lm3914 help

Projects General Guidance
1

I am trying to make a 20 segment LED bar graph.

I am using the PWM output via an RC which gives a variable signal of 0-4.5v which is fine.

For some reason my first 10 segments dont light and the range is only shown on the 2nd 10 led's.

The guidance in the data sheet is a bit confusing.

Pls see attached.

Does anyone have a cct they know works?

Thanks

Capture.JPG

2

Capture.JPG
Sorry, but that is one seriously useless diagram.

Please post it again with a resolution of at least 1200, or in the format with which it was generated - presumably PDF.

Yeah, the datasheet is not too helpful.

This appears to be the correct diagram if you just make the switch selection fixed for the mode you want.
LM3914x2.png

LM3914x2.png
LM3914x2.png874×779 25.3 KB

3

Sorry, It came from a screen grab and the design software won't allow another save format.

I looked at the one you suppliued from the data sheet but it only works on a 2.4v scale and it isnt clear how to scale it to 4.5-5v which is what I need.

How can I rescale the input?

Thanks

4

kpg:
How can I rescale the input?

Resistive divider.

You need to determine from the LM3914 datasheet what the input impedance of two parallel LM3914s is and take that into account in determining the resistor values.

OK, I looked at various ways to do it. Just use a voltage divider of two 4k7 resistors if putting 9k across your voltage to be measured is OK. Two 47k resistors would probably be quite OK too.

5

Thanks Paul

Appreciate the help!

Kev