LM3914 Problems

**tvsound** · 14th March 2009 07:21 PM

Hi,

I am trying to build a circuit that has 3 cascading LM3914 chips driving 30 leds in dot mode and am encountering the following problem...

When the signal input is above the V-Hi reference level the top led of each chip stays on.

So...even though the "bargraph" does what I want...ie, as the signal voltage drops the leds go from "top" (led 1) to "bottom" (led 30) when the signal voltage is at it's highest (in this instance 1.25V) as well as led No.1 being on (which I want) led No.11 & LED No. 21 are also on.

I can see that if I was running this in "bar" mode it wouldn't be a problem but I really need to run this in "dot" mode.

Any Suggestions???...I am currently copying the circuit out of the NS datasheet onto a breadboard and am fairly sure I am not making any mistakes.

Please feel free to enlighten me...and as I am very dim and a newbie at electronics please feel free to make your answers as basic as you wish!!!!...and if you want to include a circuit diagram that would be great!!!

Kind Regards
TVSound:

**Sceadwian** · 14th March 2009 07:30 PM

Additional wiring is required for the dot mode to work properly while the chip is cascaded, it's fully covered in the PDF data file how you need to hook them up. It's relativly simple, it requires as 10 or 20k resistor and a few lines from each chip to be hooked up in a certain way.