LED headlamp project question/help.

[SmileDocHill]

Short version: Essentially there are 2 wires going to the bulb from the PCB. What problems could I cause by adding/splicing a variable resistor or potentiometer to the power wire between the PCB and LED to further control (dim) the amount of light. Could it be as simple as scavenging an inline volume control from earbud headphones and splicing it to the power wire? Can I assume the LED is "dimable" just because the single LED has 2 different outputs?

Before I start experimenting by trial and error I thought I would run the project by you guys. Plus I know this board is full of guys that like to tinker.

More details: I have a headlamp which puts out too much light.

https://www.tractorsupply.com/tsc/product/jobsmart-250-lumen-led-headlight?cm_vc=-10005

The circuit board and batteries are in the box at the back. The push button switch: push once= bright, second time= less bright, third time off. The difference between 1 and 2 is extremely little and both are too bright for my use. The LED is a Cree up to 250 lumen.
I haven't taken the multimeter to it yet to see how many volts and amps are going through the power wire to the LED for the 2 different outputs. The battery itself has a 5V output IIRC.

When I google it and see other people's LED projects that involve adding variable resisters or pot's they see loss of light output as a stumbling block but that is my end goal anyway. I also don't need to have a smooth transition from bright to dim, and I'm not worried about it going from bright to out in the top 10% of the adjustable range of a potentiometer.

 

[actaeon277]

LEDs don't really dim well if you try to treat it like a light bulb.

https://www.electronicproducts.com/Optoelectronics/LEDs/LED_101_How_do_dimmable_LEDs_work.aspx
Maybe this can help.


Also
https://www.digikey.com/en/articles...dim-an-led-without-compromising-light-quality

LED Tutorials - Installing a PWM Dimmer

 

[SmileDocHill]

Well, I knew they were different but not that different. Thanks for the links, that helps a lot. I kinda knew that at one point but one of my other led headlamps has an adjustment sliding arm that really appears to dial up and down the light like a volume knob on a sterio. I think once i saw that i hoped it would be that simple.

 

[actaeon277]

Well, I knew they were different but not that different. Thanks for the links, that helps a lot. I kinda knew that at one point but one of my other led headlamps has an adjustment sliding arm that really appears to dial up and down the light like a volume knob on a sterio. I think once i saw that i hoped it would be that simple.

That slider bar may just be input to a pwm device.

You can dim LEDs with a rheostat.. sort of. It doesn't work well, though I imagine there are people that are out there that have done it.

I know I did it, but with a PIC chip. The rheostat would be the input device to the chip, telling it what level.
Then the PIC chip pulses the LED. For instance, 50 milliseconds on, 50 milliseconds off. (or maybe it was microseconds, I can't remember.
Then, by changing it to 80 milliseconds on, 20 milliseconds off, you have brightened the LED.

 

[1911ly]

ACT is right. LED's to not react the same way as a light bulb. It doesn;t turn on until the diode conducts. You can find a sore of tipping point where it dims a bit. But it is not stable. PWM as ACT discribts (pulse width modulation) is the correct way of dimming them. The diode is turned of and on rapidly. Changing the length of the on and of time changes how much light is emitted. You can buy controllers and software to control them or build your own but that is not practical for most part.

 

[Mr Evilwrench]

I saw the thread and was going to chime in with PWM. That's really the only way you'll get good performance, efficiency, and not burn the element on your variable resistor. It's well possible to make a PWM dimmer with a slider, in fact one year I made a SIMs hat for my son with the little crystal over his head. I set it up so he could go to the door with the light red, and adjust it through yellow to green as he got the candy (red + green = yellow). It worked out real smooth with the slider. The whole thing was a hex Schmitt trigger inverter plus transistors to drive enough current, and resistors and capacitors.

 

[actaeon277]

https://www.jameco.com/shop/StoreCa...001&freeText=led dimmer&search_type=jamecoall

 

[gmcttr]

Ask here... CandlePowerForums they will know.

 

[jsharmon7]

Good luck, Doc! I’d probably just buy a different headlamp and move on with life.