The Project LED volume indicator circuit can be used in stereo amplifiers to indicate the balance level of volume. As the human ear is not much sensitive to differences in sound level, the LED volume indicator circuit indicates the difference in the sound level in any channel by means of LED.
Input to the circuit is taken from the output terminals of each channel. The output signals are rectified by diodes D1 and D2, which are further filtered by capacitors C1 and C2. A DC voltage is developed across the voltage dividers compromising R1, R2, and R9, R10.
Other volume indicator circuits posted in bestengineeringprojects.comÂ
When there is the same volume in both channels, the voltage at points A and B are equal and the voltage difference between points A and B is zero. So both transistors T1 and T2 remain cut–off. When the volume in the left channel is increased, the voltage at point A also increases. When the voltage at point A increases by about 0.6 volts more than the voltage at point B transistor T1 starts conducting and switches on the LED driving transistor T3 Transistor T2 remains cut-off.
Similarly, when the voltage at point B increases by about 0.6 volts more than that at point A, transistor T2 conducts lightning RIGHT LED. Left channel LED remains off. In this way, the respective channel LED lights up to indicate the rise in volume level.
PARTS LIST LED VOLUME INDICATOR CIRCUIT
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Resistors (all ¼-watt, ± 5% Carbon) |
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R1, R2, R9, R10 = 470 Ω/0.W R3, R8 = 10 KΩ R4, R7 = 22 KΩ R5, R6 = 680 Ω R11 = 33 Ω R12 = 68 Ω |
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Capacitors |
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C1, C2 = 220 µF, 40V (Electrolytic Capacitor) |
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Semiconductors |
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D1, D2 = OA91 (Germanium diode) T1, T2 = BC148B (general-purpose NPN bipolar junction transistor) T3, T4 = BC158BÂ (general-purpose PNP bipolar junction transistor) LED1, LED2 = 2 different color LEDs |
Germanium diode OA91 is out of production since long. So, I tried the circuit with 1N34 but the effect of “balance indication” was not satisfactory.
Any small signal diode having minimum of 100mA forward current, and reverse breakdown of 75 volts, can be used.