Fade to dim

[Ytierian]

I'm looking to install a pulser circuit in a model I'll be starting soon.

Thing is, I don't want the standard - start at black, fade to full, fade to black.

What I want is a low-level glow at it's minimum, fade to full, fade back to the base low-level.

Can I adapt a circuit like this one http://www.redcircuits.com/Page51.htm ; perhaps by increasing R6's OHM value and adding a jumper from + through another resistor into D1 so that when the pulse is HIGH, the total power through R6 and the new resistor (call it R7) would match the normal R6 let-through?

Be gentle, I've been out of the electronics sceen for about 30 years

Ytierian

[jwrjr]

I would use a single-chip computer, which could do this easily. And the cost would be comparable to the circuit on the webpage. Of course the people who know of me are really surprised ...

[Sparky]

The pulse width modulator that is in the sticky thread can also be adjusted to do this. You can adjust the level that the triangle wave is swinging between and adjust the bias. In your case you want the bias very low, and the swing very small.

[Ytierian]

>>I would use a single-chip computer, which could do this easily. And the cost would be comparable to the circuit on the webpage. Of course the people who know of me are really surprised ... - jwrjr

And of course, though I've programmed anything from a C-64 to an AS-400, I have NO idea how to program single-chip units. I'm an old Basic/Cobol/RPG man, assembly language alway eluded me.

If you could point me to a web-site that describes how to do this, it would be great.

Could this circuit theoretically control more that one type of pulse/flash/fade, or would I need a chip-comp for each type?

>>The pulse width modulator that is in the sticky thread can also be adjusted to do this. You can adjust the level that the triangle wave is swinging between and adjust the bias. In your case you want the bias very low, and the swing very small. - Sparky

Thanks, I'll check that out and see where it leads me

- Ytierian

[jwrjr]

I'm rather fond of the PIC-type of controller, so I can give info about that. The manufacturer's ( www.microchip.com ) not only has info on the chips and application notes, but you can download the programming software (Mplab) for no charge. It even includes a C compiler. Of course the easiest way is to find somebody who does this already and get him to program it for you.
I wouldn't put more than 4 different controls (fades, strobes, flashers, etc.) on a single chip. It is possible to make more, but the programming starts to get a bit hairy.

[Ytierian]

>>The pulse width modulator that is in the sticky thread can also be adjusted to do this. You can adjust the level that the triangle wave is swinging between and adjust the bias. In your case you want the bias very low, and the swing very small. - Sparky

> Thanks, I'll check that out and see where it leads me

Ok, so I checked it out and have one (fairly) stupid question

If I'm running a pair of LED's off that (white 2.8-3.4v@20ma ea) I would assume (caveat on that) I have to change R6 to be more in line with the proper V/ma rating for the pair?

Ytierian

[Sparky]

Yes ,and you want to use a higher power transistor to handle the current, I use a 2n2222 metal case, it is 150 mA of drive I think. larger number of LEDs wired in from all over the model, can be used then. (we had 3 sets of nav lights, red and green pairs. if you do something like that be sure and wire the LEDs with their own resistor rather than the single R6, that way the red and green get the current/voltage they want (they aren't always the same).

[jwrjr]

I'm partial to power mosfets like the 2N7000 or bs170. One advantage is that you don't need a resistor in series with the 'base' lead. The bs170 is rated at 500ma and costs around $0.25 in small quantities. I use a s**tload of them.