"Terry Collins" <
[email protected]> wrote in message
news:[email protected]...
> hippy wrote:
> >
> > Spotted this dimmer switch on Phantom:
http://www.phant-
> > omcycles.com.au/Content.asp?S=Details%20@ID=1553
> >
> > What would be needed to make your own and how much do
> > you reckon it would cost?
> >
> > It'd make my 15w globes a bit more useful but I don't
> > wanna pay $70 for it.
>
> Supposedly[1] you can make a dimmer from 2 x LM311 1 x
> MTP3055E 1 heat sink for above 4 Resistors 2 x 10K, 1 x
> 22K & 1 x 220K 1 Pot 20K-50K 2 signal diodes 1 x 330pF Cap
> piece of vero board
>
> 1 double matchbox size box (optional)
>
> [1]A mate turned up with it. Firstly for help to lay it
> out on the vero board, then for help to get his
> soldered creation working. We ended up stripping
> everything off the board and trying to get it working
> on a protype board.
>
> Lets just say after him telling me that he let the magic
> smoke out of the 50K pot (boogle), I wasn't surprised when
> nothing worked on the protype board.
>
> It basically is a oscillator that feeds a PWM that pulses
> the MTP to turn the light on and off. The pot varies the
> duty cycle. He says he has seen one working and the the
> freq is 800Hz, but basic RC calcs say 13KHz and simple
> circuit analysis says about 20KHz. Unfortunately, neither
> of us has a scope to see this.
>
> At this stage, I think he has an incorrect circuit diagram
> an I can not find any similar circuit. If anyone knows of
> an op-amp oscillator circuit that ties the output to both
> the inverting and non-inverting inputs with diodes, then I
> would like to see it.
>
>
> End story, if I get something working, then I will post a
> circuit.
There's a simple circuit for an oscillator here, on page 12.
You might need to fiddle a few components to get the right
frequency.
http://www.national.com/ds/LM/LM111.pdf
Marty