I have posted this topic on here before, but haven’t got quite the right advice on the matter. I want to add a dimmer knob to my light. I believe I will need a potentiometer, and a single mode driver. May need a resistor as well. Can anyone steer me in the right direction??
Sounds like a very cool project
Subbed!
It’s been a goal of mine to figure it out. There are a few predator hunting lights, Coyote Light and Wicked Lights, that offer this option, so I know it’s certainly plausible.
You can buys lots of different lights with rotary brightness controls. Most of them are a lot more sophisticated than a simple potentiometer. But if simple and diy is your goal I don’t see why you’d need anything else. As long as your emitter matches your cell voltage it should work with just a pot in series, yes? You wouldn’t have any sort of lvp or regulation, and certainty no boost as your battery dies, but it’ll light up.
At least, I think it will. Never done it myself.
There are a lot of diving lights on the market with stepless dimming with a short slider (magnetic, not a potentiometer).
They’re not even expensive.
But i don’t want to gamble on the visibility of the PWM.
This one seems interesting:
http://www.kaidomain.com/p/S025088.D170-Cree-XHP70-Neutral-White-4000K-4000-Lumens-Stepless-Adjusted-Diving-LED-Flashlight-Black
This is said to work well:
http://www.ebay.com/itm/172055327012?\_trksid=p2055119.m1438.l2649&var=470911703344&ssPageName=STRK%3AMEBIDX%3AIT
I don’t know how it’s typically done, but I came across this linear regulator chip, the CN5611 that I think could work well. It is sort of like a 7135, but it can do 800mA and you can adjust the regulated current with an adjustable resistor.
It wouldn’t be any more efficient than just putting a high power adjustable resistor in series with the LED, but maybe easier to implement… I don’t know.
If you go with the simple high power adjustable resistor route, the resistor would have to be adjustable in the range of ~0-10 Ohms and be able to dissipate ~1-2W, or more for a higher power light. For a single XPL type LED, it would be direct drive with the resistor set to ~0 Ohms, and would limit the current to ~0.2A when it’s set to around 10 Ohms. It would require much more resistance to get to very low current “moonlight” levels; it is not a linear relationship between the resistance and the current. For this reason the regulator I mentioned above might be more practical.
You could do it with a buck driver. Just yank the MCU and wire the potentiometer between the Vin pad and the PWM out pad. Or, maybe better, would be to short those 2 pads and replace the sense resistors with the potentiometer. The potentiometer would need to be able to handle the wattage though. You would need to lock out the light when not in use.
Here is my thinking on this subject:
- I would find driver with nice big current sense resistor
- I would measure current draw in highes mode and determine if there is a place to push that driver for higher output by lowering the value of sense resistor resistance (by adding more resistors in parallel setup) this should provide me with max and min values for current sense resistor
- then I would desolder that resistor
- i remember I watched a video on youtube that explains how to use one or two additional potentiometers to set top and bottom values of your main potentiometer, this would allow you to use full travel (full scale) of your potentiometer not just one small part, well I would find that video again, make that potentiometer hack and solder it where current resistor was soldered
- for testing I would use mostly depleted cell, if it works go full throttle with fully charged cell
Edit:
If you could find driver from Crelant 7G5CS that one would be good for experimenting because when you supply voltage to that drive it will alway turn in highest mode, if you want to change mode you have to click e-switch so if you remove e-switch you have driver with one mode -> max and it has curent sense resistor 
The CN5611 has a rather big voltage drop unfortunately.
That would be fine for higher voltages though, but not for a single cell.
Just PWM the plus of the 7135s and it’ll work.
Thatś what AK47 and 105 drivers etc. do too.
You could probably make it work with any pot that would handle the watts. An old school wall dimmer from your home improvement store would work. But a pot converts power to heat, so it would be hell on the batteries. So you should go PWM. You can build these circuits yourself, but it probably wouldn’t fit inside a flashlight unless you have a custom circuit board. But that’s expensive and hard. So your best bet is to just shop for a flashlight with a dimmer knob or dimmer slider control.
I’m all for taking the easy way out. If I could hi-jack a driver from another light to work with mine. Thing is it would have to be 1.5A at most. There’s a company called wicked lights that i believe makes a single cell light with a dimmer knob in the tailcap.
Here’s a link to an upgrade kit for their single mode lights. Almost thought about buying it just to see how exactly it works.
That link doesn’t work for me, but I googled it and found this website. They literally call it a rheostat right on the page. Its an analog potentiometer, old school. Functional, but probably very inefficient.
Or maybe they’re doing something smarter than I’m seeing.
Yeah, I’m not sure. As I said, I almost actually bought the upgrade kit just to dissect it. I thought there were a few places that you can have a custom board made, and you can wire in a pot.? Some of the stuff mentioned above is a little above my skill level.
Ah, you are thinking PWM controlled by a pot. That is possible with a 555 timer chip, or some high-end programmed chips, but not the basic chips you normally find in a flashlight.
The pot would be in control of the duty cycle by draining a cap at whatever rate it was set to. The 555 would turn that into a duty cycle (PWM).
On a programmable chip, ADC would be where you connect. The pot would be wired across power and ground, therefore giving any voltage in between on the tap wire of the pot. That would be connected to ADC, and the chip would read the voltage level. If it was set at 2v on a 3v scale, then the software would compute that to be 66% brightness, and then create the PWM output with a 66% duty cycle.
Any links to a programmable driver that will except a pot?
Come to think of it, any attiny13a driver could probably be reprogrammed to work like that.
Someone said earlier you could do it with a buck driver. Would this work??
Well that one has no pictures or mention of what chip is on it. I was going to dig up a link for you last night but was so ready for bed.
Here’s what I like:
17mm Driver
The 7135 can just not be programmed at first, then if you find you want to program it to take over below a certain brightness for lower lows, you can do that with a software update.
I only chose the 17mm diameter because your last link was that size. You need to share the host specs or I don’t know how many LEDs you are driving or with what voltage.
But before you buy anything, ask one of the programmers on here like ToyKeeper if she already has a firmware that works like you want. If so, be sure you buy something that accepts her firmware. If not, be sure to buy something you or your programmer can work with.