Hello,
I have in plan to build an vu meter with 30 leds in tototal 2 channel by 15 led. Audio input i will take from 3.5mm jack and send it to an analog pin of Arduino. But arduino doesn't have 30 pins to cover all leds. I can do a vu meter with 12 Led.

I have this materials.
Arduino UNO, Nano
1xSN74HC595N
1xMAX7219CNG
CD74HC4051E

 

You could use the 74HC595 to get 8 bits of output from 3 arduino pins - might be able to do it with 2 pins.
With four of them you could convert 12 arduino pins to 32 output bits.

 

You can add more 74HC595’s in series to get 32 LED’s.

 

Look up multiplex.

I built a scrolling LED display that controls 35 LEDS in 5x7 matrix with 9 I/O's. Could have used fewer, but I have 40 I/O's available and using 7 to drive the rows simplified the hardware.

 

This one uses a PIC but it could give you some ideas: https://s-o.webnode.cz/vu-metr/
Cheers, E

 

Thanks for your suggestions. With what i see using LM3915 is the best and simple option than mess with arduino and shift registers.

 

Look up multiplex.

I built a scrolling LED display that controls 35 LEDS in 5x7 matrix with 9 I/O's. Could have used fewer, but I have 40 I/O's available and using 7 to drive the rows simplified the hardware.

What a bout a matrix with 2x15 can be done?

 

What a bout a matrix with 2x15 can be done?

With sufficient hardware, you could do it with 2 pins.

 

15 x 2 would use 17 pins.
6 x 5 would use 11 pins.

Bob

 

15 x 2 would use 17 pins.
6 x 5 would use 11 pins.

Bob

Add an inverter, and you eliminate one pin for 15 x 2, making a total of 16 pins.

 

You don't need extra hardware. You can do it with 12 pins.

 

You don't need extra hardware. You can do it with 12 pins.

Presumably will need 'column' transistors if multiplexing?

 

Presumably will need 'column' transistors if multiplexing?

No. I have done 4-digit 7-segment displays without using driver transistors.