Need a simple method of blocking a light beam

Hobby servo? Clip a playing card, credit card, etc. onto the horn. Operate it with an easly-built servo tester, maybe even replacing the pot. with a switch & resistors.

JM

Do you have any links to vendors of hobby servo's?

In the US, try Tower Hobbies at the obvious URL.

Best regards, Spehro Pefhany

Swivel a pair of polarizing filters or shine it through an old LCD panel which is wired to go completely black.

----------------------------------------------------------------------- Ashley Clarke

This seems to work:

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Rotary solenoids are often used for this. You don't need a servo driver for each one then, just apply voltage and it rotates 90 degrees (or whatever spec), remove voltage and it goes back.

-Daniel

Marco,

You can find servos and serial port interface servo controllers at

That's the easiest way to get from PC to motion without any hassle. There are many things you could build with solenoids, servos, PICS, AVR's, Basic Stamps, etc. But they all require some building and/or programming. Servos + SSC-12 + Serial port = easy.

--TE

For my holography experiments, I wanted something more precise.

I used the voice coil from a hard drive and a small H-bridge connected to a microcontroller.

Humm, that's a good use for those old ancient 8" and 14" hard disk drive units. Most of them used a voice coil arm for moving the read/write heads back and forth. Come to think of it, the last batch of 3.5" HD's and 5.25" HD's I took apart, used a magnet voice coil arrangement too. In this case they used a pivoting arm. It wouldn't be too hard to hack one of these out nicely. Watch out for the magnets though, everything sticks to them really well. Use an h-bridge and PWM to position the arm.

Yup,

Lucas Ledex.

Mike

Thanks, but I can't add anything to the optical path when the shutter is open. This is being used in an instrument which will be making relative phase measurements of the paths of different parts of the beams using interferometry. The reflection off the surface of a shutter will cause interference itself. Additionally when the shutter was open, the imperfections of the polarizing filters would cause problems. We're sensitive to just a few nanometers of path difference.

Marco

Tower Hobbies is a good inexpensive source for standard types of hobby servos. If you can solder, you can make an inexpensive servo controller from a Kronosrobotics servo control chip. Control of the servos is easy just using batch files. The below link shows a simple setup for controling servos via batch files or a web page.

"Earl Bollinger" wrote in news: snipped-for-privacy@comcast.com:

Do you have an example of circuit to drive these new voice coils? I'm very interested because the only thing I found on internet was that it is a little bit hard to drive these voice coils very accuratly. Even the hard disk manufacturer encode correcting information for the voice coil directly on the disk plate to react accordingly to its position (of the head). After reading this article, my only idea was to forget voice coil and think to another solution. So if you have any informtion that can leverage my knowledge about this, it will be greatly appreciated. Thanks

Sebastos99

ps: for information

download PDF file, see page 16-19), the magnets for hard disk drive are samarium magnets (high energy material magnet). It can pinch the skin of your finger really highly.

maybe lcd shutters from modern slr's, maybe playing with the bias voltage on a regular lcd panel will do the trick.

On a hard drive, very accurately means moving it to precisely one of thousands of positions. You only need two positions, one that covers the laser and one that doesn't. The most recent drives I've taken apart were a big 5 1/4" full height 30 Meg from an AT-compatible. They've got the strong magnets and a coil with not-many-turns in it so that it would MOVE when 5 volts was applied (I never actually tried putting voltage across the coil now I'll have to take apart another one), but it probably takes a big chunk of current (have a 1-amp or better variable supply handy), and could get from one end to the other in a small fraction of a second (I forget what the max seek times were supposed to be). Measure the coil resistance to get an idea of how much current it will pull. Try putting about a quarter volt across the coil in one direction, then a quarter volt in the other, see if that's enough to get it to move back and forth. Keep increasing the voltage a little at a time until it responds fast enough for you. At a reduced voltage, a 1/4 second pulse may be enough to make it go from one extreme to the other. If you don't mind it hitting the endstops (and it doesn't bounce back!), that should work okay. If you want this thing to do thousands and thousands of actuations reliably, you should time and sequence the voltage pulses (say, using

2V, 150mS positive to accelerate it, then 150mS negative to decelerate it (maybe a shorter decelleration time to account for friction) - to move it back, do 150mS negative then 150mS positive), so that it moves back and forth smoothly, accelerating and decellerating without banging the stops.

This should be a lot simpler than the original application of precisely moving the heads. Maybe this will make up for my posting the Google link. :)

I just googled for Hard drive voice coil and this is the fourth link returned, perhaps you'll find it relevant:

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That's a $4 rotary solenoid, but it's duty cycle is questionable.

The hologram guys have been known to bastardize a small analog volt/mili-amp-meter and stick a black shutter on the needle. It's delicate, but it produces virtually NO vibration when it's activated.

Try that. With the appropriate resistor, you could probably hook it directly to TTL.

Andy

Ben Bradley wrote in news: snipped-for-privacy@4ax.com:

Thank you Ben for this link. I googled your words and it works. Don't understand what happened for me. I am not good in english but not at this point :) (I hope) May be, I've added some noisy words in my request. Thanks

Sebastien

ps: gold number is also an interesting number. May be there is a relationship between gold number digit series and (series of) gap (difference) between prime numbers...