Gadget Freak

Peter Griffiths - the man who turned a lamp into a work of art - moves into pole position with the featured Gadget Freak for August.

Based around LED cluster modules and a microcontroller, the circuit drives F1-style gantry race start lights.

Who wouldn't want to be the race controller, with their finger on the starting switch?

Fully documented in terms of parts and the build process, Peter has provided loads of photos to help navigate construction. And for those of you who don't have access to PCB making facilities, there are photos of building the project on stripboard.

And note, the lights are suitably bright for indoor or outdoor use. (The brightness control input is an analogue signal varying from 0 volts (dim) to 5 volts (bright). For the technically minded it is possible to modify the circuit to use a Light Dependant Resistor to automatically adjust the LED brightness to match the ambient lighting.)

5-light race start sequence with a random delay

This project provides an simple F1 motor racing style 5 light race start sequence with a random delay that you can use on a real race track, kart circuit or even your slot-car circuit.

Peter says: "Operation is simple; when the start button is pressed all the LED clusters are off. They then illuminate sequentially at one second intervals until all five LED clusters are on. After a random interval between 1 and about 7 seconds the LEDs extinguish, signalling the start of the race. Once the LEDs have extinguished simply press the start button again to initiate another race start sequence."

Note, it is a complete application using 52mm LED clusters, but the software in the PIC microcontroller has been written to allow it to operate electro-mechanical relays, large arrays of LEDs, low voltage lamps, or even simply single 5mm LEDs.

You can view PCB artwork for the project. For those of you who don't have access to PCB making facilities Pete provides photos of building this project on stripboard.

Circuit description

"The circuit described on this page is designed around Kingbright's 52mm LED cluster module which comprises 50 red LEDs in a waterproof housing with a brightness in excess of 16000mcd," writes Peter.

"In the original version of this project each LED cluster was directly driven and all those LED's required a hefty current with the ten LED cluster version requiring a power supply capable of delivering 2amps at 12V DC."

In the new version of the project, he has written the software to provide three output drive modes:

• Direct drive - for use with relays
• Direct PWM - for use with LED clusters, driven by a PWM signal to allow control of brightness.
• Multiplexed PWM - for use with LED clusters, PWM provides brightness control, multiplexing reduces power requirements to < 500mA with 10 LED cluster.

This version also includes an optional isolated switch input. This uses an opto-coupler to allow the controller to be triggered from another system, to provide electrical isolation for safety reasons, or reduce the possibility of false triggering in an electrically noisy environment.

Construction Notes

Construction details for the PCB version are available. The PCB can be built up to drive either LED clusters or off-board relays but not both. There are a number of build options which require a choice to be made as to which parts are installed and these are described with the accompanying text.

Software

In terms of software, the PIC 16F684 microcontroller needs programming before use. Source code and programmer ready HEX files can be downloaded. But you can also buy a pre-programmed PIC from the On-line store.

Parts List

You can read Peter's extensive documentation of the project on his website, including a fully-detailed parts list.