Idea: easily adjustable current for a small build

I don't know if this is a horrible idea or if it has already been brought up and shot down, but what if someone made a laser that had some sort of knob that would allow you to adjust the current without opening the thing up? Perhaps it would be soldered onto the pot or something, and you could somehow limit how far you could turn it. Or maybe you could have 2 current limiters of some sort, the first wouldn't be adjustable and be set to the maximum for the particular diode, and the second would be adjustable by the aforementioned knob.

I have been thinking about this because I'm putting together a 12x diode blu-ray build, and it would be nice to have just one laser for each wavelength to carry around, and not have to lug around a burner, a beamer, and a pointer. I probably wouldn't try this on this one, but perhaps on a future project. What does everyone think of this? Has anyone tried it? Am I just being a noob, and should I stop bringing up stupid ideas?

Totaly doable and it has been done, I seen a video here or on U-tube. why would any one want such a laser ? to save the diode for long life when you wern't burning up stuff ?

Sure, you can build an adjustable current driver and have a potmeter that you can turn without opening the laser - although the case would have to be fairly large to fit one. A slider switch might be more easy to build into the host with a low and high setting.

Turning power down makes it more usable in some cases, such as when actually using it as presentation pointer... and it saves battery life too.

Cool! I was thinking this would be a good idea because then I could make my 500mW somewhat safe to use indoors around somewhat reflective surfaces, without needing to carry around a second moderately powered laser. I also don't think it would be a great idea to use a power monster as a presentation pointer, as Benm pointed out.

Well, with a green build, you could drill a hole into the case precisely where the pot is, the slice off the tip of a screwdriver that's big/small enough to fit into the pot, then add some glue to the tip of the screw driver, put it in the pot, let it dry, then use that (possibly put a button type fixture on the end of the screwdriver device) then 'screw-in' the power (that whole thing was full of 'thats what she said jokes') And, on the pot, you can have a clicker device (like on Wheel-of-Fortune) that would click when you turn the pot. So, one-click is say...+25mW, for every click it would add 25mW. But, that would be different per diode, per driver, per pot, so this is something that would need a large amount of testing. OR, you could have little metal 'fingers' like the 'Tin Wiskers' phenomina that would keep you from turning any further which would right below the maximum (not the actual max, because then the diode would die there). Anyway, I should stop there...I got a million ideas, just not the ability to put them into work. I'm still looking for a high powered green line generator, a fog machine, and a flat tipped super soaker....

Those are good ideas. I was thinking about something like that. Maybe I could find a really really really small ammeter, disassemble it, and somehow stick it in there after the driver, so it would display what current I'm giving the diode as I adjust the driver with the screwdriver knob thing. The biggest problem with all of this is determining how much current you're feeding the diode, because you can't just blindly turn that pot.

I just made another idea! If I were at all knowledgeable of electronics (which I'm not), I could wire it to some LEDs that would run along the side of the host. I'm making a 12x blu-ray, so this should produce about 450mW (conservative) to 500mW (moderate). I don't have the burner yet, so I haven't been able to test the efficiency of the diode, so I don't know what current would be able to produce the following outputs.

For my build, this is what I might do. Once the current hits a certain low level that would let the laser run at a safe 5mW, the first one would turn on. This one would be white or something. Once the current hits a second level that would let it run at 30mW, a blue one would turn on. When the current would produce an output of 100mW, the green would turn on. At a current producing 400mW, yellow. At a current producing 500mW, it could be red. Once a user sees red, they should stop turning.

A third practical idea: There's probably some sort of small device out there that would automatically break the current at a certain level. For me, this could be whatever current would produce 500mW. Though this wouldn't be nearly as cool as the LEDs, it might actually be possible with my electrical skills. Or maybe at a certain current, it would switch to a second sub-circuit with another driver that would hold the current down to the maximum safe level.

It is usually not too hard to "hard wire" a maximum current limit into a driver - for a linear (DDL) driver, you simply put a resistor in series with the potentiometer. The resistance of this, plus the minimum resistance of the pot, will directly set the maximum output current. With a bit of calculation, this can be used to make a driver adjustable but still have an upper-end limit that won't kill the diode.

Someone who isn't electronically retarded like I am! This might actually work!
Would I just try a bunch of different resistors until I found the right one that would give the right upper current limit, or is there a formula that would determine what power resistor I should use to get that max current limit? Is there a simple conversion factor between I/O current and resistance that I don't know of, or am I going about this completely wrong? See my signature. :yh:

bloompyle said:

Well, with a green build, you could drill a hole into the case precisely where the pot is, the slice off the tip of a screwdriver that's big/small enough to fit into the pot, then add some glue to the tip of the screw driver, put it in the pot, let it dry, then use that (possibly put a button type fixture on the end of the screwdriver device) then 'screw-in' the power (that whole thing was full of 'thats what she said jokes') And, on the pot, you can have a clicker device (like on Wheel-of-Fortune) that would click when you turn the pot. So, one-click is say...+25mW, for every click it would add 25mW. But, that would be different per diode, per driver, per pot, so this is something that would need a large amount of testing. OR, you could have little metal 'fingers' like the 'Tin Wiskers' phenomina that would keep you from turning any further which would right below the maximum (not the actual max, because then the diode would die there). Anyway, I should stop there...I got a million ideas, just not the ability to put them into work. I'm still looking for a high powered green line generator, a fog machine, and a flat tipped super soaker....

Click to expand...

I'm not entirely sure, but touching the case of the pot to the case of the laser would short the circuit out wouldn't it? The laser wouldn't work at all if any metal of the screwdriver was touching the case.

At least I'm pretty sure it wouldn't, can anybody fill me in who knows for sure?

Pontiacg5 said:

I'm not entirely sure, but touching the case of the pot to the case of the laser would short the circuit out wouldn't it? The laser wouldn't work at all if any metal of the screwdriver was touching the case.

Click to expand...

You're probably right. I have no idea whether the pot case connects to the circuit. Maybe it does in only some models. :thinking: I need to find a carbon fiber screwdriver... :banghead:

Maybe if I just filled in the screwdriver slot in the pot then glued a nonmetal little rod to the filled in pot. Then I could attach some kind of knob that one could turn to the end of that rod. I don't know how cleanly that would come out, but it's plausible.

I still need to figure out how to set that maximum current limit... Does anyone with any electronics experience know what kind of resistor to use with if I'm using a MicroBoost driver and I want a maximum current limit of 350mA?

If you use the lm317 circuit, get a fixed resistor in series with the pot. I'm not familiar with the microdrive circuit, but if you can post a schematic of the thing i'd be happy to suggest required modifications.

There are some nice stick-in and glue-on control rods/knobs on the market, so there is no need to cut up screwdrivers either.

or..... simply put a second pot in series with the output lead between diode and driver. When you turn the second pot down, it will lower the current to the diode then when you set the second pot to full... it will output the value of the driver.

:beer: -Adrian

bobhaha said:

or..... simply put a second pot in series with the output lead between diode and driver. When you turn the second pot down, it will lower the current to the diode then when you set the second pot to full... it will output the value of the driver.

:beer: -Adrian

Click to expand...

No, that will kill the diode if the diode looses power and then suddenly gets power again from the wiper falling off or shorting. Never put anything between the driver and diode.

Its been done before...

http://laserpointerforums.com/f38/new-ggw-6x-mini-1xaa-energizer-host-dimmer-45817.html

BTW what do you think happens in TTL modulation??

Dimming in TTL modulation is done by changing the resistance on the driver I thought.

I know I've read in many places that a pot directly in series with a diode will lead to a dead diode.

I don't see anything in that thread about dimming with a pot in series with a diode ...

It was mentioned in another thread that he used the stock "setup" meaning pot and boost driver from the host then added a driver for constant current.

Well then just be be sure we should ask for third party input... because I"m not 100% sure and can't fully support my idea.