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Robonz wrote:Harry, what kind of laser specs would you recommend for this? 405nm mW??. Is the scan rate able to be sped up using a more powerful laser? Also what software are you using to generate the signal?. I never looked at SSTV but now I saw your glow drum it sparked my interest. i hope I did not ask too many questions.
Cheers
Keitb
Robonz wrote:I was thinking an Arduino glow drum would be fun. It could drive all the stepper motors and take bitmaps from an SD card and put them onto the glow drum.
I saw your laser driver schematic. I am not sure it is right, It looks like the laser is being driven in constant voltage mode. While you can get away with it on some lasers, I thought it should have been a constant current mode to compensate for temperature change. Maybe I am missing something
[url]lasercc.png[/url]
Harry Dalek wrote:So you know your stuff you picked the mistake i always going to update the circuit arr no ones ever going to ask me
Andrew Davie wrote:Harry Dalek wrote:So you know your stuff you picked the mistake i always going to update the circuit arr no ones ever going to ask me
I'm going to use that excuse from now on!
Robonz wrote:Interesting Harry, you really have a mix of constant current, constant voltage and linear modulation going on there. Theoretically there should only be constant current and digital control of the mosfet, but if that is working for you then that's great. Even with my poor understanding of the circuit you probably want to add a small capacitor to the laser diode + and the negative as the LM317 will not likely match the transient response you are asking from it.
I have never built a laser modulator before so its something I am keen to have a play with. When my lasers arrive I will have a crack at it and see if I can blow up some lasers haha.
For paint on the drum I have some "aqua glow powder" from Ebay. I was thinking I could mix that with some clear acrylic paint and air brush it on. Do you thing that would work?
Cheers
Keith
...with the lasers best to run it a touch below its operating voltage
Robonz wrote:Hi Harry...with the lasers best to run it a touch below its operating voltage
My point is lasers do not have an operating voltage. They only have an operating current to my knowledge. The voltage can vary during operation etc. I have some 317's coming tomorrow so will have a fiddle and see what I can come up with. I have an idea I can digital modulate the adjust pin which should make it switch more sharply. I will scope my ideas and get back to you.
I saw Bunnings had the glow paint. I am sure it is not as nice as the "aqua" powder I have, so I want to try and see if I can spread the powder evenly. I guess you need to spray paint it under a black light to see what you are doing!
Another "arr no ones ever going to ask me" on your circuit is "triangle wave" I believe it is a sawtooth when using the diode on the 555 like that.
Yes, I love the glow drum design and you are the only person I have seen to build one, very inspiring Harry!
Cheers
Keith
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