LED Bar Indicator

I'm not sure what you're trying to accomplish but to answer your first question:

can i use an LM3914 or LM3915 IC

the answer is, yes. These ICs are voltage input devices but it can be possible to use current if you drop the current through a resistor. Remember Ohm's Law? E=I×R

As for your second question, I can't quite grasp what you're asking but here goes.

A Pulse-Width-Modulation (PWM) signal has an ON-to-OFF ratio (also called duty-cycle) that can be varied. A PWM signal that is at 50% (equal ON and OFF times) will have a high current than a 25% (ON time is 25% of the ON plus OFF times) PWM signal.

To start with, LED bargraphs are run by comparators turning on successive LED's as input increases, whether the signal is voltage or current. A resistor is a current to voltage converter. That is, V = I * R. Basic electronics.

Next, PWM stands for Pulse Width Modulation. Frequency is constant and pulse width varies. PFM stands for Pulse Frequency Modulation. Pulse width is constant, and the frequency varies. PWM voltage varies from zero to 100 % of source voltage under ideal circumstances (no losses). The average voltage of a PWM signal is the width (time) of ON period to width (time) of Cycle period. That is, if the pulse frequency is 1 kHz, the cycle period is 1 / f = 1 mS. If the pulse width is 0.1 mS, and the source voltage is 10 V, then the output voltage average is 1 V. This implicitly tells something: The full source voltage is applied to the load for 0.1 mS, and zero volts is applied for 0.9 mS.

Current is what makes LED's vary in brightness, not the applied voltage, although the applied voltage does have a distinct effect on brightness when applied without restriction, because of the forward voltage characteristics on an LED. Look up a voltage versus current curve for an LED on the internet. You will notice that the forward current goes up rapidly once the "knee" is reached, whereas it goes up slowly in the curve at the "knee."

A high source voltage can burn up an LED with one pulse. If the source voltage is not too high to destroy an LED, then a PWM signal applied to an LED may make it appear to be varying in brightness to a human being because of the way a human's eye works.

Hope this either helps or makes you want to learn more about electronic devices.

All the answers you have are correct, but I have a feeling that the PWM signal might not be accepted directly by these voltage chips, which are truly excellent and easy to use in analog situations). maybe a small cap across the chip to smooth the signal might help, but the chip needs a smooth supply from elsewhere as a power source....

I feel that you need somehow to use a couple of diodes to take part of the drive signal, from across a low value resistor that is in series with the motor drive current, and rectify it, smooth it with a small capacitor and then use the LM391X chip to indicate the voltage. Notice I said voltage not current....

I have never done what you want to do exactly, but that would be an area I would start with if nobody else gives you a better idea.....

Of course an analog current meter would do all that and give a proper indication without any electronics at all (just one resistor!).......it would dither at the frequency of the PWM, but that would probably not be noticeable at all.......and it would indicate the "mean" of the current exactly!

An analog current meter is just an analog voltmeter and a low value series resistor (parallel to the meter) in a motor connection. If the motor is driven in both directions, use a center zero meter....the series resistor to be calculated so that maximum motor current deflects the meter fully....many circuits for this on the web as this is only simple electronics 101 so to say.....

I hope this helps you further....

The application of this is for a container handler, in particular a reach stacker which uses a telescopic boom to reach in 3 containers deep to pick them up, the maximum safe allowable weight they can pick up differs depending on where the boom is i.e. - fully extended out or in, fully lifted or lowered. parkers IQAN network system offers the ability to calculate this from various sensors and tranducers, and we can link this to an output with variable current so i want to make an LED bar display to show the operator what percentage of maximum capacity he is at, i hope this makes sense and explains what im trying to do.

Why not just buy one? Laurel Electronics, among others, makes 'em.