This program implements a traffic light state machine on an RP2040 microcontroller using hardware timers. The traffic light consist of a RED, YELLOW and GREEN LEDs for the car lights and a RED and GREEN LEDs for the pedestrian ligths.

This state machine mirrors the french traffic lights system.

There are four states which are automatically cycled by default. But there is a pedestrian button fo force the transition between CARS_PASS and CARS_WARNING states.

The states are cycled automatically by hardware timers. The delays can be adjusted by editing this constants in the main.c file.

const uint32_t pedestrians_delay_ms = 8000;   // Time for the Pedestrians to pass (ms)
const uint32_t warning_delay_ms = 4000;       // Amount of time the warning states are shown (ms)
const uint32_t cars_delay_ms = 16000;         // Time for the cars to pass (ms)

Here is a video showing the project in action

Binaries are available in the github actions tab.

First and foremost, clone this repository using git.

git clone https://github.com/RedBlaze42/RP2040-C-TrafficLights.git

First, install all the packages required for building C for arm:

sudo apt install cmake gcc-arm-none-eabi libnewlib-arm-none-eabi libstdc++-arm-none-eabi-newlib

Then clone the pico sdk from inside this repository directory:

cd RP2040-C-TrafficLights

git clone https://github.com/raspberrypi/pico-sdk.git

Go inside and update the submodules to add tinyusb support:

cd pico-sdk && git submodule update --init && cd ..

You have to tell cmake where to find the pico sdk, when still in the project root, you can run this command:

export PICO_SDK_PATH=`pwd`/pico-sdk

Create the build directory and go inside it:

mkdir build && cd build

Then you can configure and build the project:

cmake .. && make

The build files will be in your current directory (RP2040-C-TrafficLights/build).

For windows, a full tutorial on how to insall the Raspberry Pi Pico C/C++ SDK for is available on the official raspberry pi website.

While plugging the RP2040 to your computer, press the BOOTSEL button to program it. You can then mount the mass storage device and drop the .uf2 file. The RP2040 should reboot and start the program.

You can edit the pin configuration by editing these lines in the main.c file

// Led pins
const uint CARS_RED_PIN = 7;
const uint CARS_YELLOW_PIN = 6;
const uint CARS_GREEN_PIN = 5;
const uint PEDESTRIANS_RED_PIN = 4;
const uint PEDESTRIANS_GREEN_PIN = 28;

// Button pin
const uint PEDESTRIANS_BUTTON_PIN = 29;

The number here are refering to the GPIO pin numbers which is different from the board pin numbers.

You need to connect the other side of the pushbutton to GND because there is an internal pullup resistor activated on this pin.

Don't forget to connect resistors in series with the LEDs to protect them.

This code uses the CMake build system recommended by the Raspberry Pi Pico C/C++ SDK.

By default, the debugging is done with the UART protocol via the usb port using the tinyusb submodule, but you can switch to the GPIO UART by changing these lines in the CMakeLists.txt file:

# Enable usb output, disable uart output
pico_enable_stdio_usb(${PROJECT_NAME} 1)
pico_enable_stdio_uart(${PROJECT_NAME} 0)

by

# Disable usb output, enable uart output
pico_enable_stdio_usb(${PROJECT_NAME} 0)
pico_enable_stdio_uart(${PROJECT_NAME} 1)

A python testbench is available in the tests directory. It uses the USB/UART communication to check if the state transitions are correct and made at the right time.

You need to install Python 3 from the official website. Or using apt: sudo apt install python3 python3-pip python3-venv

From inside the tests directory, create a virtual environment using python -m venv rp2040_trafficlights_tb.

Activate it with source rp2040_trafficlights_tb/bin/activate on Linux or rp2040_trafficlights_tb\Scripts\bin\activate on Windows.

Install the pyserial package by running the command python -m pip install -r requirements.txt from inside the tests directory.

Compile the project with the DEBUG macro, launch the testbench using python device_test.py. By default, the testbench will run for 5 minutes.

This is the expected output:

Switched from TrafficState.PEDESTRIANS_WARNING to TrafficState.CARS_PASS after 4000 ms with an error of 0 ms
WARNING: Negative delay error of -9280 ms for CARS_PASS -> CARS_WARNING, it's normal if you have pressed the pedestrian button, otherwise it's an error.
Switched from TrafficState.CARS_WARNING to TrafficState.PEDESTRIANS_PASS after 4000 ms with an error of 0 ms
Switched from TrafficState.PEDESTRIANS_PASS to TrafficState.PEDESTRIANS_WARNING after 8000 ms with an error of 0 ms
Switched from TrafficState.PEDESTRIANS_WARNING to TrafficState.CARS_PASS after 4000 ms with an error of 0 ms
Switched from TrafficState.CARS_PASS to TrafficState.CARS_WARNING after 15999 ms with an error of -1 ms
Switched from TrafficState.CARS_WARNING to TrafficState.PEDESTRIANS_PASS after 4000 ms with an error of 0 ms
Switched from TrafficState.PEDESTRIANS_PASS to TrafficState.PEDESTRIANS_WARNING after 8000 ms with an error of 0 ms
Switched from TrafficState.PEDESTRIANS_WARNING to TrafficState.CARS_PASS after 4000 ms with an error of 0 ms
Switched from TrafficState.CARS_PASS to TrafficState.CARS_WARNING after 16000 ms with an error of 0 ms
...
Switched from TrafficState.PEDESTRIANS_WARNING to TrafficState.CARS_PASS after 4000 ms with an error of 0 ms
Switched from TrafficState.CARS_PASS to TrafficState.CARS_WARNING after 15999 ms with an error of -1 ms
Test passed without any errors

As you can see, I pressed the pedestrian button at the start of the test.

And this is when an error occurred:

Switched from TrafficState.PEDESTRIANS_WARNING to TrafficState.CARS_PASS after 4000 ms with an error of 0 ms
WARNING: Negative delay error of -14768 ms for CARS_PASS -> CARS_WARNING, it's normal if you have pressed the pedestrian button, otherwise it's an error.
Switched from TrafficState.CARS_WARNING to TrafficState.PEDESTRIANS_PASS after 4000 ms with an error of 0 ms
Switched from TrafficState.PEDESTRIANS_PASS to TrafficState.PEDESTRIANS_WARNING after 8000 ms with an error of 0 ms
Traceback (most recent call last):
  File "c:\Users\Hugo\OneDrive\Projet ASL\tests\device_test.py", line 61, in <module>       
    raise Exception(f"Illegal switch from {device_state} to {incoming_state}")
Exception: Illegal switch from TrafficState.PEDESTRIANS_WARNING to TrafficState.CARS_WARNING