Chinese laser module on ramps, engraving questions

I recently got hold of a chinese 2.5 watt laser (like this one: [www.ebay.co.uk]) and I'm running it with Marlin Kimbra on a arduino mega with ramps board. The laser's TTL input is connected to D44 on the ramps, including a 10K (or so) resistor to ground so the laser doesn't turn on on boot. Fan PWM has been set to pin 44 instead of D9 in the firmware. Cutting goes very well, but Im having trouble with raster engraving. Gcode commands like M106 Sxxx should give me variable output, but it does not seem to work; it just output black lines. It looks like the TTL input just switches the laser on and off although a single command (like M106 S10) through pronterface seems to work.
The laser driver also has an analogue input.
Anyway, Im wondering what I'm doing wrong.
Should the TTL input be used for switching on and off and should the analogue input be used for variable laser power? Or should a power output of the ramps (like D9) be used to power the laser driver. Should I use a specific PWM frequency? Another pin? (servo)
Anyone has any experience with this?
Should I invest in a decent driver circuit?

Edited 2 time(s). Last edit at 07/20/2017 03:57AM by finch666.

I had to decrease the laser current a lot to be able to engrave grayscale with a PWM signal ( 2W blue laser )
If you get burned traces where there should be no trace, then the TTL input is over-sensitive. A voltage divider would help.
The analog input is often laid out for 0-10V, so you'd get only 50% power from a 5V pin. But its worth a try.

Edited 1 time(s). Last edit at 07/21/2017 04:20AM by o_lampe.

Thanks for your reply, o_lampe!
You must be right. Today I ran tests with the PWM on max 10, max 16 and max 20 and even on max 10 I got fully burned traces.
Will try a voltage divider tomorrow
The analogue input appears to be high on boot, causing the laser to fire unwanted....

Edited 1 time(s). Last edit at 07/21/2017 03:36PM by finch666.

Ran a test yesterday with voltage on the analogue input.
At 2 Volt the laser is not burning anything, but gives me the opportunity to focus it right.
But at 5 V is seems to be almost on full power.
Laser power seems to be not lineair with the voltage. I suspect the driver now not being capable of giving the laser the right power, and being too slow to keep up with the PWM changes. Will try another driver board.
Was thinking about adding an rc filter to the pwm output of the ramps board, but my guess is that won't work.....

Edited 1 time(s). Last edit at 07/23/2017 12:39AM by finch666.

I started testing my laser driver board with a common high power LED ( Cree 3W ) and a multimeter to control current.
That way, you can see whats going on without the risk of loosing your eyesight.

I don't understand voltage trials
The driver circuit is 12V input
use a separate 12V power supply with enough current (amps) capacity

This should provide max laser power at continuos ON

Then TTL between 0 -5 volts to PWM the ON/OFF cycle (should keep it below 5kHz)

fan output is not TTL but just a 0 -12 volt for fan drive

Look for a TTL output on arduino
Look at the pins file for pin definition

[reprap.org]

What choices in your software is there to control laser?

... the cheap chinese drivers are not consistent in behaviour and quality, even if in same layout/form and from the same vendor - so not really worth to compare to a standard like "TTL" or a common 0-5V or 0-10V analogue input

Even with most comercial drivers analogue controlling is mostly not linear and has to be adjusted for the specific diode and the resulting (effective) power in relation to speed.

I'm driving all my laser-engravers and -cutters with pulsed drivers, where the resulting power is a result of pulse length and count of pulses per mm, not plain PWM.

One essential thing to look at - only use max. 95percent of the stated "safe" current with good cooling, or the diode will degrade with time ... and check the driver for eventual spikes or transients when pulsing, as this will sure kill your diode pretty fast ...

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Quote
finch666

The laser driver also has an analogue input.
Anyway, Im wondering what I'm doing wrong.
Should the TTL input be used for switching on and off and should the analogue input be used for variable laser power?

Are you sure the driver has an analogue input? It is not advertised and I can't identify it on the product images ...

I guess, it is just a simple TTL driver - i.e. you connect laser power (12V) to LD+/- and use the TTL input to connect your controller's PWM port. A "high" signal (~5V) will power the laser, a "low" signal (~0V) will switch it off. The right combination of PWM pulses and movement speed could give you the ability to run engravings with less intensity. Eventually you could use the potentiometers to reduce the laser current if you don't need the full power.

Edited 1 time(s). Last edit at 07/24/2017 04:50AM by trapperjohn.

Quote
cozmicray
I don't understand voltage trials
The driver circuit is 12V input
use a separate 12V power supply with enough current (amps) capacity

This should provide max laser power at continuos ON

Then TTL between 0 -5 volts to PWM the ON/OFF cycle (should keep it below 5kHz)

fan output is not TTL but just a 0 -12 volt for fan drive

Look for a TTL output on arduino
Look at the pins file for pin definition

[reprap.org]

What choices in your software is there to control laser?

Driver had analogue input too, so I hooked up another adjustable power supply to the analogue input.

In Marlin I used the declared FAN_PIN and assigned it to pin 44 for PWM, instead op assigning it to one of the MOSFET's output.
PWM has been set to 50kHz. Should that be lowered?

Quote
VDX
... the cheap chinese drivers are not consistent in behaviour and quality, even if in same layout/form and from the same vendor - so not really worth to compare to a standard like "TTL" or a common 0-5V or 0-10V analogue input

Even with most comercial drivers analogue controlling is mostly not linear and has to be adjusted for the specific diode and the resulting (effective) power in relation to speed.

I'm driving all my laser-engravers and -cutters with pulsed drivers, where the resulting power is a result of pulse length and count of pulses per mm, not plain PWM.

One essential thing to look at - only use max. 95percent of the stated "safe" current with good cooling, or the diode will degrade with time ... and check the driver for eventual spikes or transients when pulsing, as this will sure kill your diode pretty fast ...

Then it looks like my driver indeed has a very small window to effectively regulate the power. Guess it's better to settle for line engraving and cutting for the time being and forget about raster engraving

And no oscilloscope available, so I'll just have to see how it holds

Quote
trapperjohn

Quote
finch666

The laser driver also has an analogue input.
Anyway, Im wondering what I'm doing wrong.
Should the TTL input be used for switching on and off and should the analogue input be used for variable laser power?

Are you sure the driver has an analogue input? It is not advertised and I can't identify it on the product images ...

I guess, it is just a simple TTL driver - i.e. you connect laser power (12V) to LD+/- and use the TTL input to connect your controller's PWM port. A "high" signal (~5V) will power the laser, a "low" signal (~0V) will switch it off. The right combination of PWM pulses and movement speed could give you the ability to run engravings with less intensity. Eventually you could use the potentiometers to reduce the laser current if you don't need the full power.

CN2 is TTL input, CN3 analogue; it says so on the PCB...... Anyway, it appears the driver isn't that sophisticated and offers very little room for regulation of the laser power, both PWM and analogue.....