This electronic VU-meter is designed for who want to have a circuit that can drive LED up to 20 pcs.(Stereo 40 LEDs) Which the circuit using a generally IC will can not directly connect to uses.
In addition to this project is very easily circuit and also can modify to drives Solid State Relays for easily control a larger lamp. As you see complete circuit of the projects in Figure 1.
The working of this circuit.
A input signal form power amplifier is passed through to VR1, to adjusted the amplitude of this input signal in proper level.
Then, the signal is send to the voltage doubler rectifier circuit that consists of C1, C2, D1, D2 to the circuit. All transistor Q1-Q10 that together into the voltage compare circuit.
Can see that bass circuits of each transistor will be set a bias with D3-D40 provided to have voltage bias is different for each 2 volts, respectively.
Thus, transistor Q1 will start work at lower signal and Q20 will work on the strongest signal.
The section of circuit is in the dash as the shortening of the the circuit is repeated. Consisting of Q4-Q18.
How to Build this projects.
We Assembly the circuit on to PCB lay as Figure 2 correctly. So must be extra careful is. Devices with terminals such as Diode , Electrolytic capacitors and LED will are connected match terminals only.
Figure 2 the PCB layout and the components layout of the 20 LED cheap electronic VU-meter using transistor project
When assembly is completed, then to test to provided the voltage power supply to this project. While connects the input signal from speaker of power amplifier and next turn on it at highest audio, then adjust VR1 to LED glow fully all LED . Now already have fun.
The components List
Q1-Q20——————–2SC828,C945,C1815___45V 100mA NPN Transistor
D1-D40——————–1N4148___75V 150mA Diodes
R1-R20——————–15K___Resistors 1/4W +/- 5%
C1————————–33uF 50V___Electrolytic capacitor
C2————————–3.3uF 50V___Electrolytic capacitor
L1-L20——————–LED 2 x 5 mm.