PWM voltage reduces

[Athul]

HI,

    I was previously running with GRBL and got full laser power at 5V and I recently shifted to smoothie but the power was kinda lower the before. So yesterday I checked the voltage between IN and GND and noticed a 3.6 V instead of 5V for S1 command. after a lot of checking I found that if I disconnect WP from ground I will get 4.98V at IN and voltage reduce to 3.6V when WP connected to GND. I"m sending PWM and active low signal through a bi-directional TTL , and tried to power the HV side(5V side) of TTL from seperate power supply, but result was same. Anyone have any idea what causing it??

Anybody checked there PWM volatge at IN terminal??

I'm attaching my connection diagram.

Thanks

[Athul]

sorry not bi-directional TTL but bi-directional LLC

[Athul]

Can anyone give me the connection diagram for logic level converter, please

[Athul]

[ajf]

Have you seen this one?

[Athul]

@ajf

Do you have any idea about my issue.

With WP and Tl connected to ground I'm only getting around 3.7V at the IN terminal for S1 command. I checked the voltage at the input side, It's 3.3 V but output is only 3.7

[ajf]

You're using Smoothie if I recall, could you attach (not paste) your config file. 

[Athul]

@ajf

For S1 command, i'm getting 3.3V at the LV side of LLc(input pwm), but at HV side(output pwm) it's not 5V but 4.04V.

Then I removed the connection from IN, then it showed 4.98V

Looks like when it get connected to IN , voltage reduces from 4.98V to 4.04.

I tried to explain my best with attached pictures. Please take a look.

Also can you verify my LLC connection, Is it right?

[ajf]

Sorry for the late reply.

The level shifter is wired up correctly as far as I can tell.  I don't think measuring the voltage on the IN tells you anything, it's PWM'd. I'd say rely on the ammeter on your machine to see if you are getting the intensity your setting in gcode.

[Athul]

I don't have a ammeter in my machine.

But if the PWM is 100% duty cycle it should show 5V on multimeter, right?

Also I got a message asking
"Why do you have # in front of this in config?

#laser_module_pwm_period 20 # this sets the pwm frequency as the period in microseconds "

In smoothie documentation for laser cutter doesn't say about that. Is it necessary to remove # ?

If the PWM is with 100% duty cycle it should show 5V in multimeter, right?

Can you give me your laser PSU manual or a link if possible?
I wanna know how much current your 5 V terminal can give, mine says 20ma. Isn't that enough?
I have explained my problem in detail in sparkfun forum, please take a look.

https://forum.sparkfun.com/viewtopic.php?f=14&t=43924

[Jason Barnett]

Athul,

 I didn't see any mention of it having been tried, so here's my suggestion.

Try uncommenting the following line.

laser_module_maximum_power                   1.0             # this is the maximum duty cycle that will be applied to the laser

I don't know what the default value is, but if it were "0.8" instead of "1.0" that would explain the problem you are seeing.

Hope this helps,

Jason

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[Athul]

I figured out what's the problem.

10K pull up resistor on the HV side of logic level converter was too large in my case. I figured this out by doing,

1. connected 5V to IN terminal by a wire , measured voltage across it. Got 4.95 on DMM.

2. Connected 10K between IN and 5V got 3.7V if TL is not grounded and 4.04 when grounded. What I need is 5V when TL is LOW.

3. Connected 1K between in 5V and IN , got 4.8V at both TL disconnected from GND and at TL is LOW

I think this is due to the high input impedance of IN terminal 

So replaced 10K with 1k in logic level converter and I'm getting around 4.8V for S1(100% duty cycle)

@Jason

By default

 laser_module_maximum_power 0.8 # this is the maximum duty cycle that will be applied to the lase

I think this is valid when a command without S value is sent to the machine like M3 G1 X100 F400 M5, so machine will run at the power specified in that line.

But for M3 G1 X100 F400 S1 M5 machiine will give full laser power(3.3V PWM with 100% duty cycle.

Anyway thanks for the reply :)

I also have a doubt . Below is the laser configuration file from smoothieware laser cutter guide.

http://smoothieware.org/laser-cutter-guide#toc13

 I saw some other configuration with # removed from all lines. Is that necessary(Mine is like this with a laser fire switch module)

https://gist.github.com/ajfoul/b32a0432f337e81f3ab6

# Laser module configuration
laser_module_enable                          true             # Whether to activate the laser module at all. All configuration is 
                                                              # ignored if false.
laser_module_pin                             2.5              # this pin will be PWMed to control the laser. Only P2.0 - P2.5 
                                                              # can be used since laser requires hardware PWM
#laser_module_max_power                       0.8             # this is the maximum duty cycle that will be applied to the laser
#laser_module_tickle_power                    0.0             # this duty cycle will be used for travel moves to keep the laser 
                                                              # active without actually burning
#laser_module_pwm_period                      20              # this sets the pwm frequency as the period in microseconds

[Athul]

Sorry, my mistake

laser_module_maximum_power 1.0 # this is the maximum duty cycle that will be applied to the laser

This line specifies the maximum power

#laser_module_default_power                   0.8             # This is the default laser power that will be used for cuts if a power has not been specified.  The value is a scale between

                                                              # the maximum and minimum power levels specified above

This line specifies the laser power when S parameter is not specified

Below is my laser configuration

Should I remove # from all lines

## Laser module configuration

laser_module_enable                          true            # Whether to activate the laser module at all. All configuration is

                                                              # ignored if false.

laser_module_pin                             2.3             # this pin will be PWMed to control the laser. Only P2.0 - P2.5, P1.18, P1.20, P1.21, P1.23, P1.24, P1.26, P3.25, P3.26

                                                              # can be used since laser requires hardware PWM

#laser_module_maximum_power                   1.0             # this is the maximum duty cycle that will be applied to the laser

#laser_module_minimum_power                   0.0             # This is a value just below the minimum duty cycle that keeps the laser

                                                              # active without actually burning.

#laser_module_default_power                   0.8             # This is the default laser power that will be used for cuts if a power has not been specified.  The value is a scale between

                                                              # the maximum and minimum power levels specified above

#laser_module_pwm_period                      20              # this sets the pwm frequency as the period in microseconds

switch.laserfire.enable                      true             #

switch.laserfire.output_pin                  1.31!^           # connect to laser PSU fire (!^ if to active low, !v if to active high)

switch.laserfire.output_type                 digital          #

switch.laserfire.input_on_command            M3               # fire laser

switch.laserfire.input_off_command           M5               # laser off

Follwing is the configuration from smoothieware laser cutter guide