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A New Laser and Laser Control

A project log for Laser Galvo Clock

Clock projected onto the wall with cheap laser galvos

Alan GreenAlan Green 07/16/2019 at 08:330 Comments

Two exciting developments today. 

A New Laser

In comments on a previous log, [Stefan Kruger] reminded me that common, cheap, poorly designed 532nm laser pointers also emit a surprising amount of infrared light, which is a potential danger. He  referenced this great paper from NIST, which features a laser pointer very similar to the one that donated my previous green laser.

After a bit of research, I ended up buying a 50mW 505nm laser, which does not have the same problem. 

Photo from the eBay listing

The driver board I received looks a little different, and it has both "TTL" and analog inputs. 

Laser Control

I hooked up the "TTL" input to my PIC32 and it Pretty Much Just Worked. Here's a cross-in-a-square test pattern, which demonstrates the laser can be turned off between drawing the square and drawing the cross.

Same pattern as before, but without the excess lines
Look ma! No unwanted lines!

One change I made: I moved the laser control to a 5V tolerant pin since the input is marked "TTL" and it wouldn't be unreasonable to find 5V their at some point. However, the input pin seems to float at around 1.8V, and connecting the pin to ground turns the laser off. Therefore, I set the PIC's output to use an open drain.

Next

I'm working on plans to mount all this hardware on the ceiling of my kitchen. I'm using Fusion 360 to model all the components so I can figure out how to place them and where all the holes need to go. It's taking a while, but I did make this blocky but dimensionally accurate laser galvo model.

Another thing that needs doing is to rewrite the PIC32's DAC output loop. It has two problems. First, it's too slow to output 20,000 points per second to the galvos. Second, there's a bug in there because it seems to stop working from time to time. A rewrite will fix both.

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