Simple Meter

[Abbell]

Preface: Understand, I know just enough about electronics to be dangerous... so pretend I know nothing as it will be close to reality.

I am trying to figure out how to build a simple Ohmmeter. The goal is to measure the resistance of a heating wire on a small scale.

The circuit requirements are 3vdc and to measure 0-10 Ohm of resistance accurate to .1 possibly .01. The output will go to a LED diplay and all will be mounted in a AA battery box.
Here are the basic components... the suppliers are just who I found the parts fastest at for reference purposes.


What I want it to do is basically the same function as
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This is the goal... they are out of stock and I want to build my own device. The form factor is excellent for its application.
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Project form factor:
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The output:
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I was thinking that I would need an operational amplifier. Then set it up to show on the display the inverted voltage results. So when the resistance is added to the circuit the display would scale upward/downward based on the wire resistance.

I have seen several schematics that are very close to what I want, but my needs are far simpler than most of the options.

I was thinking about the LM741 as control. I understand the basics, but I am lost in the circuit details.

Any help would be GREATLY appreciated.

 

[alec_t]

Welcome to the forum .

I have seen several schematics that are very close to what I want, but my needs are far simpler than most of the options.

To get the accuracy you want for resistance values of only a few Ohms and with only a 3V supply is not simple. It would probably be cheaper to buy a meter/kit than to try and source individual components. Whatever you do, don't use the out-dated LM741! A micro-controller with built-in ADC would be one solution.

 

[Abbell]

Welcome to the forum .
To get the accuracy you want for resistance values of only a few Ohms and with only a 3V supply is not simple. It would probably be cheaper to buy a meter/kit than to try and source individual components. Whatever you do, don't use the out-dated LM741! A micro-controller with built-in ADC would be one solution.

It would be cheaper for me to buy the kit that already does the job... would be cheaper for me to just use the panel that already does the job. It would be less headache to use one of the dozens of mutimeters or the oscilloscope I already have to do the job. I know the job can be done... I am looking for THIS solution.

It is the elegance of the solution. I have held the end result in my hand. I could buy the kit if it was ever in stock for more than a few hours. So far the other forums keep trying to give me complex solutions. I am no electrical engineer, nor do I play one on TV.

I just read up on the " What can be done with a micro-controller with built-in ADC?"... seems like trying to take an elephant to New York's central park. You can do it, but who wants to carry the baggy

 

[Abbell]

If it works this time...here is the actual circuit using a .56 size led segment in the device I like:

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Backside

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and...the full device inside a 3 X AA box powered by 2 X AA and circuit occupies the center.
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and a picture of the disassembled pieces

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[alec_t]

Very nice. Elephant or no, be assured that circuit board with the display mounted on it has a micro-controller on there somewhere!