Hi Yanxin,

Excellent work my friend, you are certainly making good progress on this project. 

Tweakie.

Hi Tweakie,

I learned a lot from you guys(you, Dave,Jeff,etc.), I have to admit that I love laser more than spindle , Less noise and more fun!
I generated a gcode file off a small image(our lovely Drew, downloaded from google), sharpened and converted to 8bit gray scale using IrFanView, then fed into BMP2CNC(sounds like no one has tried this for laser yet) and generated the gcode. The file size is 10cmx15cm, consists a total of 70k lines, the max depth is set to 0.0253", 0.0001" per step, tool tip size is 0.007" and line spacing is 0.007" too. Have not tried to burn it yet, may just work right out of the box , will try it soon and report back once get a chance.

Tweakie,
Nice job, as is always the case with your work.  I don't know much about ceramics, but wondering if burning an image before firing in a kiln would allow lower power to be used - ala laser diodes  .   I have some old greenware (?) left by the previous owner of my weekend home that I didn't want to throw away, so it looks like another experiment has now been added to my list.


Yanxin,
Nice work indeed.  It looks like your DAC is similar to what a couple of us are also using, just with a different IC.  If you haven't already, please join our group at: http://hobbycncart.com/forum/63-151-29.

Regards All,
John Champlain

John, thanks for your kind words, I am getting closer:)
Yes, I am using Dave's DAC circuit, it's simple and I can get 8bit 0~5V output. I have to say I am surprised by soldering skills while building those circuits, I have soldered 4 tiny cop-8 chips without any problems. 
Just checked your forum, sounds like another great place having fun, will register soon.

Yanxin

Yanxin,
Dave's circuit works slick, but you will lose the lower bits of output because of the threshold requirements of laser diodes.  I added a second op-amp to the output from the DAC so I could set a bias of about .2(?) volts minimum.  This lets me have the complete 256 bits usable over the full range of the 0v to 5v signal.  I typically modulate my diode between .3 amps min. and 1.6 amps max.  I'm not sure if I could go higher or not - don't want to risk blowing another diode.  I have a 0 to 2 amp meter hard wired in the leads to my diode so I can monitor its current draw.

Hope this helps,
John Champlain

Hi John,

I am curious, can you actually see the difference of a few bits? I actually was playing with the above mentioned IrFanView (which is a great program, by the way, thank you) and I could see no difference at all between depth of field 256 and 100. Actually, somewhere at 20I already struggled to see the difference. Either this program implies some other units or I am testing on wrong photos. Otherwise I can't tell any difference.

Dan

Yanxin,
Dave's circuit works slick, but you will lose the lower bits of output because of the threshold requirements of laser diodes.  I added a second op-amp to the output from the DAC so I could set a bias of about .2(?) volts minimum.  This lets me have the complete 256 bits usable over the full range of the 0v to 5v signal.  I typically modulate my diode between .3 amps min. and 1.6 amps max.  I'm not sure if I could go higher or not - don't want to risk blowing another diode.  I have a 0 to 2 amp meter hard wired in the leads to my diode so I can monitor its current draw.

Hope this helps,
John Champlain

John, thanks so much for your suggestions, will try that later. The driver board I built has a bias pot too, I have set it to 0.16a(probably should set a little higher) minimum for my M140 diode, would that have the same effect of adding a second op amp at DAC side? The max current I am getting from the driver is around 1.55a, very similar to yours, increasing the bias current will increase the  max current too.

- Yanxin

Hi Dan,
Losing a few bits from the bottom of a 256 bit image is not the same as reducing total bit depth of an image.  To me, my images were burning darker with the lower bits missing, but YMMV.  When I was able to use the full 256 bits, my results seemed to improve, hence my recommendation.  In truth, image engraving with analog modulation of laser diodes is still evolving, and we are all learning new things frequently.

Yanxin,
If you increment (jog) your diode control by one step at a time until your diode current starts to increase from your set minimum, this will tell you how may bits (if any) are being 'lost'.  Your driver may respond differently than mine, and you may not need the full 0 to 5 volt signal to get good results.

More here about my circuit (message #320): http://hobbycncart.com/forum/63-151-16

Best Regards,
John Champlain

Hi Dan,
Losing a few bits from the bottom of a 256 bit image is not the same as reducing total bit depth of an image.  To me, my images were burning darker with the lower bits missing, but YMMV.  When I was able to use the full 256 bits, my results seemed to improve, hence my recommendation.  In truth, image engraving with analog modulation of laser diodes is still evolving, and we are all learning new things frequently.

Yanxin,
If you increment (jog) your diode control by one step at a time until your diode current starts to increase from your set minimum, this will tell you how may bits (if any) are being 'lost'.  Your driver may respond differently than mine, and you may not need the full 0 to 5 volt signal to get good results.

More here about my circuit (message #320): http://hobbycncart.com/forum/63-151-16

Best Regards,
John Champlain

Thanks John, now I understand. I was assuming the current will start to increase based off the bias current at 1st step, looks like it's not, steps will be lost, I will prove that later.

I burned my first MDF today, no practice at all, first laser burned wood in my life, very excited, not good quality but at least it proves my DAC,driver and diode works as expected, and shades look good. See below pictures, burned too dark, and lines not merged(need to de-focus laser?), and possible backlash.

Yanxin

Hi John,

Thanks. I think I see what you mean.

Dan

My congratulations Yanxin, this looks like you are well on your way to producing some stunning images.  

A really excellent job my friend.  

Tweakie.

Yanxin,

Yes to Tweakie's comment - a really excellent beginning.  MDF burns dark, but your image shows very good image tonality.

The lines are something I also have a problem with.  Are you using 1/4-20 (or similar) lead screws?   That's what I believe is causing the lines, and I have just started building a small belt-drive machine to see if I can eliminate them.  Our friends who use ball screws don't have the lines.

John Champlain