loudspeaker problem in fringe locking circuit

These are all of the old posts from the first two years of the forum. They are locked.
Updated: 2005-03-28 by HoloM (the god)
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Thilo K.

loudspeaker problem in fringe locking circuit

Post by Thilo K. »

Hello. A few hours ago, I tried out the circuit for fringe locking being suggested here. Somewhere I read that the mirror is to be mounted on the speaker, so this was what I did:

1. The speaker is protected (?) by a cylindrical something having a hole in its middle on top of it. It is too small to put the 1x1cm(0,4x0,4 inch) mirror in it and there ought to be a 90° angle of incidence to get the point in and out.

2. So I cut off the top and saw a white circle mounted on a shiny surface. I removed the circle and I - occasionally - broke two of three connections, which were also holding the surface in position under the surface. That made me think about something: How can you use a glass mirror on such a tender spot ? How does this work ? The mirror will cut off all connections for sure - it is far too heavy for that thin metallic surface.
Colin Kaminski

loudspeaker problem in fringe locking circuit

Post by Colin Kaminski »

I have not assembled my fringe locker yet as I am hoping to make some holograms before I go back into testing. I have two of the speakers Joe recommends and they look pretty stable. I plan to glue the mirror to the center of the cone with silicon.

The mirror I have is part number: NT43-854

from Edmund:

http://www.edmundoptics.com/IOD/Display ... uctid=1743

It is small, light and inexpensive. It also will reflect 96.5% of the light at 650nm.

It is very small compared to the speaker and I don't think I will have to modify it at all.
Thilo K.

loudspeaker problem in fringe locking circuit

Post by Thilo K. »

Even if the speaker works somehow, how can I test the circuit using a DMM ? What should it do ? Change current or voltage ( both in which areas ?) and when ?
And all other questions that aim at checking out the function of the circuit
Can you or someone else help me with this problem ?
Thilo K.

loudspeaker problem in fringe locking circuit

Post by Thilo K. »


Colin Kaminski

loudspeaker problem in fringe locking circuit

Post by Colin Kaminski »

Perhaps because I have been looking at a Michelson interferometer for months, I would test it in a Michelson interferometer. I am under the impression that it is important to have the two sensors straddling a single fringe. This would be easy in a interferometer.

If you set the DMM to voltage and read the voltage to the speaker leads you can see the corrections the locker is making. Better yet would be an oscilloscope.

Everything I read suggests the fringe locker signal should be used to diagnose the problems as opposed as the final solution to the problems.

Thilo K.

loudspeaker problem in fringe locking circuit

Post by Thilo K. »

But... don´t photodiodes work due to the photoeletrical effect that states there is a change in current which is directly proportional to incoming light energy E = h*f - W ?
A very general question i know...
Colin Kaminski

loudspeaker problem in fringe locking circuit

Post by Colin Kaminski »

Thilo, We are beyond my knowledge but it is something like: the bias resistor converts the current from the diode into a voltage source so the op amp can amplify it and send it to the speaker. I do know the speaker is looking for a changing voltage.
Thilo K.

loudspeaker problem in fringe locking circuit

Post by Thilo K. »

That´s an understandable explanation of the phenomenon. Thanks.
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