I need to know if a device exists that consists of a laser, pointed at a spinning mirror oriented at 45° such that the laser draws a line. This device would need to have an optical encoder on the motor so that, using a micro controller, the laser could be rapidly turned on and off at specific times to create a one-lined 'image'. The main component of this device would be a DC motor with built-in encoder. Are there example projects that use one? I need to be able to use this device to light up specific areas within the solid line that it is capable of creating.
The more knowledgeable among you will be able to recognize this and be able to point to devices that function similarly. There may be an off-the-shelf device that already does this on some level. Does anything come to mind?
This reminds me of the final hack-a-week from last year (Laser Oscillograph | HACK A WEEK). But that was with a scavenged linear actuator from a hard drive, mirror mech from a laser printer (IIRC), and a laser pointer.
You could potentially vary the speed of the spinning mirror..?
That's interesting but won't work for this. I need a DC motor with a high res encoder. It will just be spinning a mirror. It needs to be able to 'point' to 100 different places along a 4ft span by rapidly turning on and off as it spins.
David82:
The more knowledgeable among you will be able to recognize this and be able to point to devices that function similarly. There may be an off-the-shelf device that already does this on some level. Does anything come to mind?
Yep - it's called a photo-transistor.
Unless you've figured out a method to bounce the laser off the spinning mirror without having it suspended above or below said mirror/motor in some fashion (ok, one possibility might be a hollow-shaft motor), inevitably there are going to be at -least- one support in the way of the laser (unless the laser is far away from the mirror, hanging from the ceiling or something, and not part of the device). Since it will interfere with the laser anyhow, you could attach the photo-transistor to this support in some manner, and when the beam sweeps by, there's your timing mark. Now, all you need to do is keep the speed of the motor steady (PWM coupled with that timing pulse), then you should be able to blank the laser at will at any point in the arc, with little to no creeping caused by speed variations (because you'll be handling that as well).
Could you instead get a motor with such a optical encoder? Certainly, but why bother when you already have a laser? Another option might be to read the back-emf off the coils (this is kinda tricky, though)...
Look up crazy horse mountain in south dakota, they draw pictures on the side of a mountain during there lazer show, I think there's like 5 lazers and they are able to draw a few hundred feet large pictures, each laser being a different color
you could attach the photo-transistor to this support in some manner, and when the beam sweeps by, there's your timing mark. Now, all you need to do is keep the speed of the motor steady
You may have to try it and experiment, the laser driver may not like being switched that rapidly, and the bigger or more detailed the picture the more you need to switch it
Maybe you can switch the output or build your own driver
The Transistor as Switch section shows setup. Also read the "Connecting a transistor from the output of an IC" for an explanation of what's going on. Heck, read the whole page and you'll be a lot smarter in the end
The current drawn by a laser pointer is very low so pretty much any N-channel transistor you have will work.
Something you might have to play with is finding the right photo-transistor; most are at best sensitivity in the IR region (look at the datasheet), but you can get ones that are sensitive in other bandwidths.
Chagrin:
The Transistor as Switch section shows setup. Also read the "Connecting a transistor from the output of an IC" for an explanation of what's going on. Heck, read the whole page and you'll be a lot smarter in the end
The current drawn by a laser pointer is very low so pretty much any N-channel transistor you have will work.
Why do I need to use a transistor? If the end result is still the laser being rapidly cycled then what's wrong with just using one of the digi out pins?
