Wiring Schematic Diagram

This is a delayed turn-on relay driver and can produce time delays for up to several minutes with reasonable accuracy. The 4001 CMOS gate here is configured as a simple digital inverter. Its output is fed to the base of a regular 2N3906 transistor, Q1, at the junction of resistor R5 and capacitor C2. The input to IC1 is taken from the junction of the time-controlled potential divider formed by R2 and C1. Before power is applied to the circuit, C1 is fully discharged. Therefore, the inverter input is grounded, and its output equals the positive supply rail; Q1 and RY1 are both off under this circuit condition. When power is applied to the circuit, C1 charges through R2, and the exponentially rising voltage is applied to the input of the CMOS inverter gate. After a time delay determined by the RC time constant values of C1 and R2, this voltage rises to the threshold value of the CMOS inverter gate.

The gate's output then falls toward zero volts and drives Q1 and relay RY1 'ON'. The relay then remains automatic turn-off relay driveron until power is removed from the circuit. When that occurs, capacitor C1 discharges rapidly through diode D1 and R1, completing the sequence. The time delay can be controlled by different values for C1 and R2. The delay is approximately 0.5 seconds for every µF as value for C1. The delay can further be made variable by replacing R2 with a fixed and a variable resistor equal to that of the value of R2. Taken the value for R2 of 680K, it would be a combination of 180K for the fixed resistor in series with a 500K variable trim pot. The fixed resistor is necessary.

This crcuit from:  www.sentex.net

Sound Activated relay. The relay remains dormant until the op-amp activates upon sound via the electret-microphone. The input stage is a regular off-the-shelf 741 operational amplifier and connected as a non-inverting follower audio amplifier. Gain is approximately 100 which you can raise by increasing the value of R2. The amplified signal is rectified and filtered via C3, D1/D2, and R4 to an acceptable DC level. Potentiometer R5 is used to set the audio level to a desired sensitivity value to activate the relay via transistor Q1. Diode D3 is mounted over the relay coil to absorb sparks. The op-amp configuration in this particular drawing needs a dual voltage power supply which can be made from two 9-volt batteries. 

This crcuit from:  www.sentex.net

Here is a circuit that allows you to control a relay in response to sound from a non-amplified sound source (computer, CD player, or my Digital Sound Recorder board).

This circuit accepts audio input from any non-amplified sound source and when the volume reaches a certain level, it actuates a relay. This relay can be used to switch another device (light bulb, etc.) on and off in sync with the volume of the input.

The circuit can work from any 5–12 VDC regulated power supply provided a relay with the suitable coil voltage is used. When you first connect the supply voltage to the sound activated switch circuit, the relay will be energised because of the effect of capacitor C2. Allow a few seconds for the relay to be switched off. You can increase or decrease the ‘on’ period by changing the value of C2. A higher value results in a longer ‘on’ period, and vice versa. Do not use a value greater than 47 μ F.

Biasing resistor R1 determines to a large extent the microphone sensitivity. An electret microphone usually has one internal FET inside which requires a bias voltage to operate. The optimum bias level for response to sound has to be found by trial and error.

This 19 LED VU Meter circuit was designed by two monolithic integrated circuits to measure the level of audio signals whose unit of measurement is known as volume unit. The circuit round the IC1 makes input adaptation and amplification with the trimmer TR1 [GAIN]. The circuit round the IC2 makes half-wave rectification of acoustic signal. With switch S1, we select the type of indication, that we will have from the LED. With the prices in resistances R6 and R7 that exists in the circuit, the level of signal, in the entry is 7.8V (gain of first stage IC1, is one), and the difference of level between the LED D10-11, should are 3 db. The positive department of supply, should have the possibility of giving more current, one and it is overloaded with the current of LED.

list componet

R1-2   : 10Kohm      C1   : 100uF/25V       D1-19 : LED 3 or 5mm any colour. 
R3-4   : 10Kohm      C2-5 : 10uF/25V        D20-21: 1N4148
R5-8-9 : 1Kohm       C3-4 : 100nF           IC1   : TL 072
R6     : 330Kohm     C6   : 1uF/25V         IC2   : LM3915
R7     : 62Kohm      S1   : mini Switch     IC3   : LM3916 
TR1:    47Kohm Trimmer   

This circuit is a very simple circuit-level indication, with 10 Led. LM3915 IC is used to control the led, as an indicator VU Meter. This circuit uses just one IC and a very few number of external components. It displays the audio level in terms of 10 LEDs. The input voltage can vary from 12V to 20V, but suggested voltage is 12V.

The LM3915 is a monolithic integrated circuit that senses analog voltage levels and drives ten LEDs. The whole display system can operate from a single supply as low as 3V or as high as 25V.

The IC contains an adjustable voltage reference and an accurate ten-step voltage divider. The high-impedance input buffer accepts signals down to ground and up to within 1.5V of the positive supply. Further, it needs no protection against inputs of ±35V. The input buffer drives 10 individual comparators referenced to the precision divider. Accuracy is typically better than 1 dB.