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Hello. I am doing a school report and I need to draw the schematics. We measured resistances, so I need to place an Ohmmeter, but I can't seem to find it. How can I do it? Seems strange that something as simple as an Ohmmeter doesn't exist...

Hi Alegom,

I’m also new to “virtual electronics” and found it strange, too. It would be a nice feature, but to measure resistance is not in the focus of simulating the behavior of electronic circuits. This doesn’t mean it wouldn’t be possible.

Compare it to a mountain bike.

Nice.

But one may ask “And where is the trunk?”

;-)

Regards, Sancho

See this thread:

https://www.circuitlab.com/forums/support/topic/2qz8k3md/how-to-measure-resistance/

and:

They don't give you an ohmeter symbol but they do give you ways to measure resistance.

:)

@Sancho_P

Yes, I completely understand that the point of all this is to do the circuit simulation, but it sucks. Then I just hope they implement this feature. It should not be that dificult, I believe. For those who did everything else, at least... :S

@signality

I had already conduted a search, and I remember that topic. What I really need is that ohmmeter symbol, for design purposes (reproduce the circuit used in the lab). But thank you anyway, for your help. ;)

Except maybe MultiSIm, I don't know of any simulator that offers an Ohmeter functional block with a suitable symbol.

They tend to be left to the user to implement, very much as in CL.

@signality: I’m with @Alegom here, because CL is not the fully fledged electronics simulator, but on the contrary, it is a very useful tool for beginners (like me) in simulation. It is ideal also for beginners in electronics (well, the documentation is OK, but not as excellent in this aspect as the editor itself - just my opinion).

I think the resistance in CL is a bit in the shade of voltage and current:

1) There is a voltmeter and an ammeter, but no ohmmeter.

2) There is a behavioral voltage and current source, but no “behavioral” resistance source.

Regarding the latter I’ll soon publish a circuit using a NTC and I’d love to use expressions as a source of resistance …

Yes, I know about expressing resistance using Ohm’s law but to me this is a workaround.

Anyway, thanks for many examples regarding behavioral sources, without these I’d not have understood the basics!

@Alegom: There is a section for feature suggestions, but I’m afraid it would not make any sense to use it.

@Sancho_P

Yeah, I can see that... Due to the report delivery date, I was forced to figured out a way. I decided to use another component (a current source, for example) and then photoshop the Omega instead of the arrow. Nothing a little creativity can't fix.

Thank you both for your help. Let's hope the forum moderators come back to life someday. ;)

@Sancho_P,

"There is a behavioral voltage and current source, but no “behavioral” resistance source."

For info:

:)

@Sancho_P,

" CL is not the fully fledged electronics simulator, but on the contrary, it is a very useful tool for beginners (like me) in simulation. It is ideal also for beginners in electronics "

Your words: my emphasis.

;)

I think you are confusing yourself over a tool for drawing schematics and a tool for simulating them.

If you just want to draw an Ohmmeter in your circuit diagram rather than simulate the actual operation of one in a circuit then you can use the CL Custom Part.

I have added an Ohmmeter symbol created this way to:

It does nothing but can be added to a drawing to indicate the presence of an Ohmmeter.

You can copy and paste it into your own circuits as required.

(I know that is too late for @Alegom).

An Ohmmeter is basically just a voltage source with an ammeter in series with it.

You cannot normally use an Ohmmeter in a circuit with the power applied to it. You get nonsense readings because then the voltage source in the Ohmmeter is no longer the only voltage source driving currents around the circuit so the current in the Ohmmeter internal ammeter is no longer controlled by the Ohmmeter internal voltage source.

The resistance measurement techniques described in my example are applicable to circuits that do have power applied. As such they represent very powerful tools that have no simple real world equivalent.

Using behavioural techniques like these it is possible to make measurements such as the slope resistance of diodes under varying forward bias. Such measurements cannot be made with a simple Ohmmeter.

For the reason I have just described, Ohmmeters are of limited use in a simulator and you do not normally find Ohmmeter symbols and functions for them.

TINA (and TINA-TI) from DesignSoft and Multisim from NI are exceptions rather than the rule.

If you need to measure resistance in a circuit to solve some sort of educational task such as a general resistor network then you need the resistors connected up and then you apply a known voltage across some pair of nodes and then measure the current through that source to find the resistance. However, apart from the Ohmmeter, there is no power source in the circuit.

To do that in a simulator all you would do is set up a voltage source across the pair of nodes and then set up an expression to calculate the voltage of the source divided by the current drawn through it by the load. That is the resistance of the whole network.

This is OK for networks where the Ohmmeter is the sole power source.

However if you want to measure a resistance in a network with some other power source applied to it then you need to measure the dynamic resistance of a circuit.

If you need to measure some dynamic resistance - such as a the slope resistance of a zener diode or the on-resistance of a MOSFET or the output resistance of an opamp - then you need to use behavioural techniques based on measuring the voltage across a pair of nodes and the current through a specified branch. This is what my example shows.

Of course you can work the other way round by connecting a current source across a pair of nodes and then measure the voltage but the basic idea is the same.

All that aside, I agree that the documentation for CL could be better.

I'm sure the authors of CL would welcome any help in improving it.

:)

It's a shame that CL is closed source. If it was FOSS then the community could help improve and expand it.

@signality,

Nope, I don’t talk about simply “drawing a circuit” with such an icon and I know how to use an ohmmeter in electronics (e.g. that I have to disconnect power and maybe other parts first to get the reading I’m asking for).

I’m not really advocating the need of an Ohmmeter in this “virtual electronics” world maybe because I did not have the need so far.

But being far away from the theoretical side I can tell you from “real” world that my three multimeters don’t have a dial for volts and amps only. In the real world it is often recommended to measure first and then replace a component and restart … (but I think you know that ;-) ).

In the “virtual” world of course you don’t need that (which is a pity, as overload should be part of the game) - but it might be interesting to check the DC resistance as a part of the design process, I mean to apply two probes and read the value in OHMs, not to use a workaround and calculate. I mean even before thinking about the simulation. That might be interesting for educational purposes, too.

Again, I’m not really advocating …

Just wonder “why not?”.

;-)

And … sorry to say but I have to laugh …

… why oh why should I use a voltage controlled current source with LIMIT() and ABS() when I only want to use an expression within a resistor’s value? These items are a bit beyond my horizon and I guess beyond an electronic - beginner’s horizon, too.

• Let alone it destroys the esthetics of a diagram. It is not the solution but the problem.

[cough] Please take into account that I live far down in Spain and my blood is boiling quickly (we still had 31 °C today). Never take me serious and never ever personally insulting. If I do then I don’t know about, but I apologize anyway in advance!

Regards, Sancho

BTW: “… then the community could help improve …” ??? But you DO !!!