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Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062
Hi all.
Currently trying to get this pcb etcher working.
At the moment the main problem I am running into is the memory. The current setup was a cd mechanism (for Y positioning) but this turned out to be too slow and noisy as well as having no easy way to fine tune the focus.
Now looking into using one of my (5 or so) laser printer mechanisms with the spinning mirror, and a second inline PS3 servo assembly to control the focus, with an LM317 as the constant current driver and a "current mirror" to keep the burner diode below threshold except when it is writing.
So far the plan is to detect the beam start/stop positions by using two blue LEDs then use this information to control the PWM which clocks the memory, writing 1/4 of the stored data at a time corresponding to successive lines.
Writing the data into the 23K256 occurs once on each rotation of the mirror at the start of the FG pulse so the overall worst case duty cycle is 50/50 and reduces the strain on the burner diode.
Simple in theory but the chip isn't reading or writing no matter what I send to it. Its a 3.3V IC but in principle a simple resistive divider should work.
any ideas?
-Andre (have a pile of ps3 blocks here if anyone has a use)
Registered Member #1667
Joined: Sat Aug 30 2008, 09:57PM
Location:
Posts: 374
ideas? I had this idea a year ago, now a 405nm laser diode, a laser printer assembly and some dichroitic beam splitter cubes are lying in the "paused projects" box because I can't find the time to finish this neat toy. My plan was to use a red pilot laser for pcb position detection (pre-scan the whole board for alignment, this makes double-sided boards very nice and simple once autopan/autorotate is implemented). The per-pixel line scan image information is recorded using a photodiode connected to the beam splitter cubes (I hope the reflections won't make this option impossible) and a segmented photodiode from a CD drive in combination with a long focal length (50mm f/8) triplet lens assembly outside to monitor a part of the beam to adjust the height.
Focussing isn't critical here, torerance is about +/-200µm for 20mil structures.
I use an ATMega32 with 512kB of external SRAM and ethernet connection (ENC28J60), the scanner unit slows down if the cached data runs out and resumes once the buffer is refilled. Just use a bigger parallel SRAM instead, many of them are 5V types. Keep the PS3 sleds for the cubes!
>>So far the plan is to detect the beam start/stop positions by using two blue LEDs
I do not understand what this would look like. The original design of the transfer drum scanner included a slit and a photodiode that generates both a time marker and a frequency feedback to check the polygon mirror operation - the photodiode is struck six times per revolution of the polygonal mirror. The polygon mirror driver phase-locks onto a given clock signal and the inertia of the rotor keeps the anglular velocity nice and smooth, the only downside with this would be that you'd have to stream the pixel data quite rapidly. Serial SRAMs are not the optimum for this task, I prefer parallel SRAM in combination with shift registers, this leaves more time for intermediate memory access.
as to the 23x256... did you get the access sequence right as described in the datasheet? Resistors for 5V->3V will work but better add some capacitors, too. Otherwise I'm not so sure if you can reach the desired clock speeds.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062
aaaugh!!!! no i did not add any capacitors.
Interesting to see you are working along the same lines, i will have to see if this approach will work with a PS3 laser block (it has a neat focus and fine tuning servo to boot)
as for measuring the height, one way might be a spot imager using an optical mouse sensor (the adns2051) or small cmos camera.. this is used on some printers to allow ultra-fine images to be printed.
re. access sequence, i will check. i know about hold but this might not be the only problem. Confirmed it wasn't unstable power by using a lifepo4 cell.
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(Help) PCB etcher
