Two channel traffic lights controller — using Wemos :: Cavelab blog

My kids wanted traffic lights for their LEGO city, so first I had to build a traffic lights controller.

I haven’t gotten around to making the actual traffic lights yet — but I have made a dual channel, Wi-Fi enabled, MQTT controlled traffic lights controller. That follows the standard set by the Norwegian Public Roads Administration.

Table of contents

Sequence and timing

I’ve followed the standard set by the Norwegian Public Roads Administration, in handbook 303 and 310.

Yellow time: 3-4 seconds, depending on speed limit (above or below 50 km/h)
Red/yellow time: 1 second
Yellow and red/yellow time for two conflicting flows of traffic must not overlap
Switching time: t_switch = t_clear - t_enter
Yellow flash: 60 times per minute (1 Hz), 50% interval

Cold start

5 seconds yellow flash
5 seconds yellow solid
5 seconds red (minimum), all directions
1 second red/yellow main direction
Green main direction

The build

This was a really simple build, it’s all on a stripboard for now. I’m powering everything with the micro USB connector on the Wemos micro controller, but I have added pin-headers for a 5V external supply, with a protection diode.

So the only additional component needed, in addition to the Wemos, is a Darlinton-driver to power the actual LEDs. I added plenty of pin-headers to make it easy to connect the traffic light LEDs.