Making a VU meter, need some help.

[unclesam93]

I've attached the schematic. It calls for 9 volts but I couldn't find a breadboard power supply for anything more than an adjustable 3.3 and 5 volts. Will this still work? Also, if it does work, will I have to change the resistor and cap values?

 

[audioguru]

The minimum supply voltage for the LM386 is 4V. The LM3916 circuit is wrong because the value of R4 sets the LED current at only about 0.6mA each which is very dim. If R4 is changed to 560 ohms then the LED current is 18mA which is nice and bright.

The display will be a dim blur because the circuit is missing the peak detector circuit shown in the datasheet of the LM3915. It recommends setting the IC to the DOT mode when the peak detector circuit is not used.

 

[unclesam93]

So I don't NEED 9 volts? And I'm sorry, I'm still learning, I don't know know what you mean with the peak detector circuit. What would I have to change? And instead of using the mic, could I just use an audio jack?

 

[audioguru]

Why don't you read datasheets?
The LM3916 works from a supply that is from 3.0V to 25V but it gets too hot when the supply voltage is high and the LEDs current is high.

The datasheet for the LM3915 has three peak detector circuits and explains them.

The microphone has a very small signal level which is amplified 200 times by the LM386 amplifier used as a preamp. You can use an audio jack for a microphone or use the jack to feed a line level signal to a volume control (if needed) that feeds directly into the input of the LM3916 without using the LM386 preamp. Then do not use R1 that is used to power an electret mic.