Tutorials for Basic Electronics

Here are a few tutorials to help you learn Electronics from the scratch:

1. WIRED SPY BUG:

Circuit Diagram:

Description:

This spy bug circuit will help you to listen to a conversation without being noticed or simply when you want to spy on a person. The circuit is constructed using a Mic, an Amplifier and a Speaker. The device can be wired or wireless depending on the comfort of your design. The device is built around an OpAmp IC741. It consists of a NPN transistor Q1(2N222) and a PNP transistor Q2(2N2907) connected in Push-Pull configuration.

Working:

This circuit can be divided into three sections for better understanding. First part is the Receiver, which is built using an Electric Microphone (Mic) and a Resistor R1. The microphone converts the sound into electrical signal and R1 adjusts the sensitivity of the Mic. The resistor R2 serves as a volume control and capacitor C1 is used to remove the dc component of the signal.

Next comes the pre-amplifier stage which is built using the OpAmp IC741. The IC is wired as an Inverting amplifier and hence the input signal is passed through the inverting terminal of the IC. The positive terminal or the non-inverting terminal is biased using the voltage divider R3 and R4. The resistor R5 is used to provide the negative feedback to the Opamp which in turn controls the gain of the Opamp.

The final stage comes to the amplifier built using the transistors Q1 (2N222) and Q2 (2N2907). These transistors are connected in Push Pull configuration which implies that one of the transistors amplifies the positive half cycle of the input and the other amplifies the negative half cycle. Collectively, we obtain an amplified 180 degree out of phase signal from the amplifier. The signal is then passed through the capacitor C2 to filter out any dc components and then finally to the Speaker.

2. Electronic Eye:

Components Required:

Regulator 7805
Resistors: R1=100k ohm, R2= 1k ohm, R3=100 ohm, R4=220 ohm, R5=820 ohm
Capacitors: C1=10 micro-farad, C2= 1 micro-farad
Diodes: D1, D3, D4= 1N4007
LED Diode D2
Light dependent resistor LDR
Buzzer
Transistors Q1 and Q2= BC547

Working:

An electronic eye is a simple circuit which operates the buzzer when a shadow falls on it. Initially a 9V battery is connected to the diode D1 which is in forward biased condition. This diode protects the circuit form negative voltages by allowing the current to flow in only one direction. A regulator IC 7805 regulates the voltage to 5V at the output. The two capacitors used before and after the regulators eliminate the ripple voltage so a constant voltage can be produced.

Light dependent resistors have resistance in mega ohms when it is placed in dark producing logic high at the output and low resistance when placed in light i.e. logic low at the output. This output is received by op-amp which compares the two inputs and send output to the two transistors. The first transistor inverts the input and the second transistor drives the buzzer. The buzzer starts ringing when the logic is high and also the LED starts blinking.

Other Projects:

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