Dark detector circuit using LDR, LED

This is a basic dark detector/sensor circuit diagram based on a Photo Resistor (LDR) and  few numbers of parts.

Parts list of dark detector:

R1 = 330Ω Resistor
R2 = 1KΩ Resistor
R3 = 1k Variable Resistor
Q1, Q2 = BC547 Transistor
One Photo Resistor (LDR)
One 6V DC power supply or Battery

Circuit diagram of dark detector/sensor:

Fig: Circuit diagram of dark detector/sensor

LED Sound level display circuit by using IC LM3915

This circuit is about audio sound level LED display, indicator, monitor or you can say it “Audio VU (Volume Unite) Meter”.
This is a simple audio sound level LED display circuit diagram. The circuit is completely  based on  a single ic LM3915 from National Semiconductor. The LM3915 is a monolithic integrated circuit. It displays the audio sound level in terms of 10 LEDs and providing a logarithmic 3 dB/step analog display.

Audio sound level display circuit diagram

Fig: Circuit diagram of sound level display using ic LM3915

The audio sound level LED display circuit can operate from a single supply 3V to 25V. But I  suggest to use 9-12V. LED brightness can be controlled with a single pot( variable resistor) as shown 10K ohm in the circuit. Connect the audio input signal in Pin-5 of LM3915 from output of a audio device like output of audio amplifier or any other source.

The Pin-9 of LM3915 is to select dot or bar mode display. To make the circuit moving dot display instead of a bar graph display disconnect the Pin-9 from +V.