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LED bar graph that lights up as you turn up a potentiometer?

wsal

May 16, 2015
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May 16, 2015
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Hi everyone,
I want to build something like this:
for my guitar volume pedal - an LED indicator that follows the motion of the pedal (which is controlling a potentiometer).

I bought a little kit for a DIY sound/vu meter, which uses an LM3915. I thought I might figure out a way to make it happen by experimenting with that circuit, but it's just a bit beyond me.

The circuit has a pin for "In" and "Ground" to which you'd connect your audio signal. I guess I'm trying to find a way for the circuit to work instead being fed by 9V DC that is running through the pot (dual gang, so there's a spare set of pins) inside the pedal, and as you move the pedal and thus the pot, the current running into the circuit causes more or less LEDs to light.

Here's the circuit as it currently exists as a meter:

Is it do-able?

Cheers
Will
 

Harald Kapp

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Nov 17, 2011
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Hi Will, welcome to electronicspoint.

The basic setup for the LM3915 is shown in the datasheet page 1. Remove Q1 and the 100nF capacitor leading to pin 5 of the IC. Connect the wiper of the potentiometer to pin 5, the other ends of the potentiometer to 0V and 9V respectively.

Note that the LM3915 gives a logarithmic display (number of LEDs ON is logarithmically coupled to the voltage on pin 5).

[Mod Note ... Harald, I replaced your link with another one ... every time I tried your link it crashed the browser ... I changed the comment to page 1 check and see if you want to use that page or another one]
 
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wsal

May 16, 2015
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May 16, 2015
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Hi Harold, thanks for your response. I did as you suggested, but it's not working yet. Do i need to bridge any of the connections where I've removed q1 and the 100nf capacitor?

Edit: scratch that thought, it does work! Now how can I get the LEDs to track the full range of motion of the pot? At the moment they all switch on within a quarter of a turn or so.

Thanks!
 

Harald Kapp

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Add a voltage divider after the pot. If you can't calculate the required values from the datasheet, simply use a second pot(an trim-pot) from the main pot's wiper to ground to adjust the range.
 
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