Thursday, 24 November 2011

Multi-lights controller for toy cars

As one of the younger members of HackLlan Jason was busy making LED traffic lights for his younger brother last Thursday. This week, we've been working on taking that idea to the next level.

Instead of a simple pin-on, pin-off with delay approach, we've changed the code in the microcontroller to use a single Timer0 interrupt (raising an "event" every 1ms) and a number of counters and state machines to control lots of different devices all at the same time.

Instead of the smaller 16F628A chip (used in the original prototype) we've gone to the other end of the scale and put in a massive 40-pin 18F4550. This gives us plenty of i/o options. So far, we've kept PORTB for inputs (using the internal pull-ups to reduce the final component count), put the traffic lights on PORTD and used PORTC for the servo and LED controller for the level crossing.

The what???

That's right. This controller now simultaneously handles:

  • two sets of inter-dependent traffic lights
  • two sets of alternate flashing level crossing lights
  • two servos (level crossing gates)
  • a one-shot fire-on-release ultra-bright LED (speed camera)

There are still plenty of spare i/o pins to add more to this project in the future (pelican crossing, belisha beacon etc) but we need to think about finishing off what we've got here, otherwise it'll be Xmas and we'll still have everything on a loose-wired breadboard (which let's be honest, won't be much of a final gift!)

Here's a video showing the breadboard, controlling all the different lights and servos at the same time -
well done Jason!

Note how the traffic lights continue to work independently of the other things on the board - the alternating lights work separately to the traffic lights, and the servo signals are being sent every 20ms to update the servo horn/gate positions. And all the while the speed camera goes off at periodic intervals!