LM3914 Dot/Bar Mode

[eunikesa]

I am having this campus project using LM3914 for the display.
I used the circuit shown at it's datasheet, but it doesn't work the way I wanted.

When the Ref Vout is equal to 2V, it shows dot mode, but with precision. When the Ref Vout is not equal to 2V (e.g. 5V), it shows bar mode but the accuracy is faulty.

Ref Vout = 1.25 (1 + (R2/R1))

How can I turn the mode into bar without changing the Ref Vout?

Any suggestion? Thanks.

 

[Boncuk]

I guess you made a connection error in your circuit.

Dot/bar mode is changed at pin9 only.

Connected to +V the display is in bar mode. If it's unconnected the display is in dot mode.

Boncuk

 

[Neil.r]

A very helpful tool, by Eric Gibb's on his blog.

https://www.electro-tech-online.com/blogs/ericgibbs/136-single-dual-lm3914-v3-0-calculator.html

This may help, it helpped me with my project.

Neil

 

[eunikesa]

It means using the different resistor (which provides different V Ref Out) shouldn't affect the mode of the display, isn't it?

I've connected pin 3 to pin 9, it works. But it only won't work when the V Ref Out is 2V. Does V Ref Out affect the range of the bar and the mode as well? What is V Ref Out?

 

[Boncuk]

I suggest you use the simulation circuit and apply voltages according to your designed circuit.

You might also post your circuit schematic to have it checked by forum members.

Boncuk

 

[eunikesa]

I've used the LM3914 calculator and it works properly, thanks.

Now I have another issue. When tried to connect 2 bargraphs in a row, it works properly. But when I want to connect 4 bargraphs, it became short-circuited. I found out the problem was the jumper connecting pin 2 and pin 4 on the first LM3914. But without the jumper, all bargraphs will lit up by itself. How can I solve this?