path
  • the nRF24L01+ IRQ pin is not routed to the Pico on this revision

Controller Pinout

These are the current signal assignments from the KiCad netlist:

Pico Pad Pico Function Controller Signal What It Does
5 GPIO3 STATUS status LED drive
6 GPIO4 NRF_MISO radio SPI MISO
9 GPIO6 NRF_SCK radio SPI clock
10 GPIO7 NRF_MOSI radio SPI MOSI
14 GPIO10 SW2 push button input
15 GPIO11 SW1 push button input
16 GPIO12 Left_SW left joystick select button
19 GPIO14 NRF_CS radio chip select
22 GPIO17 NRF_CE radio chip enable
24 GPIO18 Right_SW right joystick select button
26 GPIO20 OLED_SDA OLED I2C data
27 GPIO21 OLED_SCL OLED I2C clock
31 GPIO26_ADC0 Left_H left joystick horizontal axis
32 GPIO27_ADC1 Left_V left joystick vertical axis
34 GPIO28_ADC2 Right_H right joystick horizontal axis
36 3V3 +3V3 logic and peripheral supply rail
39 VSYS VBAT switched 3xAA battery input

Unused or not-routed highlights on this revision:

  • GPIO0, GPIO1, GPIO2, GPIO5, GPIO8, GPIO9, GPIO13, GPIO15, GPIO16, GPIO19, and GPIO22 are not assigned to controller features
  • GPIO28_ADC2 is the only routed axis on the right joystick
  • the Pico RUN, VBUS, ADC_VREF, and AGND pins are not used for controller features
  • the radio IRQ output is left unconnected

nRF24L01+ Bring-up

The official Nordic specification is useful for first principles:

  • supply range: 1.9V to 3.6V
  • host interface: 4-wire SPI
  • maximum SPI clock: 10Mbps
  • air data rates: 250kbps, 1Mbps, and 2Mbps
  • IRQ is active low

On this controller, the radio mapping is:

Radio Pin Module Signal Pico Connection Note
1 GND Pico GND common ground
2 VCC Pico 3V3 pad 36 3.3V only
3 CE GPIO17 on pad 22 RX/TX enable
4 CSN GPIO14 on pad 19 SPI chip select
5 SCK GPIO6 on pad 9 SPI0 clock
6 MOSI GPIO7 on pad 10 SPI0 TX
7 MISO GPIO4 on pad 6 SPI0 RX
8 IRQ not connected optional in software, unused here

GPIO4, GPIO6, and GPIO7 line up with SPI0 receive, clock, and transmit functions, so use spi0 in firmware and drive CSN and CE as ordinary GPIO pins.

Radio Pin Roles

Pin What It Does
VCC 3.3V radio supply
GND common ground
CE chip enable, used to activate RX or TX mode
CSN SPI chip select
SCK SPI clock
MOSI SPI data from Pico to radio
MISO SPI data from radio to Pico
IRQ interrupt output, active low

When you wire the radio:

  • keep the radio on a stable 3.3V supply
  • make sure the controller and Pico share a common ground
  • keep wiring short and tidy
  • remember this board has a fitted 10uF decoupling capacitor at the radio rail and an additional 100nF footprint reserved alongside it
  • test one clean transmit or receive example before you add extra features

Buttons, Joysticks, and OLED

  • SW1 is on GPIO11 and SW2 is on GPIO10
  • Left_SW is on GPIO12 and Right_SW is on GPIO18
  • because the push buttons and joystick select lines are tied up to 3V3 when pressed, configure those GPIOs with pull-downs in firmware so they do not float when idle
  • the OLED uses GPIO20 for SDA and GPIO21 for SCL
  • the routed analog joystick channels are GPIO26_ADC0, GPIO27_ADC1, and GPIO28_ADC2

Test Points

The controller also brings a few useful nets out to labelled test pads:

Test Point Signal
TP1 Left_H
TP2 Left_V
TP3 Right_H
TP4 OLED_SDA
TP5 OLED_SCL
TP6 VBAT
TP7 +3V3
TP8 GND

Bring-up Checklist

  1. Confirm the Pico builds and flashes from VS Code.
  2. Configure pull-downs on SW1, SW2, Left_SW, and Right_SW, then confirm the digital inputs switch cleanly.
  3. Read Left_H, Left_V, and Right_H on ADC0, ADC1, and ADC2, and add a calibration deadzone before you trust the joysticks.
  4. Confirm the OLED comes up on GPIO20 and GPIO21, usually at I2C address 0x3C.
  5. Bring up the radio on spi0 with MISO=GPIO4, SCK=GPIO6, MOSI=GPIO7, CSN=GPIO14, and CE=GPIO17.
  6. Prove a simple send or receive test before you start controlling motors or mechanisms.
  7. If you need battery telemetry, read the Pico’s internal ADC3 VSYS/3 path and calibrate it against a meter.

Common Failure Points

  • unstable 3.3V power to the radio
  • mixed-up chip-select or IRQ wiring
  • forgetting common ground between modules
  • forgetting to enable pull-downs on the button inputs, which leaves them floating
  • assuming the right joystick has two analog axes on this revision when only Right_H is routed
  • trying to debug radio, OLED, and input logic all at the same time

More Help

If the controller-specific mapping is still unclear after checking the schematic and repo, ask a supervisor.

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