Voltage to dot graph,overlap problem

[Screech]

So, I have a Voltage to dot graph,overlap problem.

I'm just using the LM3914 voltage to bargraph driver in dot mode.

How do I eliminate the slight over lap problem, as one led turns off as another just starts to turn on.
The overlap is at .1 volt(datsheet) overlap.

I never want two leds to be on at the same time, even if they are on for a thousanth of a second.



Hope you guys can help :?
Thanks

 

[Screech]

oops
the overlap is 1mv (datasheet).

hopefully all will be ok. :?

 

[pike]

I think you may have it set in "bar" mode and not "dot" mode. Pin 9 should be left open circuited for this to happen.

Bar mode is usually used in audio applications, that shows the voltage of the output of the amplifier, but a '3915 is used (log type). '3914 is the linear type.

 

[Screech]

Mike, It's in dot mode. No doublts about it.
I have used both modes, but it's the dot mode I will be using.
And yes, it's the linear one i want too.
It's just the overlap that concerns me.
I'll cross my fingers.
Thank anyway.

 

[ljcox]

What you need is a small amount of hystersis.

This could be done by positive feed back to the input, ie. a resistor from each output to the input.

In order to confirm the feasibility of this idea and, if feasible, calculate the resistor values, you will have to look at the data sheet for the IC. If you can't do it, I'll help.

Len

 

[Screech]

ljcox,I will get back to you on that in the future.
I Will build the circuit first, then
All Depands if the circuit with work fine with the 1millivolt overlap.
If not, Iwill get back to you.
Thanks.
Must watch the Grandprix now.
I'm in Melbourne too.

 

[ljcox]

If, after testing, you need further help, post your circuit and I'll do the calculations for you.

Len

 

[Screech]

Will do.

Thanks mate

 

[ljcox]

Screech,
I looked at the National Semiconductor data sheet of the LM3914.

On page 12, it has a circuit showing how to add hystersis.

Len

 

[Screech]

Yeah, I just had a look.
But it says it's for bar mode only.
I'm using dot mode.

Also from the datasheet:
The display driver does not have built-in hysteresis so that
the display does not jump instantly from one LED to the next.
Under rapidly changing signal conditions, this cuts down
high frequency noise and often an annoying flicker. An overlap
is built in so that at no time between segments are all
LEDs completely OFF in the dot mode . Generally 1 LED
fades in while the other fades out over a mV or more of
range (Note 3). The change may be much more rapid between
LED No. 10 of one device and LED No. 1 of a second
device chained to the first.


Len, don't worry about it for now.
I'll see how I go.

Thanks.
Screech

 

[ljcox]

It should be possible to do it for the dot mode also. Let me know if you want to proceed.

Len

 

[Screech]

Len, that's excellent, that you can do it.

You are a champ!
Give me about a week, then I'll let you know if it neads to be done.

Screech