Here is High performance LM3914/LM3915 VU meter projects that widely popular can display with 20 LEDs on stereo or mono with 10 LEDs for all audio system.And can easily build and cheap you must happy when use it.
This electronic VU meter set is circuit that High performance and widely popular than 40 years.
This project is very easy, because use alone IC only and a few external components. The display system can drive directly LED up to 10 LEDs and display as light running is DOT or BAR as you want follows by Figure 1.
The working principle
Figure 1 Electronic VU meter circuit diagram by LM3914 and LM3915
The main in working of this circuit is LM3914N or IC LM3915N as suitable for your working. Which the external circuit is the same.
Let’s to build many VU Meter circuits with LM3914 ::
The difference of the two ICs is that:
1. LM3914N will display as amplitude of signal in Linear form.
2. LM3915N will display as amplitude of signal in Logarithm form.
Normally if use amplitude of sound signal we should use the LM3915N.
The input signal from power amplifier wil be entered through to Voltage Doubler circuit consists of C1, C2, D1, D2 to convert sound signal voltage to DC voltage and have amplitude are 2 times of the input signal. Then, insert single to input pin 5 of IC.
And next IC will compare the signal amplitude, to drive LEDs display follows amplitude of input signal as above.
The Mode selection in working of circuit. to display in Dot or Bar form. The ability do with connecting a switch to pin 9 of IC. Which if indiscreetly release the switch will display is bar form. But connected the switch to pin 9 together with a positive voltage, the circuit will display in the dot form immediately.
How to builds this projects.
First of all, makes the PCB layout in stereo or mono as you need. Secondly, solders all components into the PCB, as you see in Figure 2 (stereo form) and Figure 3 (Mono form). Caution: Polarity of LED must be placed correctly. If you reverse the polarity, the LED does not light.
The parts list
D1, D2—————–1N4148__ 75V 150mA Diodes
R1———————-10K Resistors 1/4W
R2———————-2.7K Resistors 1/4W
R3———————-3.9K Resistors 1/4W
C1, C2—————–1uF 50V electrolyte capacitors
C3———————-47uF 16V electrolyte capacitors