BATTERY DEEP DISCHARGE  SAVER 

hello  friends  today I am gonna  telling  you  about  some  easy  and valuable  electronics projects for  school and  college  practical 

This circuit can be used to ensure that a 12V sealed lead acid battery does not go into the condition of deep discharge.  The circuit disconnects the battery from load when its voltage goes below a preset voltage say (10.5v) level.  The load remains disconnected until the battery is recharged 

Initially, when the circuit is switched through switch S1. capacitor C1 momentarily acts as short circuit It connects the coil of relay RL1 to the battery. Relay RL1 energies and  connects the load to the battery.  At the same time battery terminal voltage is divided by resistor R2 and the combination of preset VR1 and R3 that provide reference voltage . The battery voltage does not go below the reference voltage preventing it from going into deep discharge 

Fig1;circuit diagram

The heart of the circuit is IC TL431 ( IC1) , which is a well - known voltage reference IC . The battery voltage is compared with the internal reference voltage of regulator IC1 . As long as the voltage set by the preset VR1 is above the internal reference voltage , IC1 allows relay RL1 to energise connecting the load to the battery As the battery begins to discharge its terminal voltage decreases When the battery voltage reaches the set voltage , say 10.5V , the cathode of IC1 goes high , which de - energies relay RL1 and disconnects the load from the battery  

Assemble the circuit on a general purpose PCB and set the low cut - off voltage (deep discharge voltage) of the battery.  For setting the low cut off voltage, remove the battery from the circuit and connect the circuit to a variable 12V DC power supply.  Also connect a digital multimeter across the variable power supply.  Increase the voltage from 0 to 12V through the variable power supply and read the voltage in multimeter Ads preset VR1 in such a way that relay RL1 gets energed and load is connected to the battery. Now decrease the supply to 10.5V (low battery volt age setting recommended by manufacturers to avoid deep discharge).  Move the preset VR1 slowly until the relay de - energises.  You may try this adjustment more than once to get IC to switch at exactly 10.5V.  After the adjustment is done remove the variable power supply and multimeter and reconnect the battery and switch on SL 

NOTE  After calibration, endose the assembled unit in a suitable shock - proof cabinet fix on / off switch S1 on the front panel and a two -  pin connector for load on the back panel.  Keep the battery inside the cabinet •

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 VARIVALE TIMER WITH MUSIC PROJECT 

hello  friends  today I am gonna  telling  you  about  some  easy  and valuable  electronics projects for  school and  college  practical

This simple timer can be set to run for different time settings (30 seconds to 4.5 minutes). Also, a musical note is played at the end of the set timing.

Timer IC NE555 (IC1) is wired as an astable multivibrator (AVM). The AVM is set to 0.033HZ frequency using preset VR1. It means that the time period is around 30 seconds. The output of IC1 goes high for around 20 seconds and low for around 10 seconds. As it changes from low to high, decade counter IC CD4017 (IC2) is advanced by one count. IC2 has ten outputs Q0 through Q9.

Switch S2 resets the counter which takes Q0 to logic high. Counting starts when switch S2 is released. Output Q1 goes high on the next positive-going pulse from IC1. IC2 is then incremented on each clock. Outputs Q1 through Q9 of IC2 go high one-by-one at interval of 30 seconds. 

The rotary switch S3 selects one of these outputs and provides 3.1V power supply to melody generator IC UM66 (IC3). UM66 produces a musical signal on its output pin 1. The musical signal is amplified by transistor T1 and drives the speaker to produce the musical note.

Fig1; circuit diagram

When rotary switch S3 is connected to Q1 output of IC2 and reset switch S2 is pressed, a musical note is heard after a few seconds for 30 seconds. For positions 2 to 9, the silent period increases by 30 seconds at each step. At position 10 of rotary switch S3, the delay will be of four and a half minutes, followed by 30 seconds of music. 

The best way to think about this is that positions 1 to 9 add 30-second delay each. If you let the timer continue to run, it repeats the tune every 5 minutes, irrespective of the setting of S3. 

The circuit runs on 6V, provided by four AA cells in a battery holder. A PP3-type clip is used to connect this to the circuit. S1 is a simple single-pole, single-throw (SPST) switch.

Assemble the circuit on a general- purpose PCB and enclose it in a suitable box. If you have a multimeter with a frequency-measuring facility, it would be ideal for setting the frequency of IC1 at pin 3 at around 0.033HZ. 

Check that IC2 outputs run through the correct sequence (30 SECOND ). Wire the loud- speaker to its terminal pins using external wires. Fix rotary switch S3 in the front panel for selecting the time. The positions of rotary switch S3 can be labeled with stick-on tape labels. A simpler technique is to punch small discs from insulating tapes of various colours and stick these around the knob.

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            STRIP LED LAMP PROJECT

hello  friends  today I am gonna  telling  you  about  some  easy  and valuable  electronics projects for  school and  college  practical

Strip LEDs are available in different 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 circuit given here uses the strip LEDs to make an automatic white LED lighting source. 

The circuit is powered by a capacitor 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 mains. 

Fig1;circuit diagram

The automatic working of the circuit is based on the light-sensing property 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-inverting 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 resistance 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 suitable shock-proof case. Strip LEDs are available in ribbon-shaped form. Use 5cm 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.

 note Since the circuit uses 230V AC, there is a risk of electrical shock. Do not touch or troubleshoot when the circuit is plugged in. Before connecting the circuit to the power supply section, test it using 12V DC from a battery or DC power supply.

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      CAR REVERSE HOREN PROJECT

101％ working  project hello  friends  today I am gonna  telling  you  about  some  easy  and valuable  electronics projects for  school and  college  practical

This car reverse horn can be used with any vehicle having a 12V battery. Transistors T2 and T3 form an astable multivibrator (AMV) that generates beeping tone signals. Medium-power PNP transistor T1 functions as a simple speaker amplifier.BD139 (T4) is an NPN medium-power transistor.

 A 5.6V zener diode (ZD1) is connected to its base. ZD1 provides 5.6V DC regulated power supply to the horn circuit built around transistors T1 through T3. Diode D1 functions as reverse polarity protector. 12V DC to the circuit is connected via brake switch of the car/ three-wheeler. 

Fig1; circuit diagram

When you reverse your vehicle, the circuit is connected to the battery of the car through the brake switch. The AMV oscillates and produces an audio frequency, which is given to speaker driver transistor T1 to generate a beeping tone. This tone can be altered by changing the values of capacitors C2 through C4 in multivibrator circuit.

Assemble the circuit on a general-purpose PCB and enclose in a suitable box. Con- nect 12V DC power supply to the circuit through the brake switch. When you reverse your car the circuit gets 12V required for its working. Place the cabinet in the vehicle such that it produces sound at the rear while reversing the car..

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          DIAC CONTROLLED  FLASHER 

101％ working  project hello  friends  today I am gonna  telling  you  about  some  easy  and valuable  electronics projects for  school and  college  practical

This simple flasher finds various industrial applications as a high - voltage indicator or machine - ' on' indicator . It flashes once every second to give a warning indication . It is simple to design and can be wired lead - to - lead without using PCB. It is directly powered from 220V AC and can be enclosed in the mains box.

Mains 230V AC is rectified by Di. which reduces it to a safer level through 33 kilo-ohm resistor R1 . Capacitor C1 ( 470pF , 100V ) charges through diode D1 and resistor R1`which reduces the flow of current to the diac and hence the triac remains non - conducting.

After capacitor C1 is fully charged the voltage across the diac rises and it conducts . This provides gate current to the triac through R2 . The triac fires and completes the circuit of the lamp and it glows.

Fig1; circuit diagram

The triac ( BT136 ) comprises two silicon - controlled rectifiers ( SCRs ) connected in the reverse parallel configuration sharing the same gate circuit . When the triac fires , both the SCR portions conduct . The gate of the triac is quite complex and it can be triggered by DC , rectified AC , AC or pulse sources like neon lamps or switching diodes like diacs. 

When the diac conducts , capacitor C1 discharges through the diac and R2 This reduces the gate current of the triac and it switches off . The lamp again turns on when C1 charges again. Thus the charging discharging cycle of capacitor C1 determines the flash rate of the lamp.

Since the circuit uses 220V AC , all the points are at mains lethal potential . Adequate spacing and use of lead sleeving is required as saftey measures while assembling the circuit . Do not enclose the circuit in a metallic cabinet unless it is made fully shockproof Also , do not solder or desolder the components when the circuit is powered .

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             EARTHQUAKE SENSOR 

101％ working  project hello  friends  today I am gonna  telling  you  about  some  easy  and valuable  electronics projects for  school and  college  practical

His circuit emulates a Earthquake(seismic) sensor to detect vibrations / sounds.  It is very sensitive and can detect vibrations caused by movement of animals or humans.  Therefore it can be used to monitor protected areas to restrict the entry of unwanted individuals or animals.
The circuit uses readily available components and the design is straight forward.  A standard piezo sensor is used to detect vibrational sounds due to pressure changes. The piezo element acts as a small capacitor having a capacitance of a few (nF) nanofarads. Like a capacitor, it can store charge when a potential is applied to its terminals. It discharges through VR1, when it is disturbed.

 In the circuit, IC TLO71 (1CI) is wired as a differential amplifier with both its inverting and non-inverting inputs tied to the negative rail through a resistive network comprising R1, R2 and R3. Under idle conditions (as adjusted by VR1), both the inputs receive almost equal voltages, which keeps the output low. TLO71 is a low-noise JFET input op-amp with low input bias and off-set current. The BIFET technology provides fast slew rates. Capacitor C1 is provided in the circuit to keep the differential input of IC1 for better performance.

Fig1;circuit diagram

When the piezo element is disturbed (by even a slight movement), it discharges the stored charge. This alters the voltage level at the inputs of IC1 and the output momentarily swings high as indicated by green LED1. This high output is used to trigger switching transistor T1, which triggers monostable IC2. The timing period of IC2 is determined by R7 and C5, With the shown values, it will be around two minutes. The high output from IC2 activates T2 and the buzzer starts beeping along with red light indication from LED2. 

Assemble the circuit on a common PCB and enclose in a suitable cabinet. Connect the piezo element to the PCB using single-core shielded wire. Enclose the piezo element inside a rustproof, small aluminium box. The piezo element should be firmly glued to the enclosure facing the fine side towards the case. Fix the sensor assembly on the back side of a ceramic tile or granite tile with good adhesive. Fix the tile (or bury it in the earth) near the entrance with the sensor assembly facing downwards. Whenever a pressure change develops near the sensor, the circuit will be activated.

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      AUDIBLE IR PROXIMITY DETECTOR

101％ working  project hello  friends  today I am gonna  telling  you  about  some  easy  and valuable  electronics projects for  school and  college  practical

This circuit gives an audible indication when any object reflecting sensor (containing IR LED and phototransistor). The sound generated by the front of the sensor will be louder if the object close to the reflecting sensor is opaque.

The home-made reflecting sensor contains a 5mm IR LED and a phototransistor. It can detect up to a longer range than commercial sensors like HO-4R. It can be used for indoor IR proximity detection.

The circuit uses an IC 555 wired as astable multivibrator. The 10kHz signal produced by the multivibrator is fed to the base of transistor T1. This signal is further fed to the IR transmitting LED used in the sensor. When an object comes in front of the sensor, modulated light emitted by the transmitting LED of the sensor is reflected back and sensed by the phototransistor of the same sensor.

Fig1;Circuit Diagram

The signals sensed by the phototransistor of the sensor are amplified by transistor preamplifier T2. These are further fed to a power amplifier based on IC LM386 to drive a speaker. The tone of sound can be varied by changing the value of tone capacitor C3 of IC1 (NE555).

To make a home-made sensor place the IR transmitting LED and the phototransistor in a piece of bakelite, parallel to each other such that the transmitted IR beam, after reflection, can be received by the phototransistor. 

The circuit works off a 9V battery. Assemble it on a general-purpose PCB and enclose in a suitable cabinet. Connect the sensor such that it is oriented towards an approaching object.

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