Moshi-to-laos-conversion-SH-K40-1V » History » Revision 3

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bullar, 2014-08-24 22:30
fine tuning


I bought my Chinese Laser Cutter from German vendor in 2014 in order get a Laser Class 1 system. A Class 1 laser is safe under all conditions of normal use. No need for any eye protection which increases the WAF (wife acceptance factor).
After some trials I faced the common issue with MoshiDraw and the corresponding controller (MS10105 V4.5). One of the severe drawbacks of V4.5 is the missing link between controller board and laser power control. The laser power has to be set manually for each job.
The next versions of the controller (V4.6) solves this bottleneck but it's still a closed system. And the Chinese MoshiDraw software is ugly...
My new objective was clear: I have to move to open source (LAOS). The following pages will describe the findings I had due to some differences in the actual machine version.

Differences to older posts

Laser Power

My laser cutter hosted a MY JG40W power supply with PWM power control input.
Laser PSU

I used the following connectors:
K- trigger button - to panel button
K+ trigger button + to panel button
G Ground to LAOS main controller (GND) and level shifter unit
IN PWM input, 0/5V, 0...100% duty cycle to LAOS main controller (Laser PWM) via level shifter unit
5V +5V output for level shifter unit only
24 +24V output n/c
G Ground to LAOS main controller (GND)
5V +5V output n/c
L Laser on to LAOS main controller (Laser On)

24V and 5V from this power supply are not used in my installation. There are separate PSUs available in order to keep the controller operating while the laser is powered off (laser class 1 safety issue).

Laser power controller

Here the actual system is much more modern and supports a digital power adjustment in 1/10, 1 and 10% steps (but still suffers from missing link to main control board).
The board is called 6C6879-LEDPAD-A. It was replaced by an I2C-Panel of LAOS

The new control panel

I added a LED showing the laser activity and a button to trigger the laser. The rest is supported by I2C-Panel. The front design file (SVG) is attached.
Control panel

Signal integrity issue

LAOS main board uses optocouplers for laser control (if you don't use the transistor output). In a lot of config files I found that PWM frequency is set to 1KHz.
In my system the frequency from power control panel was 21KHz. But this is a little fast for the optocouplers. The ground level get weak even with a pull-up of >470Ohm.
The picture shows the signal at optocoupler (reference in yellow is the transistor output w/o optocoupler).

PWM signal integrity

Therefore I decided to build a level shifter unit. With an op-amp (TLC271) the level at the optocoupler is judged at approx. 3V (with few 0.1V hysteresis). A following schmitt-trigger
(74LS14) drives the laser PSU directly. Power (+5V) for this circuitry is provided by the laser PSU in order not to jeopardize the isolation.

The level shifter soldered on a small PCB:

Level shifter unit

My Laser cutter after all modifications (until m/o Aug 2014)

Laser cutter (final)

Updated by bullar almost 10 years ago · 3 revisions