Bench Amplifier Based on LM386

A small 325mW amplifier with a voltage gain of 200 that can be used as a bench amplifier, signal tracer or used to amplify the output from personal radios, etc.

 Circuit Diagram

Notes:
The circuit is based on the National Semiconductor LM386 amplifier. In the diagram above, the LM386 forms a complete non-inverting amplifier with voltage gain of x200.

A datasheet in PDF format can be downloaded from the National Semiconductor. The IC is available in an 8 pin DIL package and several versions are available; the LM386N-1 which has 325mW output into an 8 ohm load, the Lm386N-3 which has 700mW output and the LM386N-4 which offers 1000mW output. all versions work in this circuit.

The gain of the Lm386 can be controlled by the capacitor across pins 1 and 8. With the 10u cap shown above, voltage gain is 200, omitting this capacitor and the gain of the amplifier is 20.

The IC works from 4 to 12Volts DC, 12Volt being the maximum recommended value. The internal input impedance of the amplifier is 50K, this is shunted with a 22k log potentiometer so input impedance in this circuit will be lower at about 15k. The input is DC coupled so care must be taken not to amplify any DC from the preceeding circuit, otherwise the loudspeaker may be damaged. A coupling capacitor may included in series with the 22k control to prevent this from happening.

The Finished Circuit.

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Morning Alarm Circuit Diagram based LDR

This LDR based alarm can be used as get up alarm. The Alarm turns on in the morning automatically and turns off only when manually switched off ,so you will have to get up. It is a simple LDR based light sensor circuit.

LDR or Light Dependent Resistor is a kind of variable resistor and its resistance depends on the intensity of light falling on it. In complete dark, its resistance is as high as 1 Meg Ohm, but it reduces to 100 ohms or less in full light. So it is an ideal device to use as light switch. Sensitivity of LDR depends on its size also. Commonly available sizes are 3mm, 5mm, 10mm etc. But costly types with greater sensitivity are also available.

When the circuit is place in dark, near the window, LDR fails to conduct and T1 will not get base bias. So it remains off and buzzer will be silent. When the sunlight falls on LDR, IN the morning, LDR conducts and provides base bias to T1. T1 then conducts to activate the buzzer. Capacitor C1 is provided for the clean switching of T1. T1 will conduct only when C1 is charged fully. This prevents chirping sound during light transition.You can use an easily available Music buzzer to get melody tone.

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