Author Topic: PWM on Banggood laser with L7  (Read 2016 times)

aerosaur

  • Newbie
  • *
  • Posts: 2
    • View Profile
PWM on Banggood laser with L7
« on: February 03, 2017, 07:11:41 AM »
Hello good people,

I recently bought this machine http://www.banggood.com/2500mW-A3-30x40cm-Desktop-DIY-Violet-Laser-Engraver-Picture-CNC-Printer-Assembling-Kits-p-1003863.html and have been getting familiar with firmware, software, fixing wobbly lines etc. Found this forum invaluable, so thanks to everyone!

Naturally, I've been trying to get PWM to work. I'd just like confirmation - from what I've read here, even if I set the jumper on the L7 board under the nano to v0.9 and install suitable firmware (I've been using GRBL 1.1e installed via T2Laser), I may not get greyscale due to limitations of the laser module itself. In my experience, trying to engrave the T2Laser greyscale chart, it only turns on over over 80% power, with no discernible difference in burn.

If I want greyscale, should I be buying a laser such as this one http://www.banggood.com/450nm-3500mW-3_5W-Blue-Laser-Module-With-TTL-Modulation-for-DIY-Laser-Cutter-Engraver-p-1103261.html that has a TTL board? Unfortunately I don't see a board capable of 2.5W sold individually right now.

Zax

  • T2Laser
  • Global Moderator
  • Hero Member
  • *****
  • Posts: 6244
    • View Profile
    • T2Laser
Re: PWM on Banggood laser with L7
« Reply #1 on: February 03, 2017, 08:07:13 AM »
If you want to control the laser power precisely then yes, you need a TTL laser.

The L7 board will drive these just fine, you don't need to replace it. The newer board Eleks Mana SE has the PWM/TTL signal on the laser connector which is nice but not necessary (just use my trick in message below).

http://benboxlaser.us/index.php/topic,402.msg6591.html#msg6591
http://benboxlaser.us/index.php/topic,1262.msg15518.html#msg15518

The one you posted or this is the newer kind with the integrated driver:
http://www.banggood.com/445nm-2_3W-2300mW-Blue-Laser-Module-With-Heatsink-For-DIY-Laser-Cutter-Engraver-p-1105563.html

If you just want greyscale, save your money and use velocity mode. It takes a little more effort to setup (use the rapid feed rate for white and feed rate for black) but it works great and only requires on/off from the laser. It's also faster, so it's a win-win. You can use this same method with DXF colors to feed rates for cutting too.

ggallant571

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 2407
    • View Profile
Re: PWM on Banggood laser with L7
« Reply #2 on: February 03, 2017, 08:33:57 AM »
For my information, why is TTL more precise that the MOSFET? The TTL boards need to switch the 12V.
SARCASM - Just one more service we offer here.

wild.bill

  • Sr. Member
  • ****
  • Posts: 492
  • Hey Laser Lips, Your mother was a snowblower
    • View Profile
Re: PWM on Banggood laser with L7
« Reply #3 on: February 03, 2017, 08:49:04 AM »
For my information, why is TTL more precise that the MOSFET? The TTL boards need to switch the 12V.

The non TTL laser has only a 12 Volt line going to it and the power to the laser is switched on and off to get the power level that is wanted. All of the power to the laser is switching which is why the MOSFET is needed.

With the TTL laser there are two sets of wires going to the laser (they sometimes share the ground to make it 3 wires). On set is 12 volts which is always on. You will notice that with a TTL laser the Fan is ALWAYS on because the 12 volts is always on. Then the diode is switched via the 5 volt TTL line. Very little power is actually going through the wire - its just to control a circuit - not power the laser.

By not switching the power you can get more accurate control.
Laser: was an A3 2.0w TTL L6 Z axis now 2'x3'
          OpenBuilds ACRO 510 w/ 2.0W TTL laser Cohesion Mini Z axis Homing switches
          K40 Cohesion Mini 60W LightObject LPS
          80W Red-Black 500x700

cool is simply a subjective state of mind

Zax

  • T2Laser
  • Global Moderator
  • Hero Member
  • *****
  • Posts: 6244
    • View Profile
    • T2Laser
Re: PWM on Banggood laser with L7
« Reply #4 on: February 03, 2017, 08:53:09 AM »
Using the MOSFET is switching the 12V to the constant current driver, some drivers use a soft start so the response may not be linear (it won't switch fast enough to support lower PWM). A true TTL driver is designed to switch quickly and uses the input within the circuit to control the output.

aerosaur

  • Newbie
  • *
  • Posts: 2
    • View Profile
Re: PWM on Banggood laser with L7
« Reply #5 on: February 03, 2017, 01:51:08 PM »
Thanks for the advice, I certainly shall test results with varying the laser speed, and keep upgrades in mind.

ggallant571

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 2407
    • View Profile
Re: PWM on Banggood laser with L7
« Reply #6 on: February 03, 2017, 02:00:13 PM »
"A true TTL driver" from a Chinese retailer seems like an oxymoron. That would imply specifications and user guides.
 
SARCASM - Just one more service we offer here.

Hippie With A Cowboy Hat

  • Full Member
  • ***
  • Posts: 142
    • View Profile
Re: PWM on Banggood laser with L7
« Reply #7 on: February 03, 2017, 08:33:25 PM »
"A true TTL driver" from a Chinese retailer seems like an oxymoron. That would imply specifications and user guides.

LMAO  ;)
Am I the only one who can't sleep, wondering why John Wayne walked that way?