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Registered Member #326
Joined: Sat Mar 18 2006, 01:12PM
Location: Glasgow, Scotland
Posts: 66
The Concept:
3 spotlights, one red, one green and one blue. Initially the red light is switched on to maximum brightness, the other two are off. Gradually the red light's intensity drops, with a corresponding increase in the green light's intensity. The green light's intensity rises steadily to maxiumum, as red drops off to zero. The same transition then takes place from green to blue, and then from blue to red and the process repeats. The directions of spotlights are adjustable such that if they are all focused on the same spot on a wall or ceiling they will produce an area of light of constantly changing colour.
Alternatively the light beams can be directed to different points to create a swirling effect. All sorts of effects are possible depending on speed and where the light beams are aimed.
Implementation:
The circuit is controlled by a Microchip PIC16F84A, which is clocked by a 4MHz crystal. Output pins A0, A1 and A2 on the PIC each drive one light. One red, one green and ine blue 50W low-voltage dichroic lamps are used. Each of the 3 lights is powered from one of the four isolated 24V AC windings of a 220v-to-24V lighting transformer. The drive circuit for each light consists of a BC547C NPN transistor driving a pair of BUZ10, BUZ11 or IRF610 n-channel power MOSFETS. Two MOSFETS must be used in series, connected source-to-source, as a single MOSFET would conduct on one half-cycle when in the "off" state, due to its internal drain-to body diode junction. The transformer's fourth winding drived a bridge rectifier and smoothing capacitor, which in turn supplies 5V and 12V linear regulators (7805 and 7812) which supply the PIC and NPN driver circuits respectively.
Circuit Schematic. Note that only one lamp and driver circuit is shown, the other two are identical.
Prototype. PIC and driver circuit in centre. Each MOSFET is attached to a separate heatsink.
The project is programmed in PIC Assembler, compiled via MPLAB IDE v7.51 and downloaded via PicKit 2 Debug Express, with v2.10 PC software.
This is the current version of the code:
I don't claim that my component choice or indeed my coding is in any way optimal, I've largely used what's to hand and my programming skills are pretty rusty.
Planned Developments:
I'm looking for ideas for a case for the project. I'd like to recycle some old piece of equipment. The case must be large enough to accomodate the 150mm diameter, 100mm high transformer, and 3 110mm diameter spotlight mountings. I'm thinking about an ammo box perhaps, or maybe something more sophisticated-looking. It would be nice to have something elegant looking. All suggestions gratefully received.
I plan to add a user interface and code enhancements to allow the rate at which the lights cycle through the range of colours to be adjusted over a range of around a seccond to many minutes. This could be implemented using anything anything from thumbwheel switches to a diplay from and old cellphone with pushbuttons.
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Spotlights Projecting Constantly-Changing Coloured Light
