This is not a thread about running.

For a project I am working on and have a 12V, 100mA control line. I want to power a bunch of 12V leds with an external source. I could just put a relay in and be done with it, but I want to make said LEDs dimmable. I don't care if it is linear or step fading.

I'm not real familiar with relays. Is there such thing as a progressive relay? Do I need to regulate the voltage or the current for this relay that may or may not exist? I have several control lines so current is easy to get more of. I don't think the control line will let me reduce regulate the voltage.

Thanks.

Does the control line simply switch the LEDS on and off and then something inline with the external power source control the dimming? It's not practical to use several relays for several LED's. You're much better off using FETs.

I'd try using some transistors as shorts across resistors. i.e. have a set of however many dimming levels you wanted with a transistor and resistor in parallel. When you want full brightness, source through the transistor, shorting across the resistor, when you don't want that level of brightness, turn transistor off and go through the resistor. The same could be done with relays, but they're gonna be large and require a 24dc or 120ac source.

Resitor
---/\/\/\------------...... repeat until desired amount of dimming is achieved
| |
----( )-----
Transistor

Maybe even easier would be to just have a series of resistors with shorts to line at each connection. This way each time the next line switched on, the voltage would have fewer and fewer resistors to go through


---/\/\/\---/\/\/\----/\/\/\----LED
+12V....+12V...+12V.....+12V

Each one being a seperate switched 12V

How fast can the said 12V control line be changed? If you could control it fast enough you could make it PWM dimmable, meaning that you control the led string with a high frequency square wave and adjust the pulsewidth of the on vs off period of the square wave.

You could use a simple transistor or n-channel mosfet with the gate controlled by the 12v control line through a resistor in this case.

I'll bet if you used a lighter baton it would get there faster. OOOH and paint it red too! That always makes things go faster.

you can use a relay to turn them on then use resistors to dim them, an adjustable pot would work just fine.