This is an old revision of the document!

Updated Traffic Lights Using Transistors for Improved LED Brightness

Jul 2026

Introduction

In our first attempt at doing the Traffic Lights, we are getting our supply for the LEDs from the GPIO pins, there are two issues with doing this:
The GPIO Pins only seem to supply around 12mA. There is a way to force more, but you meed to use C++ the GPIO Voltage is only 3.3v

What we want to do is to drive the LEDs from the same 5V rail that is powering the Pico (or whatever board you are using). To turn on the LEDs (and protect the GPIO pins from over-current) we can use some Transistors. Transistors are generally associated with amplifier circuits, but you can use them as a simple switch.

See below for a diagram of what we want to achieve.