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bipolar bar graph driver? for +/-10V

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danjel

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I want to make a 20 segment LED bargraph for displaying a voltage source with a range of -10 to 10V.

Brief searches show the LM3916 as a common device (I would need two chained) but it also appears to be obsolete at mouser. What is the modern replacement?

Any good strategies for this simple task?
 
just clarify, this graph should be bipolar so that OV is displayed as a bar in the middle, positive would be a bar in the top half and negative would be a bar in the bottom half.
 
The LM3916 was an audio VU meter that you do not want. You want LM3914 ICs that are linear voltmeters.
 
The LM3916 was an audio VU meter that you do not want. You want LM3914 ICs that are linear voltmeters.

You are totally right. I looked at the LM3914 app notes and I think there is even an example of using two led bar displays with two ICs and the dot display centered.
 
Those bar graph driver chips are now getting very old, but may still be useful for a one off home hobby project..

The modern way to do it would be with a microcontroller that has an inbuilt analog to digital converter, and use that to drive a multiplexed array of LEDs.
 
Multiplexed LEDs are dim unless their momentary current is very high so many transistors or driver ICs are needed. The LM3914 has 10 LED drivers built-in.
 
The "Zero-Center Meter, 20 Segment" application schematic in the data sheet appears to do what you want. It uses an LM337 connected to a negative supply, which offsets the ground ≈-1.3V and allows circuit response to both positive and negative input signals.

Edit: You likely will have to attenuate the ±10V signal to be compatible with the sensitivity of the circuit input (which I think may be ±1V).
 
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The "Zero-Center Meter, 20 Segment" application schematic in the data sheet appears to do what you want. It uses an LM337 connected to a negative supply, which offsets the ground ≈-1.3V and allows circuit response to both positive and negative input signals.

Edit: You likely will have to attenuate the ±10V signal to be compatible with the sensitivity of the circuit input (which I think may be ±1V).

Thanks for the advice, I will give it a try. Why do you think it is ok to bias it down a volt but not 10? Another thing that strikes me as odd is the mode pin is tied to v+ in that example, which indicates bar mode instead of dot, which would be odd for bipolar operation (they would light down to the ground indicator at all times?). I dont understand this circuit, but I'll give it a shot. Do you think they are using a negative regulator because this voltage needs to be highly stable, or could I use a voltage divider from my -15 line?

Thanks again,
Cooper
 
You might be able to bias it to -10V, but it could over-stress the device. You'd have to calculate all the pin voltages under those conditions to see if any are over the voltage limit.

I do believe the negative regulator is for stability.
 
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