Well I was searching for a good forum for Hobbyist. What read here is mostly over my head. Hopefully you fine members will help me out.

What I am looking for is a simple circuit that will measure resistance between 0 and 5k and display the amount on a small digital screen.

I usually buy my parts from Digikey.ca or Jameco.

Any help would be appreciated!!

 

It's called a multimeter and can be purchased from all good electronics stores.

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Sorry I should have been more secific. I am not really that stupid. I have more then one multimeter.

I want to built this circuit into another project I am working on!!

 

EDIT: Oops, you wanted to measure resistance and not voltage. But pretty much the same thing still works- just use the resistance being measured as one of the resistors in theh resistive divider and the voltage measured will be proportional. YOu have to be able to apply a known voltage across the resisitive divider though.

 

Two methods spring to mind.

Connect the resistor to a constant voltage source and measure the current.

Connect the resistor to a constant current source and measure the voltage,

You can get LCD pannel meters that display current or voltage and you can normally set the scale yourself.

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Here's an example of a complete meter in one IC plus display:

http://rocky.digikey.com/WebLib/NJR%...U9201B_02B.pdf

It may look complicated, but has lots of good features and won't take much work to implement.

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RadioRon

 

Sorry guys. I think I am in over my head. I can get 5v or 12v to the 5K pot but not sure how to make resistance show on a LCD screen yet. I will do some more reading!!!

 

Ok so far I have figured out that I will need two resistors. One a constant resistance and the other the variable. power supplied to the resistors in parallel, the output of variable resistor to ground, measure the output voltage from constant resistor use formula to find the resistance of variable.

Now how do I get this to an LCD screen?


Now I am right thread. LOL

 

use a A/D converter to measure the voltage, Once it is digital you can easily display it on your display

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Khizer Naeem Mughal
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I hope you know how to display some thing on the LCD.

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Khizer Naeem Mughal
IIUI

 

sorry nope. Like I said over my head I think. It's actually the resistance I want shown on screen.

 

Ok maybe some one can point me to some reading material I can get. Or Free-to-Web reading.

ThankX

 

You can buy panel meters that display voltages between 0 and 10V, see Google for places where you can buy them from.

You can create a constant current source using an op-amp.

RL is your 0 to 5k variable resistor.

Rsc is a sense resistor.

Vref is a stable reference voltage.



In the example below.

Vref = 1V
Rsc = 1k

Therefore the current flowing through RL::


Ohm's law states that V = IR which means that when the resistance is 5k 0.001 * 5000 = 5V so all you need to do is connect your panel meter's input across RL and (assuming it's input impedance is very high, >10M) you'll read 0 to 5V which corresponds to 0 to 5k for Rl.

To get V_ref I'd power the whole circuit of a 12V regulated supply and use a 2K 22k potential divider to get 1V.

Not that the op-amp needs to be able to accept input voltages down to 1V and output voltages down to 1V, an LM358 or MC33171 (I recommend the latter) will do fine. Also Rsc can be made smaller by adding another non-inverting gain stage or the output of the whole circuit can be amplified using a differential amplifier if needs must.

Attached Images

Constant current.png (15.4 KB, 7 views)

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Start here: http://www.electro-tech-online.com/m...d-upd-0xd.html
Nigel’s joystick tutorial uses R/C timing to measure resistance and displays on an LCD. If you can’t calibrate it to actual ohm value, at least it will be a real good start.

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