# Current sensor

I am desgning a circuit(network), where i need to show the path traversed by the greater part of the current at each node, consecutively. using an ammeter (or voltmeter) in every branch (around 20) makes it too tedious. Will LEDs do the required work? But they would light up at all locations, though their intensity might be different, will it be detectable to the eye? what should be the typical values of current (differences) for it to get detectable?
is the any better (cheap) method?

thankyou.

## Answers and Replies

anorlunda
Staff Emeritus
I am desgning a circuit(network), where i need to show the path traversed by the greater part of the current at each node,
I need a picture to understand what you want to do.

You can use the upload button.

So you don't need to measure the current? You just have to detect it's presence? How about a small sense resistor at each node with an op amp? As in a simple comparator configuration. It will detect the direction of current flow as well.

The output of the op amp will be positive for a current in one direction and negative for current in the opposite direction. The op amp will latch for very small currents, however.

The output of the op amp will be positive for a current in one direction and negative for current in the opposite direction. The op amp will latch for very small currents, however.
Thank you for the suggestion,
But i need to "show" the path. some sort of a detectable illumination (or even numerical values would do, provided the path is shown instantaneously, not manually moving with meters) like, any person seeing the circuit should know where all the larger portion of the current from the required node flows.
Actually, the deeper requirement is to follow from the first node, the branch with more current, then the same follow-scheme at the node this branch comes across and so on : This is what i mean by "path".
Sorry couldnt phrase it properly the first time.

I need a picture to understand what you want to do.

You can use the upload button.

The deeper requirement is to follow from the first node, the branch with more current, then the same follow-scheme at the node this branch comes across and so on : This is what i mean by "path".
Sorry couldnt phrase it properly the first time.
Thus any person seeing should be able to tell the "path".
this is in an effect to test "shortest path problem", using current follows least resistive path.

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• path.png
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Could you just buy multiple op amps? They're cheap. Problem with leds is there is significant voltage drop across them provided they are forward biased. An op amp current sensor with small sense resistor will not affect your circuit. Very small voltage drop.

Could you just buy multiple op amps? They're cheap. Problem with leds is there is significant voltage drop across them provided they are forward biased. An op amp current sensor with small sense resistor will not affect your circuit. Very small voltage drop.

But what shall be the output of this opamp current sensor? In electrical form? Could you tell me how to make the path be "seen" then?

Yeah. It will be a voltage. You could even connect two leds to the output of the op amp with opposite polarity to tell if the current is positive or negative. One led will light up for a positive current in a branch and the other will light up for a negative current in the same branch.

The output of the opamps will drive the leds BTW. Just make sure you put a properly sized resistor in series with each led

The output of the opamps will drive the leds BTW. Just make sure you put a properly sized resistor in series with each led

Agreed. But will this arrangement help in enhancing the difference in brightness of LED glow (due to different current sensed)? Making it detectable to the eye?

Placing Hall-effect sensors on each current leg, and monitoring their outputs on a multi-trace oscilloscope might be helpful.

Placing Hall-effect sensors on each current leg, and monitoring their outputs on a multi-trace oscilloscope might be helpful.

You'll need permanent magnets though to generate a magnetic field. Hall sensors will not show a transverse voltage across the sensor unless there is a magnetic field present. This could work however.

The best way to actually measure relative currents would be to actually measure the output voltage of the op amps and display them somehow on a screen.

Check this reference out. http://www.eetimes.com/document.asp?doc_id=1279415

Sure is a good option,
thank you for your time.

I would use one of the amplifier based current sensors in the lin kthough instead of a comparator. The comparator will latch for very small currents.

Good luck!

jim hardy
Gold Member
Dearly Missed
leright is on the right track, i think....

How far do you want to go ?
There exist integrated circuits designed to measure current in a wire
search on "High Side Current Sense"
they include the differencing amplifier and deliver an output in proportion to current measured.
Some will even use a length of printed circuit trace or small wire as current sensor

http://www.mouser.com/new/semiconductors/amplifier-ics/current-sense-amplifiers/n-6o48g [Broken]

I suppose this is a hardware demonstrator of some sort ?

I'm old fashioned and would use galvanometers.
But recognizing that the eye detects motion quicker than it does intensity
and that these days computers do everything
it'd be a good Arduino or RaspberryPi project.....
behind the board , read the analog current signals into a program
and have it flash individual two-color LED's at rate and color determined by their respective current's magnitude and direction ?
Measurement points in series with one another , like 5-8 or 10-14, should flash in unison to drive home Kirchoff's Current Law.

Last edited by a moderator:
cnh1995
cnh1995
Homework Helper
Gold Member
it'd be a good Arduino or RaspberryPi project.....
I recently did a small project based on arduino which involved measurement of power system parameters like voltage, current, pf and power. I used a hall effect current sensor IC and it did a very good job. You get an output voltage proportional to the current and that voltage can be read by arduino and displayed on the screen.

I recently did a small project based on arduino which involved measurement of power system parameters like voltage, current, pf and power. I used a hall effect current sensor IC and it did a very good job. You get an output voltage proportional to the current and that voltage can be read by arduino and displayed on the screen.

As old tele man and cnh1995 mentioned, another possibility is a hall sensor. I believe you would need a magnet also in this type of sensor, but I think magnets are integrated into hall effect current sensors.

cnh1995
Homework Helper
Gold Member
I think magnets are integrated into hall effect current sensors.
Yes.

leright
I used the term "latch" above btw for the op amp suggestion. That was the wrong term I think, since when the current goes to zero the output will be zero. It won't actually latch (i.e. the output won't stay high when the input goes to zero).

Nidum
Gold Member
All resistors of known values . Test on node voltages .

Sampling wires connected to each node . A/D conversion . PC I/O . Calc currents . Graphics display .

Option live display of actual grid with (eg) colour coding for different current levels .

leright
Merlin3189
Homework Helper
Gold Member
Looking at your diagram it seems to me that you can calculate the current in each leg and the potential at each node.
So you could assemble the circuit on a white board and use a projector to place a computer generated image on top. This could be pictures of galvanometers, lights of varying brightness or colour, lines which grew in thickness according to the current, or whatever your imagination came up with.
You could either sense the voltage(s) applied (I can only see the battery, but there's no reason you couldn't attach other sources) to calculate the currents, or (IMO better) use computer controlled sources to apply whatever voltages you wanted to any nodes.
Of course you don't even need to build the circuit, just use an image of it.

If you must stick with hardware attached visibly to your circuit, the little galvanometers "hifi" manufacturers used to put as level displays were ridiculously cheap. Though if they're not used anymore, they may simply not be available.

jim hardy