Night security light

Night security light

Description.

 Here is a simple circuit switches on a light around 2 hours after midnight, the time at which most of the robberies taking place.

This simple circuit is build around a CMOS IC 4060 to obtain the required timing. During day time the LDR has low resistance and keeps the pin 12 of the IC1 high, preventing the IC1 from oscillating. When it is dark the LDR resistance becomes high and the pin 12 of IC1 becomes low and the IC starts oscillating, which indicated by the flashing of LED D3.The values of the timing components R1, R2, C4 are so selected that the out put pin3 of IC1 goes high after 8 hours. That means the high output drives the triac to switch on the lamp around 2’O clock. At morning, the LDR resistance drops and the pin 12 of IC1 goes high and stops the oscillation, making the lamp OFF. The switch S1 can be used to manually ON the lamp. The capacitor C2 prevents false triggering.

Circuit diagram with Parts list.





Notes.

•  Assemble the circuit on a good quality PCB or common board.
• The LDR can be general purpose LDR.
• The light sensitivity can be adjusted using the preset R6.
• The IC1 must be mounted on an IC holder.

Audio monitoring system

Audio monitoring system

Description.
Here is the circuit schematic of a simple audio surveillance system in which the transmitter will pickup sound from one location and the receiver at other location will reproduce it. The receiver and transmitter are connected by only one set of wire. Here both power supply and transmitted signal share the same wire.

The audio signals picked up by the microphone will be amplified by the double stage amplifier build around transistors Q1 and Q2.The POT R2 controls gain of the amplifier. The power supply for this circuit is drawn from the interconnection lines itself. The capacitor C4 bypasses all audio frequencies & noise from the line and ensures pure DC for the circuit. The output of the amplifier (audio signal) is coupled to the line via the capacitor C6.

At the receiver end the capacitor C7 extracts the audio signal from the line and feds it to the inverting input of IC1 (TL071) which is wired as a voltage amplifier. Output of IC1 is given to the input of IC2 (LM386) which is a integrated power amplifier.IC2 provided necessary current gain to drive the speaker. The POT R14 can be used control the gain of receiver. Capacitor C11 isolates audio frequencies and noise from the power supply of both the ICs.

Circuit diagram with Parts list.






Notes.

• Assemble the circuit on a general purpose PCB.
• Terminal A must be connected to A’ using the wire of required length. Do the same with B, B’.
• The microphone M1 can be a general purpose one.
• The speaker k1 can be 8 Ohm/2 Watt.
• POT R2 can be used to control gain of the transmitter.
• POT R14 can be used to control gain of the receiver.
• The circuit can be powered from a 12V battery or 12V DC power supply.
• IC1 and IC2 must be mounted on holders.

100W MOSFET power amplifier

  100W MOSFET power amplifier

A 100W MOSFET power amplifier circuit based on IRFP240 and IRFP9240 MOSFETs is shown here. The amplifier operates from a +45/-45 V DC dual supply and can deliver 100 watt rms into an 8 ohm speaker and 160 watt rms into a 4 ohm speaker. This Hi-Fi amplifier circuit is suitable for a lot applications like general purpose amplifier, guitar amplifier, keyboard amplifier. The amplifier can be also used as a sub woofer amplifier but a subwoofer filter stage has to be added before the input stage. The amplifier has a low distortion of 0.1%, a damping factor greater than 200, input sensitivity of 1.2V and the bandwidth is from 4Hz to 4 KHz.

Circuit diagram.

100W mosfet power amplifier circuit

About the circuit.

Capacitor C8 is the input DC decoupling capacitor which blocks DC voltage if any from the input source. IF unblocked, this DC voltage will alter the bias setting s of the succeeding stages. Resistor R20 limits the input current to Q1 C7 bypasses any high frequency noise from the input. Transistor Q1 and Q2 forms the input differential pair and the constant current source circuit built around Q9 and Q10 sources 1mA. Preset R1 is used for adjusting the voltage at the output of the amplifier. Resistors R3 and R2 sets the gain of the amplifier. The second differential stage is formed by transistors Q3 and Q6 while transistors Q4 and Q5 forms a current mirror which makes the second differential pair to drain an identical current. This is done in order to improve linearity and gain. Power amplification stage based on Q7 and Q8 which operates in the class AB mode. Preset R8 can be used for adjusting the quiescent current of the amplifier. The network comprising of capacitor C3 and resistor R19 improves high frequency stability and prevents the chance of oscillation. F1 and F2 are safety fuses.

Circuit setup.

Set R1 at midpoint before powering up and then adjust it slowly in order to get a minimum voltage (less than 50mV0 at the output. Next step is setting up the quiescent current and keep the preset R8 in minimum resistance and connect a multimeter across points marked X & Y in the circuit diagram. Now adjust R8 so that the multimeter reads 16.5mV which corresponds to 50mA quiescent current.

Notes.

• Assemble the circuit on a good quality PCB.
• Use a +45/-45 V DC, 3A dual supply for powering the circuit.
• Power supply voltage must not exceed +55/-55 V DC.
• Before connecting the speaker, check the zero signal output voltage of the amplifier and in any case it should not be higher than 50mV. If it is higher than 50mV, check the circuit for any error. Replacing Q1, Q2 with another set could also solve the problem.
• Fit Q7 and Q8 to a 2°C/W heat sink. Both Q7 and Q8 must be isolated from the heat sink using mica sheets. Heat sink mounting kits for almost all power transistors/ MOSFETs of almost all package styles are readily available in the market.
• All resistors other than R10, R11 and R19 are 1/4 watt metal film resistors. R10 and R11 are 5W wire wound type while R19 is a 3W wire wound type.

Power supply for the 100W MOSFET power amplifier.

+45 / -45 dual supply for the 100W mosfet power amplifier

A basic dual power supply is used for the amplifier circuit. If 6A ampere bridge is not available, then make one using four 6A6 diodes.C10 and C11 are high frequency bypass capacitors. Filter capacitors C8 and C9 must be at least 10000uF, higher the value lesser the ripple. Optional 3A fuses can be added to the +45 and -45 lines. Transformer T1 can be a 230V primary, 35-0-35 V secondary, 300VA step down transformer.

TDA7294 100W Audio Amplifier

TDA7294 100W Audio Amplifier

100W Audio Amplifier TDA7294.

TDA7294 is an integrated, monolithic, Class AB audio amplifier designed specifically for Hi-Fi applications. The IC has a DMOS output stage and can deliver 100W RMS into an 8Ohm speaker at +/-38V dual supply. The TDA7294 has low noise, low distortion, good ripple rejection and can be operated from a wide range of supply voltages. The IC has built in short circuit protection and thermal shutdown circuitries. The IC is available in multiwatt 15V and multiwatt 15H packages.

Description.

In the circuit TDA7294 is configured to provide 100W output power into an 8Ohm loudspeaker at +/- 38V supply. C8 is the input coupling capacitor and the input is applied to the non-inverting input (Pin3) of the IC. C3 and C9 are power supply filter capacitors while C10 and C4 are bypass capacitors. C2 is the bootstrap capacitor. RC network comprising of R1 and C1 improves the high frequency stability of the amplifier and also prevents oscillations. R2 and C6 sets the mute time constant while R3 and C5 sets the standby time constant. S1 and the mute switch and S2 are the standby switch. R5 is the input resistance and the amplifiers input impedance has a direct relationship to its value. R4 and R6 is used for setting type closed loop gain and with the used value, gain is 30dB. C2 is a feedback capacitor and it also provides DC decoupling.

Circuit Diagram.

TDA7294 100W amplifier

Notes.

• The supply voltage range is +/- 10V to =/-40V DC.
• Heat sink is required and its thermal resistance should be around 0.038 degree Celsius/Watt.
• Use an 8 Ohm 150W speaker as the load.
• For 100W output the supply voltage must be +/-38VDC.
• The power supply must be well filtered and free of ripples.
• If ripples are present in the power supply it may cause oscillations.
• VM = 1.5V is the mute ON threshold and VM=3.5V is the mute OFF threshold.
• VSTBY = 1.5V is the standby on threshold and VSTBY = 3.5V is the standby OFF threshold.
• Typical input resistance of TDA7294 is 100KiloOhm.
• Frequency response is 20Hz to 20KHz.
• 145 degree Celsius is the threshold for thermal shutdown. Slew rate of TDA7294 is 10V/microsecond and the open loop voltage gain is 80 dB.
• Quiescent current of TDA7294 is approximately 30mA and its maximum value is 65mA.

60 watt amplifier circuit

60 watt amplifier STK4038.

STK4038 is an integrated AF power amplifier that can deliver 60 watts of output power into a 4 ohm load. The internal fixed current circuitry reduces switch ON/OFF clicks. The IC supports the addition of external circuits for thermal shutdown, pop noise reduction, output short circuit protection etc.

Description.

The 60 watt amplifier shown below is designed based on the datasheet and performs very well. Capacitor C1 is the input DC decoupling capacitor which blocks any DC level present in the audio input and C12 is the input by-pass capacitor. R1 is the input resistor.C10 and C8 are the ripple filter capacitors for the positive and negative power supply rails. R9 and R7 are the current limiting resistors for the internal driver stage while C11 and C3 are their corresponding filter capacitors. Resistor R6 feeds back a portion of the output signal to the inverting input (pin2). Gain of the amplifier depends on the value of R6. C9 and R2 forms a Zobel network which improves the high frequency stability of the amplifier.

Circuit diagram.

60 watt amplifier circuit

Notes.

• A good quality PCB improves the performance of the circuit.
• Maximum supply voltage for STK4038 is +/- 57V DC.
• K1 is a 4 ohm / 75 watt loud speaker.
• While using 4 ohm speaker as the load, the power supply must not exceed +/- 32V DC.

Audio oscillator circuit

Audio oscillator circuit

ICL 8038 waveform generator.

ICL8038 is a monolithic waveform generator IC that can produce sine, square and triangular waveforms with very little distortion. The frequency can be programmed from 0.001Hz to 300 KHz using external timing capacitor and resistor. Frequency modulation and sweeping can be attained by using an external voltage. Other features of the ICL8038 are high linearity, high level outputs, simultaneous sine, square, triangle wave outputs, low external parts count, high temperature stability etc.

The working of ICL8038 is as follows. The external timing capacitor (C2 in the circuit diagram) is charged and discharged using two internal current sources. The first current source is on all the time and second current is switched ON and OFF using a flip-flop. Suppose the second current source is OFF and the first current source is ON, then the capacitor C2 will be charged with a continuous current (i) and the voltage across C2 increases linearly with time. When the voltage reaches 2/3 supply voltage, controlling flip flop is triggered and the first current source is activated. This current source carries double the current (2i) making the capacitor C2 is discharged with a current i and the voltage across it drops linearly with time. When this voltage reaches 1/3 supply voltage, the flip flop is resetted to the initial condition and the cycle is repeated again.

Circuit diagram – ICL8038 audio oscillator.

  

Audio oscillator circuit

The circuit diagram given above shows a variable audio frequency oscillator using ICL8038. Such a circuit is very useful while testing audio related projects. The frequency range of this circuit is 20Hz to 20KHz. POT R6 can be used for adjusting the frequency while POT R9 can be used for adjusting the distortion. POT R4 can be used for adjusting the duty cycle while POT R7 can be used for nullifying the variations in duty cycle. C2 is the external timing capacitor and R5 is  a pull up resistor.

Notes.

• The circuit can be assembled on a vero board.
• Use +10 /-10V DC dual supply for powering the circuit.
• The power supply must be well regulated and filtered.
• All fixed resistors are rated ¼ W.

Low cost fire alarm circuit

Low cost fire alarm circuit.

Description.

When there is a fire breakout in the room the temperature increases. This ultra compact and low cost fire alarm senses fire breakout based on this fact.
Transistor BC177 (Q1) is used as the fire sensor here. When the temperature increases the leakage current of this transistor also increases. The circuit is designed so that when there is an increase in the leakage current of Q1, transistor Q2 will get biased. As a result when there is a fire breakout the transistor Q2 will be on. The emitter of Q2 (BC 108) is connected to the base of Q3(AC 128). So when Q2 is ON Q3 will be also ON. The transistor Q3 drives the relay which is used to drive the load ie,light,bell,horn etc as an indication of the fire. The diode D1 is used as a free wheeling diode to protect it from back EMF generated when relay is switched.

Circuit diagram with Parts list.



Notes.

• The Preset R1 can be used to desired temperature level for setting the alarm ON.
• This is not a latching alarm,that is;when the temperature in the vicinity of the sensor decreases below the set point the alarm stops.
• The circuit can be powered using  a 9V battery or a 9V battery eliminator.
• All capacitors are electrolytic and must be rated at least 10V.
• The load can be connected through the C,NC,NO points of the relay according to your need.
• The calibration can be done using a soldering iron, and a thermo meter. Switch ON the power supply.Keep the tip of soldering iron near to the Q1. Same time also keep the thermometer close to it. When the temperature reaches your desired value adjust R1 so that relay gets ON.Done!