Cheap UW flashlight to laser pointer conversion

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telemonster

Contributor
Messages
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Location
Northern Virginia
# of dives
200 - 499
This is a bit of work in progress. As I prepare to head on a dive trip with some friends from the laser show system community I'm going to (hopefully) convert a cheap underwater flashlight into a green pointer.

I found two existing units on the market. One is fairly expensive at $100, and it's unknown if it can be turned up or converted to run other modules. The other is a simple double A plastic pen pointer at Leisure Pro (and direct from China.) It looked like it might be an easy unit to convert but eh...

I chose a cheap metal light for the "host" that I found on eBay. It uses a standard 18650 battery and via ebay listing appeared to have some room where the reflector is. Also, the review indicated that maybe they have been underwater and didn't instantly flood, so maybe it will last at lease a few dives ;-) These are one of the many Chinese units that are all over the market.

The laser diode module which is still in shipping is a simple 100mw 532nm green with a driver rated for 3.7v. Duty cycle is noted at 1 minute on with some seconds off -- which doesn't instill confidence but YOLO. It would be nice to move up to the 200mw to 400mw range but I don't want to risk that kind of module on the project. I have some 1 watt blue laser diodes on the shelf but don't have drivers for them. Hmmmm.

The lights showed up early, so the first step is disassembly. The top part containing the reflector unscrewed without too much issue, and I'm working to get the rest out. Interesting on this light is that it is not activated by screw down of the head or pushbutton -- it has a settings ring. It looks like (so far) the settings ring moves a magnet around and that changes the modes. If this is indeed the case, that is pretty cool (until the magnet rusts out -- of course.) I expect to find hall-effect sensors inside or something, we will see. Cool for the light, but a bit more of a PITA for my project since I need to remove the existing LED driver electronics. I am still working on removing the existing electronics to make way for the new laser diode and driver.

I will post pics as progress happens. This is actually my 2nd underwater laser project, the first is one that uses a motor and a microcontroller to do PWM projecting various circle patterns out of an older Underwater Kinetics fixture that was meant for a 6v lantern battery. It will go on the trip as well, and it should actually produce "moon tunnels" and such for some interesting pictures. I went to test it over the summer at the local quarry (Lake Phoenix) and unfortunately the o ring to seal the unit was missing. I ordered a new O ring then found the one that was missing, so this should also finally make a voyage.

NOTE - the power output of this unit is above that which is eye safe as advised by the CDRH/FDA, and it will be used in a safe manner. Direct exposure of the exiting beam by people or animals would be bad.


Current pic of the housing (one together, one apart):
 

Attachments

  • flashlight2laser.jpg
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Weird. Clicking your imgur link gave me a virus warning popup

1st. Hooray for saxophone!

2nd. Oh no! Maybe you have an add on to your browser that warns about external links? It's just a photo on imgur, a commercial hosting site that started as a image dump for reddit. There should be low risk of malicious content on imgur. I tried briefly to add the picture on here but I didn't notice a way to easily add the photo. Will retry.

Edit: imgur.com link removed, image attached via sb!
 
The force is strong in this one.
 
1st. Hooray for saxophone!

2nd. Oh no! Maybe you have an add on to your browser that warns about external links? It's just a photo on imgur, a commercial hosting site that started as a image dump for reddit. There should be low risk of malicious content on imgur. I tried briefly to add the picture on here but I didn't notice a way to easily add the photo. Will retry.

Edit: imgur.com link removed, image attached via sb!

Yah, not sure the problem. Imgur hasn't given me issues before, but I appreciate you reposting.
 
Okay, a bit of an update.

The flashlight is interesting. As a flashlight, it is pretty bad. The linearity of the projected light is horrible, there is one small bright spot in the middle and then a large halo. So not a very good flashlight light output. The build quality feels nice though. But I would think the magnet used for mode selection might rust.

The mode selection is nifty, though. There is a magnet under the rotating collar that is read by 4 hall-effect sensors on the inside of the light. I think there is 6 modes, so it deducts the other two modes by the gaps. I wanted to use hall effect sensors on the bigger pattern projector flashlight (details coming after this retrofit.) There is a small circuit board with the microcontroller that reads the modes and drives transistors to run the LED light.

I will remove the LED, and the circuit board that is original. The best way I can figure to do things is I am going to use an ATTiny85 microcontroller to read a hall effect sensor, reusing the original ring control on the light. The laser module arrived, it's fairly long with the DPSS laser + driver that comes standard. I could relocate the driver but going to try to avoid to keep things easy.

I'm hoping to straddle the driver PCB with the microcontroller. I will build it into the neck part of the light and drill out or remove the reflector. I want the head part of the light where the reflector was to free rotate around the laser module / electronics when it is screwed back on.

The circuit will pretty much be the 3.7v LiPo battery feeding the ATTiny85 microcontroller, which is supposed to be fine. Hall effect will read the on/off, and output transistor to shift on the laser. Since the laser module claims to have a duty cycle of 1 minute on and 30 seconds off, I will software limit it to 50 seconds on. Also I will add a 5 second power-on delay similar to what a real laser projector has to meet federal guidelines. I intend to fuse the battery. I will make a cap for the entire thing or bag it so if the ring gets hit no big deal.

A friend send me some diffraction grating plastic as well, so that might make for some neat photos.

Once the electronic bits arrive and I make some progress will post pics.
 
Still waiting on the hall effect sensors for this project :-(

4 days overdue already.

If it has not arrived tonight I will eat it and buy one from Microcenter.

Hope to have progress this weekend followed by details.
 
Hall effect sensors showed up.
Got the microcontroller programmed and working, got the transistor figured out... and got it all assembled to go into the light housing.

Went diving with some people from the local scuba meetup group at a swimming pool today, and it was the perfect chance to try it out.

Except....

Last night, I was trying to get all the assembled bits into the flashlight, and get the hall effect sensor to read the magnet from the mode selection ring that came on the flashlight. It didn't seem to quite want to fit. Things were working, except the sensor position was tricky to nail down and the original custom made circuit board in the light made contact with the side of the aluminum housing which isn't something I could solder to.

In the process of this, something shorted out and a bunch of magic smoke came out of the laser diode driver board. EEEK!

I was hoping the damage was only a trace on the circuit board (it's never just a trace on the circuit board) but I can't really figure out where it went wrong. But something did. The smell lingered like a Cranberries song for 2 days.

The 18650 battery was getting real hot when this happened so that was by far and large my first concern. Tesla model S cards run on 6,900 of these batteries.... you get the idea. Kept the thing aimed away from me and pulled bits out.

PLAN B.

Two weeks until trip.

Replacement laser diode module ordered from China. Will it arrive in two weeks? Come on ePacket....

This time I will separate the diode driver and laser diode, putting the driver next to the diode module (the brass part in the pics.) This way it fits better.

I will send the output that went to the factory LED to a transistor to switch the laser on using the same mechanism. Hopefully the half brights and strobing modes (SOS) won't damage the laser.

This should allow me to reuse more parts from the factory light.

It will be close timeframe wise, will post updates.

In the meantime, the module setup that fried:

Flashlight retrofit.

\nn/
 
Been a while on this one. I haven't given up. I rebuilt a 2nd laser diode into flashlight using some things I learned. I left the original driver board, and tried to use the LED output to trigger a transistor to fire the laser diode. This way I could pull power straight from the 3.7v 18650 battery but use the original control board that reads the rotating magnet ring. It didn't seem to work. My guess is there isn't enough voltage supplied to the LED to trigger the transistor that I have wired to the laser diode. When I direct shorted it -- it still didn't work. Who knows.

Even with the diode driver relocated next to the laser diode versus behind it -- it's a tight fit to get it all into the flashlight.

I have decided to take a new approach. I'm not happy with safety interlock on retrofitting of a flashlight, though I kind of like the form factor.

The new plan is this:

Over my years of diving I have upgraded Canon Elph cameras. My original Elph died, but left me with this pretty nice case that only fits one old model of camera. My goal is to 3d print a plastic box the size of the old camera that will hold at least one if not two laser diodes, a microcontroller on a board with buttons and at least one 18650 battery. I think I might also be able to fit in a micro-servo that would allow a gratings filter or other effect to be swept into place.

Given that the camera has a lot of button push thrus, as long as I can line up a few buttons on the custom control board I should be able to use those to require a button sequence to turn on and off the laser. Small $3 OLED screen, $2 microcontroller, $3 servo, $20 laser diode, $3 battery. If I could find a better driver I could use PWM for laser power control.

Will report back on progress.
 
Best thread in months. I’m an electronics-head from way back so this is über-cool! Keep it going.
 
https://www.shearwater.com/products/peregrine/

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