Actually, giving it another thought, the cheapest and easiest,would probably be to use the innards of an old mouse.
Wrap a spring-loaded string (waxed?) several turns around the shaft of one of those small wheels in the mouse. Remember the frequency indicators on real old radios? (In this case it will be the string moving the axle, not the axle moving the string).

Hook up a scope to the mouse: pin 5 is ground. Pin 2 or 3 is output, and one of the other pins supply the power.
Examine the output.
Your circuit will have to be designed to remember the last position before power-down, or you can simply move the manifold to an end-stop and reset the position counter.

Finn

Finn Lassen wrote:

Hi Ed,

This is off-the-wall, but what is used in the $20 electronic dial calibers? Maybe it's possible to pick up the signals to the LCD segements... I told you it was off the wall.

Now, you can make your own:
Need a strip of binary tape: one strip is black 1/2 the length white the rest, the second stripe is black-white-black-white, the third twice as many black-whites, etc. down to the resolution you want. Then a number of led/photo-transistors pickups that can read the stripes.

The easier way is of course just one stripe and your circuit just counts the changes as the stripe passes through the led/photo-transistors reader - but requires the circuit remembers the current position. Also some way to determine direction.

Take apart an old mouse and see how that works.

There must be 10's of ways to do this.

Finn

Ed Anderson wrote:

Hi Guys,

 

    I am finishing up the design and fabrication of my variable length EDDIE intake and need some assistance.  I want to use a voltmeter (or LEDs) to indicate the postion of the manifold.  The simplist approach would appear to have a linear resistor attached such that its arm is moved as the manifold moves thereby changing the resistance indicating distance. 

 

I've done a lot of Web surfing and found a number of linear postion potentiometers.  The problem is they cost more than I have invested in the manifold.  Regular audio linear potentiometers do not have the mechanical range I need.  I need a position indictor that has at least 5 1/2 - 6" of travel.  Anyone have any ideal where something reasonably priced might be found. 

 

 If you know of a retail catalog that have such things I'd appreciate a pointer.  I can find plenty of Linear Postion Potentiometers - but they cost in the hunderds of $$.  Need something much cheaper. 

 

I know I could devise a 3:1 lever ratio or some such thing and use one of the cheap (but mechanically range restricted) linear potentiometers for audio circuits, but would rather not.

 

Thanks

 

 

Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC