Low-power cyan laser integrated into laser presenter

[bjp]

Hello,

I am interested in integrating a low-power cyan laser diode into an existing commercial laser presenter (like a LogiTech R400 or DinoFire DG100). I am talking about ~5mW.

This presents two issues:

1. How to get a cyan diode at that low of power. Certainly the best diode option seems to be the Sharp 488nm. I saw the thread “Sanity Check on Proposed Low-Power Cyan Diode Laser Build” by imallett (sorry, can’t post links due to low post count). It seemed like consensus was that it wasn’t reasonable to run at that low of power, but perhaps it could be lowered to 10mW and use ND filters. I’m curious if anyone had more thoughts on the matter.

2. Replacing the diode in a commercial laser presenter is nontrivial. The only example I found was this LogiTech R400: [can’t post links due to low post count, google “tutorialostv Disassembly of Logitech R400 Presenter to replace laser diode” and it’s the first item] but it seems that not all of the units have separate driver boards. In fact, some R400s do not have separate drivers: [can’t post links due to low post count, google “ifixit logitech R400 presenter disassembly” and it’s the first item]

Also, I opened up a DinoFire presenter unit I own and saw that its driver is integrated into the main board and does not have trimpots. Anyway, if anyone has advice on how to do this, on someone else who has done this, or if it is even possible is very appreciated.

Thanks in advance!

 

[paul1598419]

The Sharp diode would work well for this, but you likely won't be able to use the driver that came with the pointer you want to use. You will want a driver that can supply a fairly high forward voltage at/around 75 mA. That current is not meant as an indication of the forward voltage, however. These diode just have a high forward voltage. That was my point.

 

[Spoomples]

1: 80mw through an ND16 filter = 5mw. You may need a laser power meter, or someone with one that's willing to adjust the power for you, to verify that the power getting through is actually ~5mw.

2: Its extremely unlikely that the driver in a red laser pointer will work on such a radically different diode, you will have to wire in an appropriate driver (LDSE500/ACS1500SE) somehow. You'll also probably need a very small, non-standard host for the diode in order to cram it in there (like this fancy one, or these cheap ones). Test the voltage of the lines leading to the stock driver to see if they supply enough voltage, then maybe test if they can provide the needed power without smoking (using a resistor as a load). If it can't, you could try connecting the new driver directly to the battery, with a transistor/MOSFET as a power switch.

 

[bjp]

1: 80mw through an ND16 filter = 5mw. You may need a laser power meter, or someone with one that's willing to adjust the power for you, to verify that the power getting through is actually ~5mw.

I have access to a power meter and can verify myself. But should I worry that that will drain the battery quickly or create too much heat?

2: Its extremely unlikely that the driver in a red laser pointer will work on such a radically different diode, you will have to wire in an appropriate driver (LDSE500/ACS1500SE) somehow. You'll also probably need a very small, non-standard host for the diode in order to cram it in there (like this fancy one, or these cheap ones). Test the voltage of the lines leading to the stock driver to see if they supply enough voltage, then maybe test if they can provide the needed power without smoking (using a resistor as a load). If it can't, you could try connecting the new driver directly to the battery, with a transistor/MOSFET as a power switch.

Thanks.

 

[ZRaffleticket]

I think your concerns are valid for heat / power consumption. Especially since this diode wasn't designed for what you have in mind... specifically, you don't have a lot of room to put something capable of dissipating a ton of heat.

For the most part, what Spoomples suggested is what I'd say to go with. First, buy one of the tiny housing modules to fit the diode into. See if that fits inside your host. If it doesn't, don't waste your time/money on the rest.

If it fits? Good - going on from what spoomples said, instead of starting at 80mW you can look into reliable drivers and see how low output you can find and trust... I'll give an example of one of the more common drivers we use on these diodes:

You could use the existing internal circuit to drive some sort of mosfet to something in parallel driving the actual laser. The laser driver would use the micro flex drive which has a minimum output rating of 65mA. According to DTR's testing of the diodes, that would put the diode output at around ~25mW - which is not quite eye safe yet so you need to get that down to 5mW or less with some sort of ND filter. So you'd need a 20% transmission filter (OD ~0.7).

I'm not sure if these diodes can output 5mW after the lasing threshold or not.... but if you choose to use a different driver setup and still require a ND filter, use the following formula to derive what OD is needed on your ND filter:
OD = -1 * LOG10(transmission%).

But in general for something tiny like this, keep the power as low as you can.

 

[bjp]

:
You could use the existing internal circuit to drive some sort of mosfet to something in parallel driving the actual laser.

Can you really drive a mosfet with a current source?

 

[paul1598419]

It sounds to me like Zach is saying the MOSFET would be used as a switch using the existing circuit in the host to power the driver. It can certainly do that.

 

[ZRaffleticket]

Yep. I think the body diode in the mosfet would be enough of a load for the built in circuit for a constant current drive... though I have absolutely no basing on it, I've never tried it myself. I do however confidently believe what's already in there will not be enough to drive the 488.