How to best control and electromagnet with sound

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Ron H
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Post by Ron H » Mon Feb 19, 2007 9:03 pm

Jollyrgr, you need a resistor or a diode (connected as voltage doubler) to GND from the junction of the coupling cap and the diode. Otherwise, the cap will just charge up during the positive peaks, and the circuit will not work.

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Post by haklesup » Mon Feb 19, 2007 9:13 pm

The easiest way to do this is to use an IC for driving an LED and drive a coil with pulsed DC instead. The slow mechanical response time of the fluid would make any AC signal useless. If you could, you could make its surface emit sound.

Take for exmple a LED VU meter chip. It has 10 or 12 outputs which drive LEDs as the volume increases. Instead of LEDs imagine a series of electromagnet coils positioned any way you want They could be additive like a multi tap coil or in an array; 2D or 3D. Remember, the direction of the twist determines if two coils add or subtract fields.

The LED driver output on the IC is good for a few 10s of mA maybe 150mA so if you need more current (and this depends on the number of turns in your coils and the resopnse of the fluid and the reach of the field you desire) you will need to buffer the IC outputs with transistors (like is often done to drive a relay coil). It's all in the IC data sheet once you choose one.

If a VU meter is not what you want, do a little digging on audio IC and LED and you're sure to come up with others that are frequency dependent and some with variable response time. A spectrum analyzer display would be perfect (like from the front of an EQ). A clock display would also be pretty cool or a 16x16 dot matrix. The list goes on.

I would start out making some coils to move the fluid around and experiment with a plain old DC supply to determine the optimal shape, number of turns, type of wire, wire gague, voltage and current. You'll probably need a series resistor to keep the current under control as the coils will inevitably only be a few ohms max. Once you know range of drive current thats effective, you can design the interface to the IC (or if you even need one).

To make coils use coated wire wrap wire in coils or pancake spirals. Use metal, and non metal forms of various diameter for the coils and plastic cards to glue the pancake coils onto. You can use any wire you want as long as the coils don't short across the windings or in the fluid but #30 kynar wire wrap wire can take over 150mA and probably well over an amp when cooled in the fluid. (use standard wire heating tables)

This could be a really cool and visual project. If you do complete it, don't forget to YouTube it and post a link here.

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