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I'm working on a VHS adapter that uses a VHS Cassette casing with some electronics in it. The hardware contains a battery and some sort of IC which I can Not program, it's not a micro controller, it's a fixed piece of hardware that does a specific task.

I do not want to use a microcontroller, the hardware that I use is the only hardware that I am allowed to use because of energy efficiency reasons.

To run the hardware I use a 3.7 V LiPo battery and the only thing I need now is an analog/mechanical momentary switch which is linked mechanically/magnetically (preferred) to one of the wheels of the VHS Cassette.

This momentary switch makes sure that the hardware is powered ONLY when the VHS Cassette wheel is spinning.

How do I create such a momentary switch?

I have one solutions to this but then again I'm not sure how to accomplish it.

Solution: Putting a magnet on one of the wheels, and use a reed switch to charge a capacitor that in turn powers the rest of the hardware.

Pros: should be really cheap, is more or less solid state. Awesome!

Remember the following things:

I only allowed to use the hardware mentioned: The IC, the battery and a momentary switch. -There should be as little moving parts as possible, it's preferred to be completely solid state. -No digital sensors allowed. -No microcontroller allowed.

Illustration: enter image description here

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It is not really clear what you are trying to do. If I ignore the bit about "current flowing" then it looks as if you want a signal that indicates there is motion of the "motor." Are you actually trying to detect a motor moving, or some other object? Different methods can be applied in either cases.

Inferring that you are trying to detect that some object is moving in a repeatable fashion and you need to do so without physical contact with that object, my suggestion is attach an object that can be detected to the moving part and put a sensor on the fixed part.

If the moving part is indeed a VCR cassette, then a magnet is a bad idea as it will affect the recording on the tape. So let's use a reflector on the moving bit and a reflective optical sensor on the fixed part. The sensor looks like this

enter image description here

Similar sensors can be purchased here. They combine an infrared emitter and a photodiode. The light goes out the emitter, reflects off the sensor and is detected by the diode.

That sensor will produce a pulse on the output when the reflector is seen. To extend the length of the pulse so it lasts for a full rotation before being triggered again, a circuit called a one-shot multivibrator can be used

enter image description here

This circuit will provide a constant signal as long as the rotation continues. After one full period without the rotating sensor being detected, the signal will shut off.

Hope that helped.

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  • \$\begingroup\$ Hmmm... I'm not really trying to detect a movement, well in a sense yes, but it has to be completely mechanical. What I want to do is to mechanically maintain power while the cassette wheel is spinning. As soon as the cassette wheel stops spinning, the circuit is broken. So using extra electronics doing so would slowly drain the battery, I need effiecency as well as functionality. \$\endgroup\$
    – xaid
    Aug 9 '13 at 7:19
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A tachometer that spins with the motor (via mechanical linkage, if that's OK), and then gated with a comparator to define your minimum velocity that you would like to be "on" would do the trick with analog techniques

A quadrature encoder can be used, taking output from either bit, and use that to trigger a retriggerable one-shot with the output pulse width set for your minimum speed. Then, invert the output of the one-shot. This comes close, but has a variety of issues, like what would happen during very slow rotation would look like "on off off off off off on off off off off off .....

As a kid, I had a yo-yo where centripetal force would force contacts out and make the yo-yo light up when it was spinning. You could use a similar method with mechanics, or with an eccentrically mounted accelerometer.

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  • \$\begingroup\$ Hello Scoot. What you suggested is very interesting, do you have any links to some documentation so I can see if that is what I need? thank you. \$\endgroup\$
    – xaid
    Aug 9 '13 at 7:23

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