Hi all.
I have a problem. I have a laser ingraver, with arduino uno and cnc shield ver.3
I want to connect a laser modul, but the laser only have 2 core, black and red ( yes and 2 to the fan )
I meen i have to connect the laser direct on Z- or Z+, bur it not work
Offcause I have enabled the laser 
Do I have to connect on another way ?
// Lars Plovmann, DK
What laser module do you have and where on the shield are you connected?
Its a noname china laser, and only with 2 cores / wires. Like I write, I tryed Z+ / Z-, but not working 
Post pictures of your laser module and controller.
Show as much wiring as you can.
Z+ and Z- are the z axis pins. I believe you need to use the spin enable pin D12 on the shield. Also set $32=1 to set the arduino grbl in laser mode. The other question is if the laser module is just a laser diode or a laser power supply with a laser diode build in… if it is just a laser diode then you need a current source applicable to the laser diode. E.g. something that put out exact e.g. 1.6V with lots of current. Good luck!
Laser modules with only two wires doesn’t have a TTL/PWM signal input. Instead they just have power wires for the driver/diode. You need to provide power (mostly 12V from the provided power supply) to these wires, which is not available at the CNC Shield. This means you need additional electronics (MOSFET) to switch the 12V power for the laser with the spindle enable signal output from the CNC Shield.
Hint: If you use the spindle enable output, you will not be able to adjust the laser power. It will allways use maximum power! You would need to use spindle PWM output to be able to change the laser power, but a two wire module is not made for PWM modulation and will not work well with PWM modulated power.
Asking with interest,
What is the difference in a Laser Diode operation between:
Power modulated with 5vdc PWM; power on/off with 0v-12vdc on 12vdc power input
Power modulated with 12 power input cycled as 12V PWM; power on with 12V PWM value >0; power off with 12V PWM value=0.
Why wouldn’t modulating the 12 power directly work as well as 5V signal modulating the lasers 12v power internally?
If you cannot control power from the interface in a Laser module like this what are these modules good for?
A laser diode driver is basically a constant current power supply. Drivers with PWM input have a MOSFET at the output of the driver to switch the laser diode. I expect this to be faster than if the whole regulator has to power up/down with PWM frequency.
My first laser diode module was a two wire module and it kind of worked with PWM, but the result was much better when I replaced the driver with a TTL/PWM one.
You’re saying that the laser’s internal power supply does not have the switching response needed for PWM control.
Thanks that makes sense.