LASER pulsing control

Hi Folks,

I bought a laser and driver combo online. It's a 405nm,150-200mw,6v laser module like in the picture below:

I'm now trying to pulse the laser using step/dir signals originally meant for a for a stepper motor. I've written some code that will make an arduino uno wait for those 2 signals, and once the 'step' and 'direction' pins are both high, the arduino will fire an output pin that will serve as a signal to 'fire the lazer'. That output pin is assigned to pin 13 so that the SMD led on the board will also light up and serve as an indicator for me to confirm that the code is working.

Here's the catch: So I run my program without the laser attached to the firing pin. The LED on pin 13 flickers, and I know that it's signalling correctly. However, when I plug in the laser, the LED doesn't light up at all, and nothing comes out of the laser.

Here's what I'm thinking:

1 the output pin 13 doesn't push enough current or voltage to drive the laser. (can someone please confirm this?) So I'm thinking of using a transistor to handle it, and source the power from outside the arduino. Would someone please recommend what part I can buy to fire it properly?

2 I also contacted the manufacturer, and learned that the circuit (in the picture) is not built for pulsing, but rather for continuous current. I need it to pulse.. so the question is can I insert the transistor (from #1) after the driver circuit to control the firing?

Thanks in advanced!!

The picture isn’t showing-up. Do you have a link to the specs or datasheet?

#1 the output pin 13 doesn’t push enough current or voltage to drive the laser. (can someone please confirm this?) So I’m thinking of using a transistor to handle it, and source the power from outside the arduino. Would someone please recommend what part I can buy to fire it properly?

Right… You’ll need a transistor or MOSFT. The I/O pins cannot directly power the LASER. You’ve also only got 5V whereas LASER is rated at 6V and that could also be an issue.

#2 I also contacted the manufacturer, and learned that the circuit (in the picture) is not built for pulsing, but rather for continuous current. I need it to pulse… so the question is can I insert the transistor (from #1) after the driver circuit to control the firing?

Maybe… It depends on the driver circuit. Normally, you’d design the driver from the beginning to be switchable/pulsable if that’s what you need.

An “extra” transistor can mess-up a good constant current driver because the driver is trying to supply continuous constant current while you’re trying to turn the current (and voltage) off.

If there’s just a simple current limiting resistor (like you use with an LED) or a “simple” constant-current circuit it should work fine.[/quote]

Semiconductor lasers must be driven constant current or they will be destroyed, they operate very close to the limit usually, so ensure the heatsinking is adequate too.

Without any details of the module can't say if it already has a constant current drive built in.

Constant current circuits can be modulated without any worries, just switch the entire circuit on and off with a MOSFET.

If its a switch-mode constant current supply there will be a limit to how fast you can switch it on and off, if an analog constant current circuit or series resistor, you'll probably get towards MHz rates.

Or get a 'TTL Modulated' Driver.

For information on driving lasers then I find this web page to be very good:- http://www.repairfaq.org/sam/laserdps.htm

405nm is probably not a diode pumped. most likely a discrete diode.