LM3914 Issues with direction

Hello guys :)

I've recently been messing with PWM and this LED bargraph driver to be able to use 8 of them for a certain project I want to do. I got over the first few hurdles with it, which were mostly fixed by adding a RC filter between the PWM pin and the signal input.

Here's a video: https://www.youtube.com/watch?v=dldXSlcuJic

Here's the schematic:http://i.imgur.com/kNOFVlP.jpg *note the diodes on there at the top are actually LEDs yes and the bottom two resistors are both 3k9

The datasheet: http://www.ti.com/lit/ds/symlink/lm3914.pdf

The problem is pretty self explanatory from the video: It shouldn't be going two ways and I'm not sure why it does! Can anybody shed some light on this?

Thank you in advance!

Are you trying to fiddle with (customize) the range?

What if you have just your 1k2 from 6&7 to Gnd and pin 8 straight to Gnd? Can't see your breadboarding in detail from the youtube.

(I put a 1k in parallel with the pin1 LED, they always seem to be faintly on otherwise.)

Well, for 64 LEDs, it would be much easier to use a single MAX7219. Two of them for up to 128 LEDs. Three Arduino pins to control as many as you want.


And the easiest (and cheapest) way to use a MAX7219 for this sort of project, is to buy one of the matrix module kits from eBay, assemble the PCB but instead of fitting the sockets for the LED matrix, connect your LED wiring to those positions on the PCB.

The LED modules you are presently using will work just fine with this.

This card I offer does just that, with 2 connections per LED to make it really easy. http://www.crossroadsfencing.com/BobuinoRev17/ |500x374

Do those sockets mate sufficiently well end-to-end that you can plug in a 32-way IDE plug (or header pins to mate with a recycled - actually 34-way - floppy cable)?

I would hope so, as I think the OP wants all the LEDs in one line - or perhaps others may!

Hi again, thanks for the replies!

The 8 bargraphs will not be driven together they will be separate displays for different parameters. My issue is that the

I tried changing both resistors to 10k trimpots to see what effect changing the resistor values would have on the circuit but I'm still getting the display switching directions on every pulse which is what i'm trying to avoid!

any more suggestions?

Septagon: I tried changing both resistors to 10k trimpots to see what effect changing the resistor values would have on the circuit but I'm still getting the display switching directions on every pulse which is what i'm trying to avoid!

any more suggestions?

I asked you to do a simple thing and you replied about some other thing. I have nothing further.

When the pot substituted for the 3k9 resistor is turned down it does the same thing, i put the pots in to test it over a range of values. It works to keep it going in one direction, but it makes it sensitive to only a very small voltage range

I'm starting to think that the problem might be the non-brand LM3914 i have. I'll pass by my local place to get a nice texas instruments