how to control laser with 3.34V parallel port

[StevoLaser]

Hi,

I have finished the build on my 48" x 24" 40w co2 laser. I am pleased with the motion control but not yet satisfied with how the laser fires.

Attached is a pic from a test lasing.

Initially, I was using pin 17 from the parallel port to turn on or turn off a relay. When the relay closes,"Gnd" and "L" on PSU are connected and the laser fires. When the relay opens, "L" and "Gnd" are no longer connected and laser stops firing. It "works" but there is a slight delay in the closing of the relay, so I am trying to figure out how to connect from my break out board to the Laser PSU without a relay

I tried connecting pin 17 directly to "L" . The laser would fire, but I could not make it stop firing.
Using a voltmeter from pin 17 to gnd I could get 3.34 volts or .14 volts depending on whether pin was active or not

I have tried several different alternatives. I enabled the Z axis using pins 6(step) and 7(dir). Using voltmeter I measured 3.34 volts or .14 volts from pin 7 to gnd.
I enabled the A axis using pins 8(step) and 9(dir) and measured 3.34 volts and .14 volts from pin 9 to gnd.

I can get the laser to fire with any of these, but not go off. Is it because my voltage is not 5v?

I was told that with Mach 3 it is best to use "a laser PSU which uses an ‘Active Low’ trigger input" which is why I have been aiming for the "L" on the PSU.

How can I connect my break out board directly to my PSU?
What am I doing wrong?

Thank you

Steve

[NickWL]

Very clever and a nice implementation of a fairly non-standard way of doing things!
I fear the delay, hysteresis and whatever else in the PIO-controlled relay system will prevent you from ever getting really sharp cuts (let alone engraving) so I recommend you bite the bullet, shell out for a Lightobjects 608 or 7x Digital Signal Processor (DSP) and get some really good control into what sounds like the makings of a great system.
Good luck!
Nick

[Masao]

I think the PSU is expecting 5V logic circuit. You will need to use level translator IC such as 74125 (Quad 3.3V to 5V level shifter) or make level shifter using transistor circuits that will convert your 3.3V logic level to 5V logic level.

74HCT125
https://www.adafruit.com/products/1787

[StevoLaser]

At some point "down the road" I am likely to buy a DSP. Currently I am using Mach3, in part because I have several cnc machines and I feel somewhat comfortable learning how to adapt the systems to different applications.

Honestly, I think the DSP is the way to go. At a glance, I couldn't tell what else I'd need to buy. I already have motors, a motion control card that is already getting step/dir signals and spitting them to the axes. If I get a DSP, would I need new motor drivers? I've got either 169 or 269 oz/in nema 23 steppers.. do I need to get new steppers?

For now, instead of a relay, I installed a transistor. Base is Pin 16 now, collector is "L" and Emitter is "Gnd" It seems to work pretty ok and I just cut a gear out of 1/8" acrylic:


I am sure the real "fun" will start when I try to engrave...

Thank you for the replies

Steve

[Tech_Marco]

Steve

You don't need new drivers or motors if you already have it. The output from the DSP can be either High or Low you pick. The DSP will give you an excellent performance on engraving and advanced features like PPI, cut out on cutting. Unlike Mach always having delay and troublesome speed feeding issue on laser, the DSP take care all

Marco