Hi.


We have been working on a small project trying to build a fun game but are having some issues. We basically need an oscillator that can be controlled by varying the distance between our hands and a metal plate (capacitor type of sensor), which then the signal converts into a PWM signal and is fed to a H-bridge that controls the fans. Our issue is the sensor part, oscillator and the converting into a decent PWM signal that idealy would go from 0-100% based on the capacitance. We have tried several types, relaxtion oscillator (square), 7414 schmitt trigger (square) and recently I also built a Variable pitch oscillator taken from a theremin guide, which generated a nice sine wave but only varied from the intervals 120-142kHz. We also could't figure out how to utilize it.

Is there any kind soul that have a great idea of how to make this a reality? Basically what we need is an oscillator that can be affected by just one capacitor where the interval of the capacitance (the hand) is around 20pF, this oscillation then somehow needs to be converted into a PWM signal. Our only challenge here is that we are limited to only analog components but pretty much have anything at our disposal, but mostly standard components, and also the 7414 is something we managed to get our hands on. We have tried to come up with a solution for a long time at a daily basis and are getting pretty frustrated.

Thank you in advance,

Chris.

 

Google "Theremin" for info on how to do it.

 

I was just involved in a discussion with another member who was kind enough to share one of his completed projects with me which he originally posted some time ago.
Project: "Color Theremin" capacitive sensing LED toy
You may want to check that project out. While the capacitive sensing was used to drive a LED the principal of operation can be applied to anything you wish to PWM. Using the bottoms of aluminum cans for sensors was a nice touch and all of the work is done using the uC (micro-controller) in this case a relatively inexpensive Arduino served the bill well. The micro-controller could easily drive a few MOSFETS which in turn would drive your fans.

Ron

 

Our only challenge here is that we are limited to only analog components but pretty much have anything at our disposal, but mostly standard components, and also the 7414 is something we managed to get our hands on. We have tried to come up with a solution for a long time at a daily basis and are getting pretty frustrated.

Sorry as I just caught the latter so using a uC is out.

Ron

 

we are limited to only analog components

Why? Is this a school/college assignment with restrictions on allowable components?

 

Why? Is this a school/college assignment with restrictions on allowable components?

I have seen this sort of thing before where rather than using a uC they want students to use discreet components. I am not sure of the motive other than teaching discreet building blocks to solve a circuit rather than an integration of the blocks into a uC. While I do not see it as practical it seems to come along quite a bit.

Ron