Untill this Xmas, my small exterior Xmas lights display has been the pride of the street, consisting of no more than a few ropes light, put up in a big tree growing outside my house.
That was untill without warning, a neighbour produced a Xmas light display based on a Xmas tree shape frame, with about 5 sets of flashing xmas lights, measuring some 3 metres high and 2 metres wide, the bugger spoilt my Xmas.
This has meant that I now have no choice but to produce something bigger and better. I am starting early, so that I can get things right and not take up all my time in one go.
I managed to buy on Ebay from Hong Kong 10 sets, for £5 a set, some LED based light strings consisting of alternative blue then white LED's, run by a 4 channel light controller. They are 5 metres long and consist of 50 white and 50 blue LED's. The controller supplied with them, does quite a nice job of running things, but I want to create something that my neighbour will not be able to compete with (I hope).
My idea is to run down from the apex of the roof, hanging over the gutter and down the front of the house, the 10 sets of lights, evenly spaced along the house. I want to run them from my own design of PIC controlled light controller. I do not want to rewire the 1000 leds I have, so will compromise on only having full control of the individual light strings in the horizontal axis, and only having control of the 4 channels in the vertical axis. this of course equates to 40 channels of light control. I can handle the design on the PIC side, but just want to check with you all that I have the theory right on how the LED's are driven.
The controller which came with the lights, consists of a bridge rectifier, no transformer, 4 thyristors, some sort of dedicated MPU board which has an encapsulated IC of some sort, a simple resistor/capacitor power supply for the MPU, a resistor/button going into the MPU (to change the patterns) and thats all. No current limiting that I can see, nor voltage regulation. On checking the LED strings, they consist of 4 lots of 25 LED's wired in series. Nearly every LED in the first 2 metres have a tiny 3K resistor wired into one of the legs, the last 8 metres are directly wired. Thats 18K of resistance in each of the 4 channels.
Do you think it is safe to switch each of the channels with Thyristors directly with mains power or is their some deep dark mysterious driving taking place, within the MPU?
I have some 64 pin PIC's I have used in the past, which I could use to simplify the PIC coding/circuitry, Or do you have any suggestions on how to drive 40 thyristors differently with a smaller PIC? Obviousley component cost is an issue.
Mad Mark in Spain