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Old 10th August 2004, 12:59 AM   #1
imix500 is offline imix500  United States
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Default Help with this schematic?

Hello all, so I designed this circuit to hopefully be the solution to my thread about driving a bunch of leds. I've never worked with this chip in cascaded mode. Does it look ok? Thanks!
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Old 11th August 2004, 08:14 AM   #2
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Default display...

What is the expected output and what is the ic number,( LM391x )
Is it an extended range VU meter?
Why are you using all the Ref out? Your R HI are all at 1.2 volts.

Except the first ic, all others have no voltage across R hi and R lo, as both are tied at same potential.

Search for the ic datasheet on National site at www.national.com

Gajanan
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Old 11th August 2004, 09:12 AM   #3
imix500 is offline imix500  United States
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Hi gmphadte, Honestly, I just figured the resistors needed to be doubled as the cascade went on because the example on the data sheet did that- doubled the r value for the second chip. But that resistor sets the led drive current right? Then shouldn't they all be the same?
I figured this schematic wouldn't work because there are several points I don't get, this was just to start from since I have not been able to find a working circuit like this.
They are all 3914 -linear.
All I'm looking for is a circuit that will drive, in this case, 50 steps. This is not for any real measurement purpose, just a way to control 50 sequencial steps of leds with a control voltage.
I'm not settled on a max v in but 24v would be comfortable.
The data sheet only touched on using the chip in bar graph mode when cascaded- all examples except for one are in dot mode. So, I did a fair bit of guessing.
So my question really is how to set up each chip to respond to a range of input voltage i.e. 0-4.8v, 4.9-9.6v, 9.7-14.4v... I thought that was what using the ref out to drive the ref adj of the next chip did but I was only guessing there. Agian, it's what they did in the example. But I do see how they can all be at the same potential. Any help would be greatly appreciated.
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Old 11th August 2004, 10:13 AM   #4
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Default Bar graph display

The LED brigtness is controlled by the load on the Ref Out.

A simple solution would be...
you can set one Ref to 12 volt which is the max specified, load other REFs with whatever, cascade all dividers R LO to next chip's R HI, R LO to next chip's R HI and so on... making a long potential divider. For using 24 volt at the input, the chip will not be damaged as it is within safe limit but to read 24 volts, you will have scale/attenuate the i/p voltage

You don't need those 20 Ks at the LED.

Gajanan
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Old 11th August 2004, 11:08 AM   #5
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Default sequential LED in DOT mode

If you are not interested in voltage and only interested in DOT mode, then you should use 4017s in a tricky way.

This was the need in one timer and I wanted to indicate the step number by a glowing LED. The oscillator was made programmable using ICM7217. This is something like a programmable mechanical street light timer.

The trick...

Follow carefully
LED 9(at pin 11) is not connected in all 4017s

The pin 11 is utilised to disable the present chip though an EX-OR gate and enables the next through another EX-OR. One input of the first EX-OR ic is tied high(can be looped also). The EX-OR output goes to CE (pin 13).

tie all resets together and all clock pins together. Get your clock and reset with large fan-out

Pin 11 will go to one i/p of self EX-OR and one i/p of next EX-OR

You want them to come back and forth, then place the LEDs wherever you want.

LED No.1-No.50-2-49-3-48-4-...

Gajanan
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