Blanking delay

[buffo]

This would require a constant scan rate, right?

The setting will scale with scan rate, but yes, you may need to alter it slightly if you make large changes in scan speed.

I'm still trying to increase maximum scan rate so I have to make the delay adjustable

Well, it needs to be adjustable anyway, so you can set it the first time!

But yeah, once you get it set, you normally don't change it. Just like scan speed - once you set it, you leave it there. (Because if you scan at different speeds, you really need to re-tune your scanners to get optimal performance.)

I'm impressed with the image quality you're getting. You've obviously done a great job building those scanners!

Adam

[Danny]

Very nice value. My current 7K-8K homemade galvos with their drivers reqiure about 3A X 22V (bipolar).

Yes, I think they are really effective. This is nice since I will be running the projector on batteries but I would have liked a higher scan rate. I have a theory on how they got that fast despite the low drive current. They are made of plastic(!). This meens that I have huge problems with heat dissipation but in return no eddy currents are formed to slow down the rotor. Any conducting material near the rotating neodymium magnet would cause a opposing magnetic field as the magnet moves. That was why I used plastic... The magnetic coupling between coil and rotor is also quite close. The L/R time constant of the drive coil is also important... I'm running both galvos of a +/-15V 1.5A DC/DC converter.

When I started this thread it was about blanking delay... I will shut up now or start a new thread on galvo design Thanks for your positive comments. I'm gonna try to solve the issues with heat dissipation in my mk2 galvo. For now I'll try to tune the galvos for a lower scan angle and hope to get better scan rates.

[James Lehman]

What are you using for a DAC? Where are the signals coming from? Is all that your design as well?

James.

[Danny]

I'm using two serial 10-bit DAC IC's fed from a microcontroller. This is connected to my PC through the printer port and the microcontroller is emulating a DAC0832. I did it this way because I had the DAC IC's laying around at home, and I also wanted to be able to add a few features later. I will add support for reading images from an SD memory card (eliminating the PC). I also thought of creating a "game mode" to play a simple pong game directly on the projector. It's ment to be fully portable too for some serious outdoor fun

[James Lehman]

Does it have an ILDA port?

James.

[Danny]

Nope! I'm using my own standards!

[James Lehman]

I can dig it.

James.

[mixedgas]

Nope! I'm using my own standards!

dont even think! of shutting up! nice work! And keep this thread ;')

getting rid of eddy currents is nice trick!
if you have graphics/modulation questions PM with a phone number and I can walk you through the basics.


whats your jump time in microseconds on a scope for a 2.5' jump? A 10' jump?
Steve

[Danny]

getting rid of eddy currents is nice trick!
whats your jump time in microseconds on a scope for a 2.5' jump? A 10' jump?
Steve

Yes, I think the eddy currents can be a real problem. The faster the rotor tries to move the more the opposing magnetic field will try to brake it. This force can be really strong. Try this experiment sometime: Drop a neodumium magnet between the fins of a aluminum cooler. It will slooowly slide down. Looks absolutely fascinating!

This project has been on ice for a while now. I don't remember the step respose time exactly. I think it was somewhere between 500-700us at it's best (dont remember at what angle though). I think the time constant (L/R) of the coils where somewhere near 40us wich correspended exactly to the phase lag between a square wave input signal and galvo movement.

I would like to build new galvos using a ceramic material (like in the washers used to electrically insulate power transistors from their coolers) to dissipate the heat. I'm also thinking of water cooling to really overdo it the next time This would mean building a completely new projector. All that stuff is NOT going to fit in my cheap flightcase. I will complete this first and then mayby start all over again... I'm just dreaming about the speed I could reach if my galvos could take like ten times the current I'm feeding them today... I'm also thinking of a two or three phase coil system with corresponding drivers to increase speed. As I said: I make my own standards!

[mixedgas]

there are some near zero inerta galvo sized motors with 3 phase coils to drive them. Bill Benner from Pangolin brought some to a conference once, very cheap and galvo sized from Faulhaber Motor. If somebody figgured out how to do a fast lookup table from differential to three phase, and we used back EMF for position feedback, they would approach 30K,have real bearings, be swiss made, and indestructable, as well as possibly cheaper then chinese galvos. I know how to do the back EMF part.

at 400-700 uS jump, your 1/2 way there to the older professional grade galvos. That rocks. If you have access to the lathe, I am just about to throw out some macor like machinable ceramic, you lathe it then fire it in a oven to harden it. Firing oven is not that hot, like 900C, which is a off the shelf cheap tube furnace with nichrome elements. it does shink a little after firing, but that is a known quanity.

keep us informed.

Steve