Laser cutter, part IV

[bodger]

Now that I have the EiBot board running the steppers, I'd like to have it turn the laser on and off too. Normally, the Egg-Bot this board was designed for has a servo to raise and lower the pen. This is controlled with a pulse width modulation (PWM) output. But I needed an on/off signal to feed to the laser. Looking at the documentation, I noticed references to a solenoid output, which sounded like just what I needed. Looking at the earlier versions, I could see the circuitry to drive the solenoid, but that circuitry isn't present on the board I have. Looking at the schematics, the I/O pin that drives it is now used for another purpose. I downloaded the firmware source code and tried to dope out what the current code did, but I wasn't able to figure it out. So I sent a note to the designer and asked him about it. He sent back a prompt and helpful reply, stating that the RB4 output should have the solenoid signal. I soldered a header on the appropriate pins and hooked up an LED (and current limiting resistor). At first, I had the LED hooked from +5V to RB4, but that voltage isn't supplied by the board when it's running from just USB, so no joy. So I hooked the LED between RB4 and ground, and sure enough, it followed the pen up/pen down state.

So I grabbed a handy male-female jumper wire and plugged the female end onto the RB4 post (lower left), and ran the male end into the TTL "L" input on the laser power supply (upper right). I fired up InkScape with the Egg-Bot extensions, and exercised the pen up/pen down command. Sure enough, it controlled the laser, but with inverted sense. Happily, the laser power supply also has a TTL "H" input, so I ran the lead to it instead. This is convenient, as the manual button can use the "L" input and the EiBot board can control the "H" input, and I don't have to wire-or anything. Testing showed that the EiBot board now turned the laser on for "pen down" and off for "pen up", just what I wanted.

I played with the Egg-Bot extensions (they're very configurable) some to match the laser cutter better, used the "polygon/star" function in InkScape to draw a simple star, placed a scrap of acrylic in it (thanks for the suggestion, graysoul), pressed the "laser enable" button, and told it to plot.

Comments

Great series on your laser experiences!

[mcclmark.myopenid.com]

Could you provide the model number and the ebay seller you purchased this from?

How many watt laser? What has been your experience with materials -can you cut 1/4” acrylic? ABS? Have you been able to cut mylar PCB stencils (enough resolution)?

Keep the great posts going!!!

Re: Great series on your laser experiences!

[bodger]

Oh, I plan to. I'm currently adding air assist, which turns out to be more involved than I expected, as the new optical head is longer and has a different mount. I'm also working on using the limit sensors for an auto-home functionality. I'm working on using it to cut and engrave new
graticules for Tektronix 500 series scopes.

[bodger]

It's a Shenhui K40III. I got it from eBay seller love-happyshopping
(goofy name, they're BaiAoran in real life). It's a 40
watt laser. I haven't been able to cut 1/4" acrylic all the way through, but I expect to be able to when I get the cutting platform height adjusted. If not, I'll add air assist, which is a big help for thicker material. I'll admit I haven't tried mylar stencils yet, but I think the steppers will have sufficient resolution (especially with the EiBot board's microstepping). It remains to be seen if the mechanics will need adjusting for sufficient accuracy.

we want more!

[mcclmark.myopenid.com]

I'm looking forward to more posts on your laser experiences :)