PPM vs. PWM for laser control
Posted by chromvis
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PPM vs. PWM for laser control March 13, 2018 04:08PM |
Registered: 7 years ago Posts: 7 |
I encounter the problem using Marlin Kimbra version for K40 machine. I noticed significant loss of laser power. When I checked with oscilloscope it appears that my pin 6 (standard for laser PWM control) actually has PPM version of signal (pulse position modulation, 2 ms pulses with 20 ms period suitable for hobby servo control). Actually, pins 4, 5, 6, and 11 are dedicated for servo control on pololu shield. I tried standard Marlin and got the same. With this type of a signal you get max 10% of laser power. Any idea on how to change it.
I install Smoothieboard, which works fine except that if I want to do raster engraving it could not do it correctly, so I want to go back to Ramps 1.4 but need to solve this problem.
Any suggestions are highly appreciated.
I install Smoothieboard, which works fine except that if I want to do raster engraving it could not do it correctly, so I want to go back to Ramps 1.4 but need to solve this problem.
Any suggestions are highly appreciated.
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Re: PPM vs. PWM for laser control March 13, 2018 05:13PM |
Admin Registered: 16 years ago Posts: 13,886 |
... you can insert a mono-flop chip with a trimpot to adjust the pulse-length - e.g. a NE555 in a standard monoflop circuit ...
Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]
Call for the project "garbage-free seas" - [reprap.org]
Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]
Call for the project "garbage-free seas" - [reprap.org]
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Re: PPM vs. PWM for laser control March 14, 2018 12:10AM |
Registered: 7 years ago Posts: 7 |
Not sure that it is an optimal solution. I searched today and find that even the author of #servo library for Arduino does not know how to switch back from PPM to PWM. Apparently, servo.detach() does not work, although it should according to Arduino manual.
I actually simply comment the call for #servo library in base.h file of MK firmware. The compilation went fine but I did not check with hardware attached yet.
I am a bit surprised that no one notice it here. It appears to be well known problem in Arduino community, at least it is my impression from today extensive search.
I actually simply comment the call for #servo library in base.h file of MK firmware. The compilation went fine but I did not check with hardware attached yet.
I am a bit surprised that no one notice it here. It appears to be well known problem in Arduino community, at least it is my impression from today extensive search.
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Re: PPM vs. PWM for laser control March 14, 2018 04:06AM |
Admin Registered: 16 years ago Posts: 13,886 |
... I'm avoiding PWM with accelerated moves, as it would burn more on line starts and ends.
Better use the CLOCK pin of the extruder, as it's exactly giving "Pulses per millimeter".
I'm driving my (cartesian style) laser-engravers with an ArduinoDue as "slave" with a pulse length of 500ns -- and adjusting the engraving/cutting power by an Arduino pro mini inside the laser driver, by varying the pulse length between 5µs to 400µs ...
Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]
Call for the project "garbage-free seas" - [reprap.org]
Better use the CLOCK pin of the extruder, as it's exactly giving "Pulses per millimeter".
I'm driving my (cartesian style) laser-engravers with an ArduinoDue as "slave" with a pulse length of 500ns -- and adjusting the engraving/cutting power by an Arduino pro mini inside the laser driver, by varying the pulse length between 5µs to 400µs ...
Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]
Call for the project "garbage-free seas" - [reprap.org]
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