Need help with laser driver and TTL signal


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Thread: Need help with laser driver and TTL signal

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    Default Need help with laser driver and TTL signal

    I am trying to attach a laser diode to my CNC running MACH3. I purchased this driver to use with a 1w laser.
    Need help with laser driver and TTL signal-picture1-jpg

    I have configured MACH3 so that I can use M3 and M5 commands to turn off and on and use pin 17 for + and 25 for -. Confirmed with meter that I get 5V when on an ~0 when off. I can hook up a small 5mW laser to these pins and control on/off as well as use the spindle command to control the intensity. That part works. When I hook up the pins to the TTL connector on the driver board, power it, and use the same commands the voltage at the laser connector doesn't change regardless of how much I initially trim the voltage pot. It stays on all the time. I was hoping that I could turn off and on the laser with this setup.

    Any ideas?

    Thanks

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    Default Re: Need help with laser driver and TTL signal

    Laser diodes, like any other type of diode, do nothing until they hit a particular voltage and then (like a switch) they open up the floodgate and go very low impedance. So when the thing is on, regardless of power, you won't see a great deal of variation of the diode voltage. And, to a large extent, it's irrelevant.

    What you want to be measuring is the current, which means hooking up your meter (be sure to make sure the meter's in the right mode with the probes in the right sockets) in series with the diode instead of across it and measuring that.

    Also, these cheapo drivers seem to come in three flavours:
    - TTL (can't modulate output power with these, they're either on or off)
    - PWM (modulate with a PWM output from MACH3 and your BOB, it's a digital 0-5V square wave where the duty cycle of each pulse determines the value of the output).
    - Analog 0-5 or 0-10V where a steady voltage controls the output power.

    I bought my diode with a TTL driver under some illusion that I'd be able to run PWM control through it but, as soon as the power went up over about 1%, it just started flickering on and off. Useless. Replaced it with a proper PWM driver and moved onto the next issue - my particular BOB doesn't have any PWM support. Lol. Next step, I have a UCCNC UC400ETH controller sitting on my desk with a breakout board for it on the way. When that gets here I'll switch over and hopefully get control of both my spindle (analog) and laser (PWM).



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    Default Re: Need help with laser driver and TTL signal

    Thanks for the reply. Was hoping to use this as a PWM with Mach3 but would even settle for on/off. Seems to be on all the time whether or not TTL voltage is 0 or 5.



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    Default Re: Need help with laser driver and TTL signal

    You shouldn't need two pins for it, one either at 5 or 0 from the BOB and the other connected to BOB ground should suffice. My TTL board had a pullup on it, so that if the TTL input wasn't connected it defaulted to "on" state.



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    Default Re: Need help with laser driver and TTL signal

    On the Mach3 side those M commands are too slow to do anything practical. The delay will cause burning at the ends of the cuts. Check my past posts.


    Sent from my iPhone using Tapatalk



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    Default Re: Need help with laser driver and TTL signal

    One step at a time, I thought

    But Dean448 is right. Once you've got on/off control you're going to want to get rid of the M3/M5 and replace them with M11 (on) and M10 (off) to get rid of pauses.



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    Default Re: Need help with laser driver and TTL signal

    Thanks. I've been following the issues with M3/M5. As soon as I can on/off that's my next step. Hopefully a lot easier.



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    Default Re: Need help with laser driver and TTL signal

    I had the same issue... I had a ground loop due to connecting the diodes housing to the frame...


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    Still Learning..... :D


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    Default Re: Need help with laser driver and TTL signal

    Quote Originally Posted by Bx3mE View Post
    I had the same issue... I had a ground loop due to connecting the diodes housing to the frame...


    Sent from my iPhone using Tapatalk
    What was the fix? Working now?



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    Default Re: Need help with laser driver and TTL signal

    Fix is most likely to ground the frame properly. I know on mine (OmioCNC) they, for some reason, decided to keep everything isolated. Frame isn't grounded. Spindle isn't grounded, nor is the VFD, nor are the stepper drives and the USB BOB is floating too - sitting on rubber spacers and an insulated sleeve around the USB socket so it doesn't ground on the case! Horrible, horrible electrics which caused some real weird problems. Fixed 'em by wiring the machine frame to mains ground but one day I will need to go through and properly star point ground the whole lot.



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    Default Re: Need help with laser driver and TTL signal

    Yes working now... Heat dissipation fr.o.m. Dioderna goes via housing so everything in contact with it or its cooling finns bill be conducting diode psu - voltage. This causes pwm or other signal to likely drop voltage making the signal invisible to the recieving circuit. Fix can be adding optocoupler or isolate the diode/housing. I used 3D printed holder and plastic screws.


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    Default Re: Need help with laser driver and TTL signal

    Try to just make a bench test placing the diode with housing on some isolated material to see if this might bee the issue...


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    Still Learning..... :D


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Need help with laser driver and TTL signal

Need help with laser driver and TTL signal