Ohm Meter

[Duckvader]

Hi.
I am interested in creating a simple ohm meter circuit.
Can anyone help me on this.
I don't mind creating a digital ohm meter or an anolog one just for fun.
Really can't find a suitable site for this.
Hope someone can give me some highlights on how to create one.

The difficult part is creating the suitable negative and positive electrodes to take measurements. What can i use for this???

The scale part isn't any problem as i can buy it or detach one from my AM Meter that is quite cheap, small in size and easily found not the same for an Ohm meter.

How can I control the range of scale measurement is also an advantage.

THX. ;-)

 

[Nigel Goodwin]

I'll give you a hint!.

Do like modern digital meters do, feed the resistor under test from a constant current source - and simply read the voltage dropped across it. This gives a forward reading scale, and is also linear - far easier than the backward reading non-linear method.

 

[HiTech]

I'm not sure if I follow you correctly but unless you are fixated on building one for fun and personal satisfaction, you can buy a fairly accurate one for a mere $3 US. And you get other functions as well as various ranges. I have a half-dozen of these little cheapies.... cheap in price but not in performance. Heck, I even used one in a pinch to troubleshoot a $2000 computer! I have disassembled the case, removed the innards, place a few jumper wires across the switch/range needed and voila! I have a digital voltmeter and ammeter readout for a variable, bench power supply. Cut rectangular openings in the power supply's front panel for the digital displays.
Those Chinese are amazing on what they'll slave over for a bowl of rice and some bok-choy!

https://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=90899

**broken link removed**

 

[Optikon]

I'll give you a hint!.

Do like modern digital meters do, feed the resistor under test from a constant current source - and simply read the voltage dropped across it. This gives a forward reading scale, and is also linear - far easier than the backward reading non-linear method.

until you get to 100Meg or higher range... (too hard to make an accurate pA current source) then you need to go to constant voltage mode and measure current.

 

[Nigel Goodwin]

until you get to 100Meg or higher range... (too hard to make an accurate pA current source) then you need to go to constant voltage mode and measure current.

Depends on the voltage you use!

Considering 100Meg resistors are generally for VERY high voltages, it makes sense to test them at that!.