Electronics World

Simple Security System

noreply@blogger.com (Albin George) — Tue, 29 Nov 2011 03:21:00 +0000

You can use this simple and reliable security system as a watchdog by installing the sensing loops around your building. You have to stretch the loop wires two feet above the ground to sense the unauthorised entry into your premises. Wire loops 1, 2 and 4 are connected to the A, B and C inputs of 7-segment decoder 4511 (IC1), respectively, while the D input of IC1 is grounded permanently.The loops are also connected to a dual 3-input NOR gate and inverter CD4000 (IC2) to activate the alarm. Fig. 1 shows the circuit of the digital security system, while Fig. 2 shows the proposed wiring diagram for the loops around the premises. Before using this security system, make sure that loops shown in Fig. 2 are connected as shown in Fig. 1. If you don’t want to use a buzzer, switch it off by opening switch S2. The circuit works off a 9V regulated power supply.

However, battery back-up is recommended. A commoncathode, 7-segment display (LTS543) is used for displaying whether the loops are intact or not. If loop 1 is broken, the display will show ‘1’. If two or all the three loops are broken, the display will show the sum of the respective broken loop numbers. For example, if loops 1 and 4 are broken, the display will show 5(1+4).

When all the three loops are intact, the display will show ‘0.’ All the three inputs of gate N1 remain low to give a high output. This high output is further given to gate N2 and, as a result, its output remains low. This keeps transistor T1 in cut-off position and the piezobuzzer does not sound. When any loop is broken, the output of NOR gate N1 goes low, while the output of gate N2 goes high. Transistor T1 conducts and the buzzer sounds to alert you. You can mute the buzzer by switching off power to the circuit through switch S1.

Water Level Controller and motor Protector

noreply@blogger.com (Albin George) — Tue, 29 Nov 2011 03:14:00 +0000

Many a time we forget to switch off the motor pushing water into the overhead tank (OHT) in our households. As a result, water keeps overflowing until we notice the overflow and switch the pump off. As the OHT is usually kept on the topmost floor, it is cumbersome to go up frequently to check the water level in the OHT.

Here’s a microcontroller-based water level controller-cum-motor protector to solve this problem. It controls ‘on’ and ‘off’ conditions of the motor depending upon the level of water in the tank. The status is displayed on an LCD module. The circuit also protects the motor from high voltages, low voltages, fluctuations of mains power and dry running.

Circuit description:
Fig. 1 shows the circuit of the microcontroller-based water level controller and motor protector. It comprises operational amplifier LM324, microcontroller AT89C51, optocoupler PC817, regulator 7805, LCD module and a few discreet components.
The AT89C51 (IC2) is an 8-bit microcontroller with four ports ( 32 I/O lines), two 16-bit timers/counters, on-chip oscillator and clock circuitry. Eight pins of port-1 and three pins of
port-3 are interfaced with data and control lines of the LCD module. Pins P3.0, P3.1 and P3.6 are connected to RS (pin 4), R/W (pin 5) and E (pin 6) of the LCD, respectively. Pin EA (pin 31) is strapped to Vcc for internal program executions. Switch S2 is used for backlight of the LCD module.

Power-on-reset is achieved by connecting capacitor C8 and resistor R14 to pin 9 of the microcontroller. Switch S1 is used for manual reset.

The micro controller is operated with a 12MHz crystal. Port pins P2.0 through P2.2 are used to sense the water level, while pins P2.3 and P2.4 are used to sense the under-voltage and over-voltage, respectively. Pin P3.4 is used to control relay RL1 with the help of optocoupler IC3 and transistor T5 in the case of under-voltage, over-voltage and different water level conditions. Relay RL1 operates off a 12V supply. Using switch S3, you can manually switch on the motor.
The LM324 (IC1) is a quad operational amplifier (op-amp). Two of its op-amps are used as comparators to detect under- and over-voltage. In normal condition, output pin 7 of IC1 is low, making pin P2.3 of IC2 high. When the voltage at pin 6 of N1 goes below the set reference voltage at pin 5 (say, 170 volts), output pin 7 of N1 goes high. This high output makes pin P2.3 of IC2 low, which is sensed by the microcontroller and the LCD module shows ‘low voltage.’

In normal condition, pin 1 of N2 is high. When the voltage at pin 2 of N2 goes above the set voltage at pin 3, output pin 1 of N2 goes low. This low signal is sensed by the microcontroller and the LCD module shows ‘high voltage.’

Presets VR1 and VR2 are used for calibrating the circuit for under and over-voltage, respectively.

The AC mains is stepped down by transformer X1 to deliver a secondary output of 12V at 500 mA. The transformer output is rectified by a full wave bridge rectifier comprising diodes D5 through D8, filtered by capacitor C2, and used for the under and over-voltage detection circuitry.

The transformer output is also rectified by a full-wave bridge rectifier comprising diodes D1 through D4, filtered by capacitor C1 and regulated by IC4 to deliver regulated 5V for the
circuit.

When water in the tank rises to come in contact with the sensor, the base of transistor BC548 goes high. This high signal drives transistor BC548 into saturation and its collector goes low. The low signal is sensed by port pins of microcontroller IC2 to detect empty tank, dry sump and full tank, respectively.

Operation:
When water in the tank is below sensor A, the motor will switch on to fill water in the tank. The LCD module will show ‘motor on.’ The controller is programmed for a 10 minute time interval to check the dry-run condition of the motor. If water reaches sensor B within 10 minutes, the microcontroller comes out of the dry-run condition and allows the motor to keep pushing water in the tank.

The motor will remain ‘on’ until water reaches sensor C. Then it will stop automatically and the microcontroller will go into the standby mode. The LCD module will show ‘tank full’ followed by ‘standby mode’ after a few seconds. The ‘standby mode’ message is displayed
until water in the tank goes below sensor A.

In case water does not reach sensor B within 10 minutes, the microcontroller will go into the dryrunning mode and stop the motor for 5 minutes, allowing it to cool down. The LCD module will show ‘drysump1.’

After five minutes, the microcontroller will again switch on the motor for 10 minutes and check the status at sensor B. If water is still below sensor B, it will go into the dryrunning
mode and the LCD module will show ‘dry-sump2.’

The same procedure will repeat, and if the dry-run condition still persists, the display will show ‘drysump3’ and the microcontroller will not start the motor automatically. Now you have to check the line for water and manually reset the microcontroller to start operation.

In the whole procedure, the microcontroller checks for high and low voltages. For example, when the voltage is high, it will scan for about two seconds to check whether it is a fluctuation. If the voltage remains high after two seconds, the microcontroller will halt running of the motor. Now it will wait for the voltage to settle down. After the voltage becomes normal, it will still check for 90 seconds whether the voltage is normal or not. After normal condition, it will go in the standby mode and start the aforementioned procedure.

Practical applications:
This controller is useful for single-phase operated motor-pumps and the pumps that suck water from the ground water tank. A small push-to-off manual switch in series with sensor A can also make it useful for pumps that suck water from Jal Board’s supply. Because of the particular timing of this water supply, the controller must be switched on within the timing of the water supply and switched off when water is not being supplied.

When the controller is ‘on’ during the supply timings, it will wait for the tank to get empty before starting the motor. However, you can also start the motor using the pushbutton. The motor will turn on ignoring the status of the water level and will go through the aforementioned procedure.

Sensor positions in the tank:
Four non-corrosive metallic sensors are installed in the tank as shown in Fig.1. Sensor COM is connected to Vcc supply from the circuit. Sensor A detects the empty tank to start the motor. Sensor B detects dry-running condition of the motor and sensor C detects the full tank to stop the motor. Make sure that sensor B is around 2 cm above sensor A to check the dry-running condition properly.

Calibration:
Care must be taken when calibrating for under- and over-voltages. Always calibrate when the relay is in ‘on’ position. If you calibrate in the standby mode, it will trip at a voltage nearly 10 volts lower than the set voltage due to the loading effect.

Software:
The source code is written in Assembly language and assembled using 8051 cross-assembler. The generated Intel hex code is burnt into microcontroller AT89C51 using a suitable
programmer. The software is well commented and easy to understand. All the messages are displayed on the LCD module.

Download : Source Code

Component Required:

IC1, LM324

IC2, AT89C51

IC3, PC817

IC4, 7805

R1,R2,R7,R11,R12, 1K ohm

R3,R9, 560K ohm

R4,R5,R8, 2.7K ohm

R6, 330 ohm

R10, 470 ohm

R13, 100 ohm

R14, 10K ohm

R15-R17, 100K ohm

R18-R20, 2.2K ohm

R21,R22, 33 ohm

RNW1, 10K resistor network

C1-C3, 1000uF/35v electrolyte cap

C4, 220uF/25v electrolyte cap

C5,C6, 33pF ceramic cap

C7, 100uF/35v electrolyte cap

C8, 10uF/16v electrolyte cap

T1-T4, BC548

T5, SL100

D1-D14, 1N4007 Diode

VR1-VR2, 470 ohm pot

VR3, 10K pot

RL1, 12v Relay

X1, 230v to 12v, 500mA transformer

Xtal, 12MHz

S1, Push to on switch

S2,S3, on/off switch

16x1 LCD

Smart Voltage Stabilizer Using PIC16F877A

noreply@blogger.com (Albin George) — Tue, 29 Nov 2011 03:03:00 +0000

Voltage stabilizers are used for many appliances in homes, offices and industries. The mains supply suffers from large voltage drops due to losses on the distribution lines en route. A voltage stabilizer maintains the voltage to the appliance at the nominal value of around 220 volts even if the input mains fluctuates over a wide range.

Here is the circuit of an automatic voltage stabilizer that can be adapted to any power rating. Its intelligence lies in the program on PIC16F877A—a low-cost microcontroller that is readily available. The circuit, when used with any appliance, will maintain the voltage at around 220V even if the input mains voltage varies between 180V and 250V.

Here the circuit is shown for a 5A stabilizer. It acts within 100ms to produce a smoothly varying output whenever input mains voltage changes. (Servo stabilizers move a variable contact on a toroidal auto transformer to adjust the output when input goes up and down, which takes seconds.)

The PIC16F877A is an RISC (reduced instruction set computer) microcontroller with 35 instructions, and hence program development with it is rather tough. But, there are good support programs.

Circuit description:

The circuit is divided into two sections as it is easy to test them separately: voltage stabilizer controller and voltage stabilizer buck-boost. The sections can be joined easily.

Voltage stabilizer controller section:

This part of the circuit is built around the PIC microcontroller (see Fig. 1). The 5V supply for the microcontroller is derived from a small iron-core mains step-down transformer having 9-0-9V, 300mA rating, two diodes (1N4007) and a 1000μF capacitor followed by the 7805 regulator.

The ADC input channel 0 at port-A pin 2 of IC2 is used as shown in Fig. 1. Here potentiometer VR1 is connected to +5V and ground through a jumper connection. For the purpose of testing, you can vary VR1 to adjust the voltage from 0 to 5V. The reset circuitry at pin 1 (MCLR) has capacitor C1 and resistor R1. Pin 30 (port-D bit 7) gets a signal (marked as ‘D’) derived from the mains supply. Pins 17 and 16 (CCP1 and CCP2) provide the actual pulse output signal that helps in stabilizing the mains power. The signal is a set of equally spaced pulses at about 8 kHz for a 12MHz crystal.

The pulses from pins 16 and 17 are buffered using a pair of inverter gates of high current

driver IC ULN2003. Note that the gates in this chip need pull-up resistors Fig. 1: Circuit of voltage stabilizer controller section at the output pins. So at points marked ‘A’ and ‘B’ we get two pulse trains from the microcontroller. Synchronization with the mains supply is achieved by the square wave (50Hz mains derived) on port-D bit 7 (pin 30).

Transistor T3 (BC547) produces a rectangular pulse from the half-wave rectified low voltage (9V) from the transformer (9V-0-9V, 300mA). Using 50 Hz as reference for positive and negative half cycles of the mains supply, it produces the pulses at A and B points in turn. These pulses change in width and are hence called pulse width modulated. The width varies in accordance with the voltage to be produced for compensating the voltage from mains supply.

After wiring the circuit, program the chip with the given Assembly program. Insert the chip into the board and apply power supply. The chip has two PWM pins, 16 and 17. Adjust the shaft of pot-meter VR1 (10-kilo-ohm) to the bottom position for zero voltage. Also, ground pin D. The PWM pulse is now available from pin 17 of IC2, while pin 16 is low. If the shaft of the potmeter is moved to the top position when ‘D’ is connected to ground, pulses will be available from pin 16. Taking pin D to 5V reverses the above sequence. After checking this part of the circuit, the circuit shown in Fig. 2 may be tested.

In manual position of input selection switch S1 (Fig. 1), the analogue input voltage from pot-meter VR1 is used. In this position, the circuit functions as a variac that varies the output voltage from 180V to 250V as the pot-meter is varied.

In auto position of S1, the circuit acts as a stabilizer. For this, transformer rectified supply derived from the mains provides a proportional voltage to the ADC of the chip.

Point E in the voltage stabilizer controller circuit gives a voltage that varies with mains voltage. At exactly 220V mains, the 9V transformer (X1) gives a peak voltage of 9√2 =12.7V and subtracting 10V using zener diode ZD1 gives 2.7V at point E. It increases to 5V when the mains voltage rises to 259V and drops to zero when mains drops to 172V in effect, giving 0 to 5V over this range.

Using this voltage at point E, you can assess variation in the mains voltage and thereby control the PWM based sine voltage for adding (boost) or subtracting (buck) from mains. Point E is connected to the ADC input pin (point C) of the PIC in auto position (Fig. 1).

The buck-boost principle:

Voltage stabilizers buck (subtract) the mains voltage if it is higher than 220V and boost (add to) the mains voltage if it is lower than 220V. For this purpose, you need to produce a small voltage to do addition or subtraction. In Fig. 3, the mains voltage waveform is shown in the top left corner, with two voltages of smaller amplitude (about 30V) shown below it. One of these two voltages is in the same phase as the mains voltage, while the other is out of phase. By adding any of the two voltages, you can boost or buck the mains voltage.

For this purpose, ordinary voltage stabilizers generate a small voltage using a transformer with one or more taps. They connect the small voltage in series with the mains supply so as to add or subtract from it. A changeover relay is used to switch to buck/boost, while another relay selects between voltages from the two taps.

This method does not produce a smooth voltage change due to relay switching and the voltage from tap produces a fixed value (instead of a finely-variable voltage). In this project, the additional voltage of about 30V in phase or out of phase with the mains voltage is finely variable because of PWM. So it produces a smoothly varying output.

A typical PWM concept is shown in Fig. 4. The microcontroller produces pulse-widths, as required, for generating the voltage to be added or subtracted from the mains. The pulses from points A and B (refer Fig. 1) are fed to the transformer shown in Fig. 2. The secondary winding of this transformer gives the adding voltage. In this case, there is no relay switching; the buck or boost is done smoothly by changing the phase of the adding signal instantly. So it is a continuous voltage stabilizer. Depending on how much the input varies from 220V, pulse width is generated so as to adjust the output voltage by adding or subtracting from it. This is a feed-forward control.

Points marked ‘com’ common points in Figs 1 and 2 are not the ground and should not be connected to the neutral line.

Take care while checking the buck/boost circuit, as all the points are ‘hot’ and will give electric shock if touched, and also when interconnecting the voltage stabilizer control and buck-boost circuits.

Pulse-drive circuit and the transformer:

Fig. 2 shows the circuit to buck/boost the mains voltage using a buck-and-boost transformer. The iron core transformer used here is the same as used in voltage stabilizers. There is no tap on the secondary winding and the primary winding is center-tapped.

As with most transformers, the stampings used for this transformer are made of 4mm thick silicon steel. These are E-I type Stalloy/CRGO stampings. The size of the stampings depends on the rating. A toroidal winding transformer gives better performance and is smaller in size.

Here, we have used a 250V-0-250V, 500mA primary to 50V, 5A secondary transformer. The windings’ number of turns depends on the core size used.

Pulses from A and B of the voltage stabilizer controller circuit are fed to the gate pins of MOSFET power transistors (IRF840) via 10k series resistors. There are also 100-kilo-ohm grounding resistors connected to the transistors’ gates. The drains (D) are connected to the winding ends of transformer X2. The center tap of the primary winding is connected to the rectified DC supply from the mains. (This rectified voltage is not filtered; it is just unfiltered, rectified sine wave at point P.)

The power transistors (IRF840) switch the rectified sine voltage supply at the PWM frequency produced by the microcontroller. To smooth out the pulse switching, a 2.5μF, 400V AC fan capacitor is connected across the primary winding of transformer X2. The voltage induced in the secondary winding is a sine wave whose amplitude depends on the width of pulses at points A and B. The program changes the PWM width, and thus the amplitude of the sine wave, to adjust the mains voltage to 220V level.

We thus get a sine wave of the mains frequency. By serially adding the secondary voltage to the input mains voltage we get the stabilized voltage at the output of the unit.

On alternate half cycles, pulses at points A and B arrive to make either of the two transistors T1 and T2 conduct and allow the current to flow through the primary winding. A 2.5μF, 400V AC capacitor is required across the primary winding of transformer X2. Otherwise, only the pulses from A will pass through and buck and boost cannot be obtained.

In manual position of the switch, when potmeter VR1 is varied from bottom to top (0 to 5V), the voltage across the secondary decreases, crosses zero and then increases again. This means the secondary voltage varies with the potmeter position. Check the variation in secondary voltage by using a voltmeter, or a multimeter set to 50V AC range. The voltage should increase on either side of the mid-point of VR1. In auto position, combining the secondary output voltage of transformer X2 with the mains voltage gives you the stabilized output.

Testing:

First, test the controller circuit (Fig. 1) for pulse width modulated signals at points A and B. Check changeover from A to B by applying 0V and 5V at point D.

Check the circuit for a square wave of 5V amplitude at point D during positive half cycles of AC mains. This square wave is generated by the transistor fed with the unfiltered low voltage DC from transformer X1.

Vary the pot-meter in manual position of the switch. Using a CRO, you can see variation in the pulse-width (see Fig. 4).

As VR1 is adjusted beyond the mid position, pulses at points A and B toggle.

Note that the transistors are ‘hot’ and ‘live.’ Energize the voltage stabilizer controller circuit first but only in manual position of switch S1. Join points C and E and then switch on mains power for the buck and boost circuit.

Measure the AC voltage across the secondary output of transformer X2. Vary VR1 in the

controller section and check whether the voltage output at the secondary of X2 varies.

A CRO can be used to observe this secondary voltage. It should be 50Hz sine wave, but if

it has a break, it means the half cycles are not synchronized.

In Fig. 1, at point E, we have included a lag circuit comprising variable resistor VR2 (5 Kilo-ohm) and capacitor C5 (10μF). Adjust preset VR2 until the waveform is a smooth sine wave.

There may be small ripples in the first half of each cycle, but these do not matter and will

anyway be present due to PWM switching. Capacitor C7 (2.5μF) across the primary winding of transformer X2 filters them out.

The secondary voltage of transformer X2 should decrease and then increase as VR1 is raised from 0V position. Then check voltage regulation after changing over to auto position in Fig. 1. Adjust VR1 to the center position precisely. In the center position, there will be no pulse and therefore no adding voltage in the secondary winding. So the value of the zener diode used in the rectifier circuit should be changed in order to get 0V for 220V input. A variac is useful for varying the input voltage and checking the output.

Activate the buck-and-boost circuit by closing stabilizer switch S2 (Fig. 2).

Using a variac, the voltage can be varied and the stabilizer output observed on a voltmeter. If the voltage boosts up instead of bucking, reverse the secondary winding terminals connected in series to the mains.

Capacitor C6 (0.1μF) at the output terminals of X2 removes minor ripples, if any, in the waveform.

The optional input voltage display circuit consists of three common-anode, seven-segment LEDs (each LTS542) shown in Fig. 5. The seven-segment LED displays are driven from port-B of the chip in a multiplexed manner. The anode selections are made through bits 0 through 2 from port-D via transistors T4 through T6, respectively.

Download : Source Code

Component Required:

IC1, 7805 voltage regulator

IC2, PIC16F877A microcontroller

IC3, ULN2003 buffer

D1-D8, 1N4007 diode

T1,T2, IRF840 MOSFET

T3, BC547 npn bipolar transistor

ZD1, 10V zener diode

R1, R3-R8, R10, R12, R13, 10 K ohm

R2, 4.7-kilo-ohm

R9, R11, 100-kilo-ohm

VR1 10-kilo-ohm potmeter

VR2, 5-kilo-ohm preset

C1, 100nF ceramic

C2, 1000μF, 25V electrolytic

C3, C4, 22pF ceramic

C5, 10μF, 25V electrolytic

C6, 0.1μF, 400V AC

C7, 2.5μF, 400V AC

X1, - 230V AC primary to 9V-0-9V, 300mA secondary transformer

X2, - 250V-0-250V, 500mA primary to 50V, 5A secondary transformer

Xtal, - 4MHz crystal oscillator

S1, - SPDT changeover switch

S2, - On/off power switch (5A)

Motion Sensor for security Light

noreply@blogger.com (Albin George) — Sun, 27 Nov 2011 17:43:00 +0000

Here is a system based on PIR motion detector module BS1600 (or BS1700) that can be used for security or corridor lighting in power saving mode.The 12V DC power supply required for the motion detector and the relay driver is derived from 230V, 50Hz mains using a transformerless circuit as shown in Fig. 1. The working of the circuit is simple. When you power-on the circuit after assembling all the components including the CFL, the CFL will glow for 10 seconds, turn off for 30 seconds, glow for 10 seconds and then turn off.

Now the circuit is ready to work.When any movement is detected, around 3.3V appears on the base of relay-driver transistor T1 and it conducts to energise relay RL1. As a result, Triac1 (BT136) fires to provide full 230V and light up the CFL. Another normally-opened contact of the relay (N/O2) is used here to hold the output until reset. If the switch is not in ‘hold’ position, the light will remain ‘on’ for about ten seconds (as programmed in the motion sensor). In short, when there is a movement near the sensor, the CFL glows for about ten seconds. It will remain ‘on’ if switch S1 is in ‘hold’ position. Assemble the circuit on a general-purpose PCB and enclose in a suitable cabinet. Use a three-pin connector for connecting the PIR sensor in the circuit with correct polarity. The motion detector is embedded onto the transparent cover of the light assembly as shown in Fig. 2

Clock Timer

noreply@blogger.com (Albin George) — Sat, 01 Oct 2011 01:40:00 +0000

With this simple clock controlled timer, you will never again miss your favourite TV or radio programme. The TV or radio will switch on automatically at the time preset by you and will remain ‘on’ until the power supply fails or is disconnected.

The circuit uses the AC signals generated at the buzzer terminals of an alarm clock. The AC signals are amplified by transistors T1 and T2 and the amplified output from the emitter of T2 is fed to the inverting input of negative-voltage comparator IC LM311 (IC1). The non-inverting input of IC1 gets a presettable voltage through preset VR1. The inverting and non-inverting inputs of LM311 are different from other op-amps and it outputs sink current through pin 7 or source current through pin 1.

When pin 3 of IC1 is at a higher voltage than pin 2, its output sinks as indicated by LED1. This gives a short negative pulse to the monostable wired around timer NE555. Resistor R5 keeps trigger pin 2 of IC2 high. The short-interval monostable outputs a high signal for a brief period to the gate of SCR1 (BT169) and relay RL1 energises. The latching action of SCR1 keeps the relay pulled even when the output of the monostable turns low. The relay can be de-energised by disconnecting the supply to the circuit via switch S1.

The circuit works off a 9V battery. Assemble it on a general-purpose PCB and enclose in a suitable cabinet. Provide an AC outlet in the cabinet to switch on the appliance using the circuit. As mentioned earlier, the input signal is obtained from the buzzer terminals of the clock. Remove the small buzzer of the clock and connect point ‘A’ to the positive terminal and point ‘B’ to the negative terminal of the buzzer. Connect the mains AC terminal outlet to the normally- opened (N/O) contact of relay RL1. So when the relay energises, 230V AC operates the connected appliance. Set the desired time in the clock by adjusting the alarm set-up and switch on the circuit. When the set time reaches, the appliance will switch on automatically. The circuit can also be connected to digital clocks.

Stereo Amplifier

noreply@blogger.com (Albin George) — Sun, 25 Sep 2011 12:22:00 +0000

The TDA2030A is a monolithic IC intended for use as low frequency class AB amplifier. The TDA 2030A is an 18watt 22Volt type update of the earlier 2030 whose power is limited to 14 watt RMS.

It provides high output current and has very low harmonic and cross-over distortion. Further the device incorporates a short circuit protection system comprising an arrangement for automatically limiting the dissipated power so as to keep the working point of the output transistors within their safe operating area. A conventional thermal shut-down system is also included.

The circuit has two AF amplifiers. In the circuit diagram, shown in Fig. 2, C5 and C12 are the input capacitors and R1 and R5 limit the impedance. R2, R3, R6, R7, C6 and C13 set the gain and

response. The D5, D6, D7 and D8 may be added for the safety of the circuit. As shown in Figure 5 the mains supply is stepped down to 15-0-15V AC by step-down transformer X1. The output

of the transformer is rectified and filtered by diodes D1 through D4 and capacitors C1 through C4.

SEMICONDUCTORS

IC1,IC2 - TDA 2030A
D1-D4 -1N4007
D5-D8 - 1N4001

RESISTORS

R1, R5 - 100kW
R2, R6 - 2.2kW
R3, R7 - 82kW
R4, R8 - 2.2W
VR1 - 220K

CAPACITORS

C1,C2 - 2200μF/35V
C3,C4 - 0.01μF
C5, C12 - 0.47μF
C6, C13 - 10μF/25V
C7, C14,C10,C17 - 100μF/35V
C8, C15,C11,C18 - 0.1μF
C9, C16 - 0.22μF

MISCELLANEOUS

X1 - 230V AC Primary to 15-0-15V, 1A Secondary Transformer
LS1,LS2 - 4 Ohms, 20Watt

Current Sensor

noreply@blogger.com (Albin George) — Sun, 25 Sep 2011 11:54:00 +0000

High-wattage appliances like electric irons, ovens and heaters result in unnecessary power loss if left ‘on’ for hours unnoticed. Here is a circuit that senses the flow of current through the appliances and gives audible beeps every fifteen minutes to remind you of power-’on’ status.

This is a non-contact version of current monitor and can sense the flow of current in high-current appliances from a distance of up to 30 cm . It uses a standard step-down transformer (0-9V, 500mA) as the current sensor. Its secondary winding is left open, while the primary winding ends are used to detect the current. The primary ends of the transformer are connected to a full-wave bridge rectifier comprising diodes D1 through D4. The rectified output is connected to the non-inverting input of IC CA3140 (IC1).

IC CA3140 is a 4.5MHz BIMOS operational amplifier with MOSFET input and bipolar transistor output. It has gate-protected MOSFET (PMOS) transistors in the input to provide very high input impedance (1.5 T-ohms),very low input current (10 pA) and high-speed switching performance.

The inverting input of IC1 is preset with VR1. In the standby mode, the primary of the transformer accepts e.m.f. from the instrument or surrounding atmosphere, which results in low-voltage input to IC1. This low voltage at the non-inverting input keeps the output of IC1 low. Thus transistor T1 doesn’t conduct and pin 12 of IC2 goes high to disable IC2. As a result, the remaining part of the circuit gets inactivated.

When a high-current appliance is switched on, there will be a current drain in the primary of the transformer to the negative rail due to an increase in the e.m.f. caused by the flow of current through the appliance. This results in voltage rise at the non-inverting input and the output of IC1 becomes high. This high output drives transistor T1 into conduction and the reset pin of IC2 becomes low, which enables IC2.

IC CD4060 (IC2) is a 14-stage ripple counter. It is used as a 15-minute timer by feeding Q9 output to the piezobuzzer for aural alarm through the intermediate circuitry. Resistors R5 and R6 along with capacitor C1 maintain the oscillations in IC2 as indicated by blinking LED1. The high output from IC2 is used to activate a simple oscillator comprising transistors T2 and T3, resistors R8 and R10, and capacitor C2.

When the Q9 output of IC2 becomes high, zener diode ZD1 provides 3.1 volts to the base of transitor T2. Since transistor T2 is biased by a highvalue resistor (R8), it will not conduct immediately. Capacitor C2 slowly charges and when the voltage at the base of T2 increases above 0.6 volt, it conducts. When T2 conducts, the base of T3 turns low and it also conducts. The piezobuzzer connected to the collector of T3 gives a short beep as capacitor C2 discharges. This sequence of IC2 output at Q9 becoming high and conduction of transistors T2 and T3 resulting in beep sound repeats at short intervals.

Remote Switch

noreply@blogger.com (Albin George) — Sat, 24 Sep 2011 14:10:00 +0000

This circuit can be used to activate the master switch from the bed without searching for the switch in darkness. It can be activated by the TV remote handset. The security lamps glow for three minutes and then turn off. The circuit is sensitive and can be activated from a distance of up to 25 metres.

IR receiver module TSOP 1738 (IRX1) is used to sense the pulsed 38kHz IR rays from the TV remote handset. The IR receiver module has a PIN photodiode and a preamplifier enclosed in an IR filter epoxy case. Its open-collector output is 5 volts at 5mA current in the standby mode.

In the standby mode, no IR rays from the remote handset fall on the IR receiver, so its output pin 3 remains high and LED1 doesn’t glow. Through resistor R2, the base of transistor T1 remains high and it does not conduct. As a result, the voltage at pin 3 of IC CA3130 (IC1) remains low. The potential divider comprising resistors R4 and R5 maintains half of 5.1V at pin 2 of IC1. In brief, the voltage at pin 2 of IC1 is higher than at pin 3 and its output remains low. LED2 remains ‘off’ and transistor T2 does not conduct. Relay RL1 remains de-energised and, as a result,security lamps (both indoors and outdoors) remain switched off.

When you press any key of the remote TV handset, IR rays fall on the receiver (IRX1) and its output goes low. LED1 flashes in sync with pulsation of the IR rays. At the same time, transistor T1 (BC558) conducts to take pin 3 of IC1 high. IC1 is used as a comparator with timer action.

When transistor T1 conducts, pin 3 of IC1 gets a higher voltage than pin 2 making the output of IC1 high. Meanwhile, capacitor C4 charges to full voltage and keeps pin 3 high for a few minutes even after T1 is non-conducting. Resistor R3 provides discharge path for capacitor C4, which decides the time period for which the output of comparator IC1 should remain high.

The high output of IC1 energises relay RL1 through relay-driver transistor T2. Thus the load, i.e., security lamps, turn on for three to four minutes. LED2 glows to indicate activation of the relay as well as switching ‘on’ of the security lights. Connect a single-pole, single-throw ‘on’/‘off’ switch (MS) to activate the security lamps manually when required.

Zener diode ZD1 provides 5.1V DC for safe operation of the IR receiver and associated circuit. Power for the circuit is derived from a step-down transformer (X1) and a bridge rectifier comprising diodes D1 through D4.Smoothing capacitor C1 removes ripples, if any, from the power supply.

Assemble the circuit on a general purpose PCB and enclose in a suitable cabinet. Drill holes on the front panel for mounting the IR sensor and LEDs. Connect the master switch between the normally-open (N/O) contact and pole of relay RL1 so that the master switch can be used when needed. The relay contacts rating should be more than 4A. Mount the unit near the master switch using minimal wiring.

Emergency Light

noreply@blogger.com (Albin George) — Sat, 24 Sep 2011 11:11:00 +0000

This emergency light has the following two advantages:

1. It turns on automatically when the mains power fails, so you

need not search it in the dark.

2. Its battery starts charging as soon as the mains resumes.Operation of the circuit is quite straightforward. Mains supply is stepped down by transformer X1, rectified

by a full-wave rectifier comprising diodes D1 and D2, filtered by capacitor

C1 and fed to relay coil RL1. The relay energises to connect the battery

to the charging circuit through its normally-opened (N/O) contacts. Freewheeling

diode D3 acts as a spike buster for the relay.

The charging circuit is built around npn transistor BD139 (T1). The transformer

output is fed to the collector of transistor T1, which provides a fixed

bias voltage of 6.8V to charge the battery. When the battery is fully charged,

the battery voltage becomes equal to the breakdown voltage

of the zener diode(ZD1). Zener diode ZD1 conducts to provide an alternative path for the current to ground and battery charging stops. When mains fails,relay RL1 de-energises. The battery now gets connected to the white LED array (comprising LED1 through LED6) through current-limiting resistor R2. The LEDs glow to light up the room. To increase the brightness in your room,you can increase the number of white

LEDs after reducing the value of resistor R2 and also use a reflector assembly.

Clap Switch

noreply@blogger.com (Albin George) — Sat, 24 Sep 2011 11:05:00 +0000

Here is a clap switch which is used to
turn ON/OFF any appliance
connected to it. The circuit changes
its output state when you clap near
the condensor mic.

Working:
The Clap sound sensed by condenser microphone is amplified by transistor
T1. The amplified signal provides a pulse to pin 2 of IC1, triggering IC1.
IC1, commonly used as a timer, is wired here as a monostable multivibrator.
Triggering of IC1 causes pin 3 to go high it remains high for a
certain time period depending on the selected values of R7 & C3. This ‘ON’
time (T) of IC1 can be calculated using the following relationship
T=1.1R7 C3 seconds. Where R7 is in Ohms & c3 in microfarads. On giving
a clap, output pin 3of IC1 goes high & remains in this standby position for
the preset time. This provides a pulse at clock pin 14 of decade counter IC
4017 (IC2). Decade counter IC2 is wired here as a bistable.
Each pulse applied at clock pin 14 changes the output state at pin2 of
IC2 because Q2 is connected to reset pin 15. The high output at pin 2 drives
transistor T2 & also energises relay RL1. LED1 indicates activation of
relay RL1 & ON/OFF status of the appliance. A free-wheeling diode (D1)
prevents damage of T2 when relayde-energises.

Light Switch

noreply@blogger.com (Albin George) — Wed, 21 Sep 2011 14:31:00 +0000

The circuit which is being presented here is a switch that will be activated by light falling on a sensor.The circuit uses a Light Dependent Resistor (LDR) as a sensor and three transistors to amplify the signals from the LDR and drive the relay which does the switching.

The circuit diagram is shown in figure

1. As you can see from the circuit diagram in the input of the circuit there is a
potentiometer (VR1) connected in series with the LDR in such a way as to
form a voltage divider. When light falls on the LDR it causes its resistance to
change and this causes the voltage across the LDR to change accordingly.
These voltage changes are used to change the state of the transistor Q1
switching it ON and OFF. The output from Q1 drives Q2 and this in turn Q3
which drives the output relay. The diode D1 protects the transistor from
the back emf that is produced from the relay coil when it is turned off. The VR1 adjusts the sensitivity of the circuit so it is possible to use it under widely different conditions. The circuit operates from a 12 VDC power supply.

Water Level Indicator With Alarm

noreply@blogger.com (Albin George) — Wed, 21 Sep 2011 11:17:00 +0000

Here is a simple, versatile cir- cuit which indicates the level of water in a tank. This circuit produces alarm when water level is below the lowest level L1 and also when water just touches the highest level L12. The circuit is designed to display 12 different levels. However, these display levels can be increased or decreased depending upon the level resolution required. This can be done by increasing or decreasing the number of level detector metal strips (L1 to L12) and their associated components. In the circuit, diodes D1, D2 and D13 form half-wave rectifiers. The rectified output is filtered using capacitors C1 through C3 respectively. Initially, when water level is below strip L1, the mains supply frequency oscillations are not transferred to diode D1. Thus its output is low and LED1 does not glow. Also, since base voltage of transister T1 is low, it is in cut-off state and its collector voltage is high, which enables tone generating IC1 (UM66) and alarm is sounded. When water just touches level detector strip L1, the supply frequency oscillations are transferred to diode D1. It rectifies the supply voltage and a positive DC voltage develops across capacitor C1, which lights up LED1. At the same time base voltage for transistor T1 becomes high, which makes it forward biased and its collector voltage falls to near-ground potential. This disables IC1 (UM66) and alarm cannot be sounded. Depending upon quantity of water present in the tank, corresponding level indicating LEDs glow. It thus displays intermediate water levels in the tank in bar-graph style. When water in the tank just touches the highest level detector strip L12, the DC voltage is developed across capacitor C2. This enables tone generating IC1 (UM66) and alarm is again sounded. .

UFO round LED Chaser

noreply@blogger.com (Albin George) — Wed, 21 Sep 2011 11:13:00 +0000

The heart of the LED chaser is the PIC 16F628A microcontroller, IC2. The program that runs on this chip controls the LEDs attached to the output port pins. Resistors R1 thru R8 limit the current through LED1 - LED8 to a safe level that won't damage the PICs I/O ports or LEDs. Resistor R9 provides a pull-up for the input connected to switch S1. R10 holds the PICs MCLR reset signal high.

Capacitor C1 is used to decouple the 5 volt power supply to the PIC. If you're building the circuit on a breadboard or stripboard you should ensure it is located close to the PICs Vdd connection (pin 14 ).

Power is supplied to the circuit via the V+/V- solder points. The voltage regulator used is a LM2931-5.0, low-drop-out regulator and will maintain regulation with an input voltage down to 6 volts. Input voltage for the LED chaser should be between 6 volts and 14 volts to ensure power dissipation remains within limits. The LM2931-5.0 regulator is designed for battery powered and automotive applications and includes internal current limiting, thermal shutdown, as well as reverse battery connection without damage to itself or the circuit behind it. Capacitor C3 is important and must be fitted to prevent instability of the regulator output

Typical current drawn by the circuit with all LEDs on is only around 80mA; with all LEDs off it's under 1mA.

Notes:

* The latest high brightness LEDs are very bright even with 330R current limiting resistors. However, if you do need to change these resistors for some reason take into account the absolute maximum current that the on-board voltage regulator can deliver is 100mA.

* If you do change the current limit resistors to suit different LEDs you should aim for the LED current for each output to be no more than 10mA ( 80mA total for all 8 outputs)

* The 330R resistors are specified so that with a LED forward voltage of 1.7 volts and the circuit operating at 5 volts the LED current will be 10mA. LEDs with a higher forward voltage will draw less current. Most LEDs have a forward voltage greater than 1.7 volts so the circuit will work with the majority of LEDs and stay well within the design limits of the circuit.

* The LED forward voltage parameter for a specific LED will normally be found in the manufacturers data sheet.

STRIP LED LAMP

noreply@blogger.com (Albin George) — Wed, 21 Sep 2011 10:56:00 +0000

Strip LEDs are available in differ¬ent colours powered by direct current (DC) source. These LEDs are available as surface mount devices with current limiting resistors. Usually there are 300 LEDs in a 5-metre strip. The strip can be cut into pieces so that the bits having three or four LEDs can be used with 12V DC source. The cir¬cuit given here uses the strip LEDs to make an automatic white LED lighting source.
The circuit is powered by a ca¬pacitor power supply connected to AC mains. Capacitor C1 drops the 230V AC, which is further rectified by the bridge rectifier module and is made ripple-free by C2. Zener diode (ZD1) provides 12V DC to the comparator circuit. Resistor R1 is important in the power supply as it provides discharge path to the voltage stored in capacitor C1 after the circuit is unplugged from main.
The automatic working of the circuit is based on the light-sensing prop¬erty of the light-dependent resistor (LDR). Operational amplifier CA3140 (IC1) is used as a comparator with two potential dividers in its inverting and non-inverting inputs. LDR1 and resistor R3 form one potential divider that provides a variable voltage at the inverting input pin 2 of IC1. Second potential divider comprises resistors R4 and R5, which provide half of the supply voltage (6V) to the non-invert¬ing pin 3 of IC1. The output of IC1 depends on voltage level at inverting input pin 2 of IC1 as explained below.

In daylight, LDR1 has low resist¬ance and the voltage at inverting input (pin 2) of IC1 is more than that of non-inverting input (pin 3). This makes IC1 output low, which drives transistor T1 into cut-off condition and strip LEDs do not glow.
However, at night the light incident on LDR1 is low and its resistance is high. The voltage at inverting input of the comparator decreases, making it lower than the voltage at non-inverting input. This makes IC1 output high. Transistor T1 goes into saturation, thus connecting cathodes of LEDs to ground. All the LEDs in the strip turn on and remain that way till morning.
Assemble the circuit on a general-purpose PCB and enclose it in a suit¬able shock-proof case. Strip LEDs are available in ribbon-shaped form. Use 5cm bits (two bits) having three LEDs each. The strip can be cut at supply-contact points. Strip LEDs are arranged on a flexible belt with double-sided adhesive on the back side, so it can be glued to any surface. Connect the LED strip in the circuit with correct polarity.