Making your own ohm meter – help needed!

[Ja7me]

Hello everyone,

I am attempting to make my own low ohm meter in the range of 0 – 100 Ohms.
I have based my circuit on the design shown in the link below:
https://www.electronics-diy.com/electronic_schematic.php?id=951
The circuit kind of works ok, however I would like more stability in the readings I get. I measured across a 2.2ohm resistor and was getting fluctuating readings between 1.8ohm and 3ohms on my panel readout display.
When I use my digital multi-meter in replace of the panel meter I get a stable reading close to 2.2ohms.

Is there anything I can do to make this circuit more stable?
Do I need a different panel meter voltage readout display?
I would be very grateful if anyone can help me with this project.

Regards,

Jamie.

 

[chemelec]

It Would be Nice for peope who Steal Circuits to Show the Origional Owners Article.
https://www.electronics-diy.com/electronic_schematic.php?id=951

The above Ohm-Meter has been taken From MY WEBSITE, WITHOUT PERMISSION!


Not sure How you modified my circuit, But it can easily be made to read between 0 and 100 ohms.
And it Should be VERY STABLE.

Possibly Something Wrong with your: "panal readout display"?

 

[KeepItSimpleStupid]

Can you post some info about the panel meter?

You did use two batteries, right?

Could be as simple as the (-) side of the battery has to be connected to the (-) side of the meter with or without a resistor.
With the leads shorted on the panel meter does the meter read zero?

 

[JimB]

Chemelec wrote:

It Would be Nice for peope who Steal Circuits to Show the Origional Owners Article.

How galling!
Not even an attempt to redraw the schematic and paraphrase the text.

Reminds me of something a couple of years ago where some Indian guy had ripped of some work from the website of a guy here on ETO (Ikalogic ?) and was blatantly claiming as it as his own work.
Not good.

JimB

 

[Ian Rogers]

At least he kept your name on the schematic......

 

[chemelec]

At least he kept your name on the schematic......

Yes, I will give him credit for that.
But showing my Wesite Link would have been Most Appropriate.

 

[ikelectro]

It Would be Nice for peope who Steal Circuits to Show the Origional Owners Article.
https://www.electronics-diy.com/electronic_schematic.php?id=951

The above Ohm-Meter has been taken From MY WEBSITE, WITHOUT PERMISSION!


Not sure How you modified my circuit, But it can easily be made to read between 0 and 100 ohms.
And it Should be VERY STABLE.

Possibly Something Wrong with your: "panal readout display"?

is there any chances to make a mili ohm meter???
if yes. it'll be vary helpful to me. and how to mak it???

 

[chemelec]

is there any chances to make a mili ohm meter???
if yes. it'll be vary helpful to me. and how to mak it???

It is a Milli-Ohm Meter. (Down to 0.001)
But it also goes up to 1.999 Ohms

A Kit of Parts/PCB is Available from me.

 

[alec_t]

Have you checked that both batteries are fresh?

 

[Ja7me]

Hi everyone,

I would like to first apologise for my very delayed response, I lost my password login details and have only just found them again. Also I would like to apologise to chemelec, I assumed your schematic was online for everyone to share, I did not realise I should have asked your permission first. I am new to electronics and just wanted to experiment with it. Making an ohm meter seemed a good way to start learning about electronics.

If you are all still willing to help me, I have attached another schematic of the circuit. the circuit is based on Gary Lecomte design from his website:

Instead of using two different power sources I have just used one, being 6V. This seems to work ok with the particular panel display I have.

Previously I came to the conclusion that the panel meter display itself was inaccurate. I have recently purchased a good quality one from Farnell (order number: 9932801). However I am still getting the same problems as before, the display does not show the readings I would expect.

I have modified the circuit so that there is a source current of about 10mA, I done this using a 120ohm resistor for Ra.

From my findings below you can see that the panel meter display does not show vload accurately. I find this confusing as these panel meter displays are meant to show milli-volts accurately.


LOW OHM METER FINDINGS:

Parts:

Regulator = LM317
Ra = Adjustment resistor
Rload = Resistor to be measured
Vs = 6V

When:

Ra = 120Ohm
Rload = 2.2Ohm
Vload = 0.024
Panel meter reads 1.87

When:

Ra = 120Ohm
Rload = 4.4Ohm
Vload = 0.047
Panel meter reads 4.10

I really would be thankful for some help on this one, I have no idea why these displays should not read an accurate reading.

 

[chemelec]

Most Panal Meters require a Seperate Power supply.
Some will work with One Supply, If the supply is only 5 Volts.

So I suggest you Try a Seperate Battery for the Meter.

Or it could be your 120 Ohm resisor is OFF in Value.
Most resistors are +/- 5%

 

[Ja7me]

Thats everyone for your suggestions, I will try everything you have all mentioned

 

[Ja7me]

ok thanks i will try using a seperate supply for this