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FrozenGate by Avery

First build, custom driver advice?

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overambitious

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Jun 8, 2018
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I recently broke my first laser pointer, a 75mW 405 Wicked Laser Nano that a friend gave me. Naturally, I've chosen to replace it... with a fully custom 2W 462nm build.

A key feature that I want is the ability to adjust the current in use, I've found plenty of adjustable drivers so far but they all rely on tiny 10-turn trimpots that aren't designed to be accessible when mounted. Ideally, I want a handheld laser with a knob that will let me change it from 'stupidly dangerous' to 'mildly irresponsible' and back without having to crack it open in between.

I have a couple main questions:
1. Is it bad for the health of the diode to run it at low current? It's nominally a 2W diode at 1.8A, but the testing images show it functioning at 25mW at 200mA. Is this an acceptable way to run it in everyday use, or only for brief periods while showing the response curve?
2. Is it bad for the health of the diode to adjust the current while it's operating?
3. Am I going to need to make a full driver board, or can I just cut the 10-turn pot off an existing one and run new wires to a new pot?

I'll be doing all of my testing with a 2W 445nm diode since it's about 1/5 the price, and I bought a benchtop 50-3000mA driver that looks pretty simple but won't fit in a reasonably sized host. Ideally, I'd love the finished version to include a tiny arduino of some sort with a readout for real-time current draw and approximate wattage. If there's a reason that's very doable or very impossible, I'd love to know about it.

Thanks in advance for your help!
 
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I should add that I'm a mechanical engineer by trade, with limited experience with circuits and software but access to a full machine shop and EE lab with professional equipment. I'm taking on this project to get a bit better with circuits (and probably LTspice in the process), and hopefully some basic arduino programming too. Because it's about learning (and having an awesome blue laser), I'd rather do things the right way than the easy way.
 
1. No, that's fine.
2. It's not advisable to change the current setting with the laser running.
3. To expand on the last point, you really want to use a driver that supports analogue modulation. Those drivers take a 0-5V signal and adjust the current between a minimum and maximum set pointed based on the input voltage. 0V = minimum, 5V = maximum.
 
So based on some more research, it sounds like I want to buy/make an analog driver board rather than the TTL driver I already ordered (damn!). The information about analog vs TTL seems mostly oriented around driving multicolor arrays for light shows and precision waveforms for scientific research, but not well suited to people who are just trying to make a laser pointer.

I'm going to state a bunch of my beginner assumptions as facts, and hopefully people will be able to confirm/refute them without thinking I'm too much of an idiot.

- For an adjustable TTL driver, you have the binary option ON/OFF, where ON is whatever current you set beforehand with the trimpot.

- For an adjustable analog driver, you have a maximum current of [whatever], with 0%-100% control limited only by the resolution of your control potentiometer.

- Modulating a TTL laser while it's on is bad, but modulating an analog laser while it's on is fine because that's literally what the circuit is made for.

- I can replace the current adjustment trimpot with some sort of arduino-controlled circuit that will allow me to control the laser frequency in software with limits that will make it safer to play with.
 
What gave you the idea that modulating the TTL input of a driver is bad for the laser diode? It is not. It is much better than changing the current of the diode on the fly. All you need to do it use a PWM and vary the pulse width.
 
No, I was referring to modulating the current of a TTL laser while PWM is at 100%, which I still assume is bad. My reason for wanting actual current adjustment is that I assume that for most casual use I'd want to keep the output power low enough that the PWM would be obvious.

Would it be okay to have internal switching that runs TTL at 100%, then shuts it off before the amperage change, and then immediately restores power? My goal is to be able to reduce the emission to a safe continuous beam (low power, 100% PWM), rather than an infrequent blinding strobe (100% power, low PWM). Is there a reasonable way to do that?
 
There is no need to use TTL at all if you are running it at 100%. There are drivers that have analog modulation that is safe for your laser diode. Varying the current on the fly by adjusting the current set pot is not, however.
 
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I guess I've been unclear. What I'm trying to achieve is a handheld laser using a 2W diode, that can be given a user-selected current to produce a continuous beam of variable strength ranging from 'amusing toy' to 'engraving tool' with the adjustment of a knob on the housing. It would be nice if the power could be adjusted while the laser was firing, but is certainly not necessary.

As I understand, this sounds like a build that is more suited to an analog driver than a TTL driver. Additionally, I'll probably have to create some circuitry (or arduino code) to interrupt the laser beam while current adjustments are being made.
 
I believe there are some Black Buck drivers that would meet your needs here. They have a place where you can solder the leads from a pot to the driver for adjustment of the power. I'm not sure if it is required to turn the laser off before adjusting it, but it is ready made to do this.
 
overambitious said:
I guess I've been unclear. What I'm trying to achieve is a handheld laser using a 2W diode, that can be given a user-selected current to produce a continuous beam of variable strength ranging from 'amusing toy' to 'engraving tool' with the adjustment of a knob on the housing. It would be nice if the power could be adjusted while the laser was firing, but is certainly not necessary.

As I understand, this sounds like a build that is more suited to an analog driver than a TTL driver. Additionally, I'll probably have to create some circuitry (or arduino code) to interrupt the laser beam while current adjustments are being made.
Click to expand...

paul1598419 said:
I believe there are some Black Buck drivers that would meet your needs here. They have a place where you can solder the leads from a pot to the driver for adjustment of the power. I'm not sure if it is required to turn the laser off before adjusting it, but it is ready made to do this.
Click to expand...

You can adjust the power on the fly while the diode is on. That's the whole point of having analogue modulation.
 
I thought the BB driver could be adjusted while on. Just wasn't absolutely sure, so I added that qualifier.
 
paul1598419 said:
I believe there are some Black Buck drivers that would meet your needs here. They have a place where you can solder the leads from a pot to the driver for adjustment of the power. I'm not sure if it is required to turn the laser off before adjusting it, but it is ready made to do this.
Click to expand...

I see this on the Blackbuck 8, but not 6. In both cases though the datasheet has a lower limit of 1000mA, which makes sense for an engraver or something but doesn't do me much good here. This is what I got for my benchtop, which claims 50-3000mA. Definitely not going to fit in a handheld host :/

I found references to X-drive and X-boost models with 150-1800mA ranges, but nothing that's in stock. Any thoughts on where I should be looking to dig up something in my range? I'm also happy to build it myself and comfortable with soldering, but I don't know a damn thing about circuit design.

EDIT: Am I grossly misunderstanding this? The other interpretation is that the blackbuck driver is setting the MAX, and then the analog pot lets you go 0-100% OF THAT VALUE. Which would mean that I could use a blackbuck 8 to drive an analog laser from 0-8000mA, or from 0-1000mA, but not 0-250mA without burning it up if I went above 25% (or some threshold value).
 
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As I understand it though it should be fine, since I want to have analog control over a 1.8A diode. I would have issues if I wanted to use that driver for a 250mA diode, since I couldn't run the analog signal to 100% without frying it.

Can someone please confirm or refute this?
 
I'm just gonna go for it! I just ordered the blackbuck 8 and already purchased a cheap 2w 445 diode, so it's time to head to the test bench and see what happens. I'll report back if it fails to run under 1000mA (or fries).
 
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