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Subject: Re: [Homebrew_PCBs] Re: laser ablation of paint on copper clad

From: Camillus <camillus_blockx@...>
Date: 2014-12-13

Hi, maybe you should consider double addressable ram, is a bit more expencive, but it can be written and read at the same time, ( has two address counters in it ), I'm not shure but they call it LIPO or something likethat. 
Anyway it is sure fast enough and wile your avr is pumping bits in it the cnc can read them. It depends now on what you need be the fastest.

cb

On 12/13/2014 11:06:25 AM, Slavko Kocjancic eslavko@... [Homebrew_PCBs] <homebrew_pcbs@yahoogroups.com> wrote:

On 13. 12. 2014 11:39, 'Tony Smith' ajsmith1968@...
[Homebrew_PCBs] wrote:
> At 1,000 DPI, the laser isn't going to be anywhere near it's supposed to be
> anyway. Close enough thought.
>
> The beam of the laser will be probably bigger than a dot a 1,000 DPI (which
> is good as the overlap fills in the gaps) depending on a bunch of things.
>
> Dunno how LinuxCNC does rastering, but often the laser is left on between
> dots so that evens things out. Sometimes you want dot - dot - dot lasering,
> but not in this case.
>
> Tony
>

The laser dot is just little under 1000dpi in size. But I have limited
on off timings so the width I can controll is about 700DPI. But this is
true only for rotation axis. I advance board for only 0.01mm each
revolution so there are plenty of overlap. And I do leave laser on if
there are more same dots in a row.

My preprocesor program just crunch the coordinates and make file stream
of '1' and '0' for laser for each 15us. The linuxcnc with component
'streamer' then stream this each 15us to the laser. And here is
bottleneck as I can't go faster (but I want) and I need to make some
special hardware to stream much faster than 15us/pulse.

I think to use some AVR with plenty of ram and to upload entire stream
on it, and after that just stream bits. At 1 bit per 1us the AVR will
work hard. But seems that static ram is just too small to fit entire
image, I will probably use dinamyc ram (4Mbits ∗4). As I calculated I
don't need to worry about refresh as cycling as streaming is fast
enought to keep memory refreshed. But need to cary refresh when data is
uploading and waiting start of operation where is enought time to proper
manage refresh cycle.



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