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Dancing Light

Introduction :

Here is a simple dancing light circuit based on NE555 (IC1) & CD4017 (IC2) . The IC1 is wired as an Astable multivibrator to provide the clock pulses for the CD4017. For each clock pulse receiving at the clock input (pin14) of IC CD4017, the outputs Q0 to Q9 (refer pin diagram of CD 4017) becomes high one by one alternatively. The LEDs connected to these pins glow in the same fashion to give a dancing effect. The speed of the dancing LEDs depend on the frequency of the clock pulses generated by the IC1. Decade counter CD4017 use to build all kinds of timer, LED sequencers and controllers circuits.

Circuit diagram :

Components Used :

• NE555 Timer IC
• Decade Counter CD4017
• 9V Battery
• Resistors
• Leds
• Variable Resistors
• Capacitors

Notes :

• Assemble the circuit on a good quality PCB or common board.
• The ICs must be mounted on holders.
• The speed of the dancing LEDs can be adjusted by varying POT R2.
• The capacitor C1 must be rated 15V.
• Using different color LEDs could produce a better visual effect.

Modifications :

• Dancing Light of different color can be obtained by using different color Leds.
• For varying speed of dancing light variable resistor can be used of various ratings.
• More lights can be added by enhancing the circuit.

Dark detector circuit

Introduction:

The dark detector circuit can be used to produce an audible alarm when the light inside a room goes OFF. The circuit is build around timer IC NE555. A general purpose LDR is used for sensing the light. When proper light is falling on the LDR its resistance is very low. When there is no light the LDR resistance increases. At this time the IC is triggered and drives the buzzer to produce an alarm sound. If a transistor and relay is connected at the output (pin3) of IC1 instead of the buzzer, electrical appliances can be switched according to the light.

Circuit diagram: 

Component used:

• 555 Timer IC
• One 1 megaohm resistor
• One 100K resistor
• One 100 ohm resistor (a 100 ohm potentiometer is better but optional)
• One 1000 picofarad capacitor
• A 9V battery
• A Piezo siren/buzzer

Modifications:

• This dark detector circuit can produces a musical sound whenever you put your hand on the sensor or a shadow of the person falls on sensor.
• The LDR ,R4 can be any general purpose LDR.
• The circuit must be assembled on a good quality PCB or common board.
• The circuit can be powered from a 9V PP3 battery.
• The POT,R3 can be used as a volume controller.
• The piezo can also be a speaker.

Applications:

• It is a perfect technique in a restricted area where only authorized person is allowed.
• It can be used to alert that somebody is present on door even before the person presses the door bell.

Digital Thermometer Circuit

Intorduction:

A simple thermometer circuit display used to display the value of the temperature upto 100 °C. The brain of this circuit is PIC16C74A; a Microcontroller from Microchip and it is easily available. It has an inbuilt 8bit multichannel Analog to digital converter, and also has many additional features.

Theory:

The temperature-sensing element is LM35, This chip has DC voltage output (10mV/°C) interface, which is fairly linear and easy to interface with the PIC16C74A. It does not require any external calibration or trimming and provides typical accuracy of +/-0.25°C at room temperature. It can measure +2°C to +150°C, and if the circuit changed a little, then it can be used to measure temperature from –55°C to +150°C. Since only 3 display digits are used (one after the decimal point), this circuit can measure temperature up to 99.9°C.

Since there are 8 ADC channels, more than one LM35 can be connected to the MCU for measuring temperatures at various places. A switch connected to RA0 input is used to display the temperature measured by these Sensors. The specified absolute error of A/D converter is < +/- 1 LSB for VDD = VREF. To meet this accuracy, the charge holding capacitor (internal to the chip) must be allowed to fully charge to input voltage level (approximately 20μs is required) before starting conversion.

Circuit Diagram:
 

Components Used:

1. Microcontroller :- PIC16C74A
2. Temperature Sensor :- LM35
3. Crystal Ocillator :- 4MHz
4. Comparator
5. Seven Segment Display
6. BJT :- PNP BC558
7. Resistors
8. Voltage source

Circuit Modification :-

This circuit can be modified and may be add the following features:

1. PC interface to log data.
2. Interface to control devices as per the temperature.
3. Audible warning such as buzzer or alarm when a set point temperature is reached.
4. Interfacing 4x4key board to input the data.
5. Crystal oscillator may be used according to the frequency required.
6. PNP transistor can be used of different configuration.
7. Other MCU can be used which are cheaper than this one.
8. In place of seven segment display LCD can be used.

Application:-

It can also be used to ON/OFF various equipments depends on the temperature limit.

Electronic Siren Circuit

Introduction :

This is a compact electronic siren circuit based on three transistors. This circuit is suitable for incorporating with other alarm or siren projects such as burglar alarms, automatic factory sirens etc or a simple push to on alarm.

The electronic siren circuit given here is based on a complementary transistor pair consisting of Q2 & Q3 (BC557 & BC 37) wired as an Astable Multivibrator oscillator, which directly drives the speaker.

Working :

The transistor Q1 is used to provide a full charge on capacitor C2 when power is turned ON. When push button switch S1 is pressed , the capacitor C2 slowly discharges through resistor R8. This makes the circuit to oscillate at a low frequency that increases to a high frequency and kept indefinitely as the capacitor is fully discharged. When the switch P1 is released, the output frequency decreases slowly as C2 is charged to the positive voltage through resistance R6 and the Base-Emitter junction of transistor Q2. When C2 is fully charged to the positive battery voltage the circuit stops oscillating.

Circuit diagram :

Component Used :

• NPN transistor BC337
• PNP transistor BC557
• 12V Battery
• Resistance
• Capacitors
• SPST switches
• Speaker 8 Ohm

Modifications :

• A 12 V battery or a a well regulated 12V DC power supply can be used to power the circuit.
• The switch S1 can be used to activate the alarm.
• The switch S2 can be used as a power switch.
• Tone of alarm can be changed by using different values for C2 and R8.

Electronic Toss Circuit

Introduction :

The circuit given here can be used for tossing head or tail. There are many games in which a tossing is required to start and this circuit can be used in all such instances.

Working :

The circuit uses two ICs NE 555 timer (IC1) and 74LS76 dual JK flip flop (IC2).The IC 1 is wired as an astable multi vibrator operating at 10Hz.The output of IC1 is inverted by using the transistor Q1.The collector of Q1 is connected to the pin 1 of IC2 via the push button switch S1.The IC2 is wired in toggle mode. When push button S1 is pressed the output pins 14 and 15 of IC2 starts toggling in state. The LEDs connected to these pins also toggles (Since the frequency of toggling is 10Hz, we feel both LEDs glowing).When push button S1 is released either one of the LED remains ON indicating the head or tail.

Circuit Diagram :

Components Used :

• NE 555 timer IC
• NPN transistor BC 548
• 74LS76 dual JK flip flop
• LEDs
• Resistors
• Capacitors
• Push Button Switch
• 5V Battery

Modification :

• The circuit can be powered from 9 V DC.
• Switch S1 is a push button switch, which can be replaced by SPST Switch.
• Capacitors can be used of having voltage rating upto 25 V.
• Electronic toss circuit can be made by CD4017 decade counter.

Mini efficient coil launcher from disposable camera flash

Introduction :

This is a fun and non-dangerous project for those people who like to throw projectiles magnetically. It simply works by placing a ferromagnetic projectile at one end of a coil and pulsing some power in it. The trick is to switch off power when the projectile is at the middle of the coil, there are some ways to do it but it isn't important now.

The second trick is to use a coil as close as possible to projectile to maximize coupling and the third to avoid saturation, that means keeping the current not to high.
For first you need some disposable camera flashes. You need 4 of more of them. Desolder the caps and collect them. They have ratings of 330V 120-160uF and can survive pulses up to 300A (each), or even dead shorts (but don't do it because it is quite a bang).

Circuit Diagram :

Working: :

The resistance is 350 milliohm and inductance is 165 uH (according to my LCR meter) giving a pulse lenght of 1 ms (Multisim simulation) and peak current of 400A, limited by inductance. Using more caps would increase pulse current because the resistance is low and the current is Inductance-limited, so i advice to use only 4 caps (maximum 5).

Concerning the switching 2N6509 SCRs (Onsemi) (25A 800V) which have a pulse rating of 300A x 6 ms (450 x 1ms). They are very good cheap and small and requires small signal to drive. A reverse diode was added to the caps because the simulations showed a peak reverse voltage in capacitors (it is an undamped LCR circuit) that could damage them. This solution limits reverse charging (to -0.5 V to 1V) and makes the current decay better reducing the such-back effect. The projectile is a 2.5 mm diameter nail with the same lenght as the winding.

Components Used :

• Voltage regulator LM324
• SCR 2N6509
• Diode
• 6V Battery
• Capacitors
• Resistors
• Inductor

Modifications :

• Another suitable SCR may be used in the place of 2N6509.
• Camera flash may be of any type but battery will be of rating corresponding to that.

Musical Car Reverse Horn Circuit

Introduction :

Here is a circuit that produce a musical horn when ever a car is in reverse gear. The circuit uses two ICs for the operation, voltage regulator 7805(IC1) and musical tone generator UM66(IC2). The IC1 reduces the car battery voltage to 5V. The diodes D1 & D2 in combination produces an additional drop of 1.4 V to give a 3.6 V supply for the UM66. The supply voltage of UM 66 should not be more than 4V. When ever the car is in reverse gear, the reverse gear switch of the car gets activated and the circuit gets connected to the car battery. The UM66 starts playing the music tone. The transistor T1 amplifies the output of UM66 to drive the loudspeaker.

Circuit diagram : 

Components Used:

• Voltage Regulator 7805
• Musical Tone Generator UM66
• 3 Diodes 1N4007
• 10V Battery
• 3 Capacitors 0.1,100,1uF
• 2 Resistors 100,100 Ohms
• NPN transistor BEL187
• Speaker 8 Ohm

Note:

• Place the circuit on a waterproof place in the dashboard.
• The switch S1 is the reverse gear switch of the car.
• A wrong connection may damage the car’s electrical circuit.
• The transistor Q1 is not very specific. Any medium power NPN audio transistor can be used.

Advantage :

This circuit will avoid the chances of accident at blind turn, as speeding vehicle get a alert by hearing the musical sound that a car is taking reverse and he will slow its speed.

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Parking Sensor Circuit

Introduction :

This simple circuit can be used as an aid for sensing the distance between the rear bumper of the car and any obstacle behind the car. The distance can be understood from the combination of the LEDs (D5 to D7) glowing. At 25cm D7 will glow, at 20 cm D7&D6 will glow and at 5cm D7, D6 and D5 will glow. When the obstacle is beyond 25 cm none of the above LEDs will glow.

Working :

Two ICs are used in the circuit. The IC1 (NE555) is wired as an Astable Multivibrator for driving the IR Diode D1 to emit IR pulses. The operating frequency of the transmitter is set to be 120Hz. The IR pulses transmitted by D1 will be reflected by the obstacle and received by the D2 (IR photo diode). The received signal will be amplified by IC2a. The peak of the amplified signal will be detected by the diode D4 and capacitor C4.R5 and R6 compensates the forward voltage drop of D4. The output voltage of the peak detector will be proportional to the distance between car’s bumper and obstacle. The output of peak detector is given to the inputs of the other three comparators IC2b,IC2c and IC2d inside the IC2 (LM324). The comparators switch the status LEDs according to the input voltage their inverting inputs and reference voltages at their non inverting inputs. Resistances R7 to R10 are used to set the reference voltages for the comparators.

Components Used :

• Astable Multivibrator using NE555 IC
• Comparators LM324 IC2b,IC2c and IC2d & IC2
• Diodes 1N4148
• LEDs
• 12V Battery
• Capacitors
• Resistors
• Photo Diode

Circuit Diagram :

Notes :

• The D1 & D2 must be mounted close (~2cm) to each other, looking in same direction.
• The D1 can be a general purpose IR LED.
• The D2 can be general purpose IR photo diode with sun filter.
• The transmitter as well as receiver can be powered from the car battery.
• For proper working of the circuit, some trial and error is needed with the position of D1 and D2 on the dash board.
• All capacitors must be rated 25V.
  
  
  
  
  

  Police Lights using 555 Timer

  
  
  

  Introduction :

  This circuit simulates the police car lights by alternate flashing. This circuit flashes red LEDs for three times and blue LED’s for three times. This flashing action performs continuously.

  This circuit uses 555 timer and a decade counter. Here, 555 timer runs in astable mode. Decade counter 4017 counts the incoming pulses that is for first pulse Q0 becomes high and for second pulse Q1 becomes high and so on again for 10th pulse Q0 state becomes high.

  Working :

  Here 555 timer produces continuous pulses via pin 3. The width of these pulses can be varied by varying the resistance (R1,R2 ) or capacitance (C1). These pulses are given as input to the decade counter. For every incoming pulse the output state of the decade counter is get incremented.

  • For 1st pulse – Q0 high – blue led’s glow
  • For 2nd pulse – Q1 high (no connection) – all led’s off
  • For 3rd pulse – Q2 high – blue led’s glow
  • For 4th pulse – Q3 high – all led’s off
  • For 5th pulse – Q4 high – blue led’s glow
  • For 6th pulse – Q5 high – red led’s glow , blue led’s off
  • Hence blue led’s flashes for 3 times.
  • For 7th pulse – Q6 high – all led’s off
  • For 8th pulse – Q7 high – red led’s glow
  • For 9th pulse – Q8 high – all led’s off
  • For 10th pulse – Q9 high – red led’s glow
  • For 11th pulse – Q0 high – blue led’s glow, red led’s off

  Hence red LEDs flash for 3 times. This process repeats continuously.

  Circuit Diagram :

  

  Components Used :

  • NE555 timer
  • 4017 decade counter
  • 1n4148 diodes – 6
  • 1k Resistor(1/4 watt) – 1
  • 22k Resistor(1/4 watt) – 1
  • 470 ohm Resistor(1/4 watt) – 8
  • 2.2uF Electrolytic capacitor(16V) – 1
  • Blue LED’s – 2
  • Red LED’s – 2
  • 9v battery – 1
  • Connecting wires

  Applications:

  • This circuit used as an indicator for police cars.
  • We can use it as LED flasher circuit by making some modifications.

  Note :

  • The values of the resistors R1, R2 and capacitor C1 should be same to get perfect flashing.
    
    
    
    

    Rain Alarm Circuit

    Introduction :

    Water is basic need in every one’s life. Saving and proper usage of water is very important. Here is an easy project which will give the alarm when there is rain, so that we can make some actions and save the rain water. As a result, we can increase the water levels of underground water by using underwater recharge technique. Rain water detector will detect the rain and make an alert; rain water detector is used in the irrigation field, home automation, communication, automobiles etc. Here is the simple and reliable circuit of rain water detector which can be constructed at low cost. Rain water sensor is the main component in the circuit.

  
  

  

  If there is no rain, the resistance between the wires will be very high and there will be no conduction between the wires in the sensor. If there is rain, the water drops will fall on the rain sensor which will also decrease the resistance between the wires and wires on the sensor board will conduct and trigger the NE555 timer through the transistors circuitry. Once NE555 is triggered, it will make the output pin high and which will make the buzzer to make alarm.

  Circuit Diagram:

  

  Working :

  • The points A and B of the circuit are connected to the points A and B of the rain sensor respectively. When rain is falling, the rain water will fall on the rain sensor which has aluminum wires on mica or Bakelite sheet. Due to the water on sensor, the aluminum wire ‘w’ develops resistance and gets conducted because of battery connector, the sensor and also to the circuit.
  • When the aluminum wires are connected, the transistor Q1will get turned on and make LED to glow and also Q2 will also be turned ON. When the Q2 is saturated, the capacitor C1 will be shorted and make the transistor Q3 to be turned ON. C1 will get charged by the resistor R4. The reset pin of 555timer which is connected to the emitter of Q3 will be made positive when Q3 reaches to the saturation mode.
  • The 555 timer is configured in astable mode. When the reset pin of the 555 timer is made positive because of saturation mode of Q3, it will generate the pulse at the pin 3 and make speaker to ring alarm. Capacitor is connected in between the pin 3 of 555 timer and speaker because to block the DC signal and allow only the variations in the signal which make the speaker to make sound. The diode D2 will not allow any reverse current from the timer.
  • Because of the resistor R4 and capacitor C1, Q3 will get in cut-off after sometime and make the reset pin of 555timer in negative and speaker will stops making sound. The time for 555timer to make speaker sound depends on the values of C1 and R4.
  • When there is no rain, the aluminum wire of the sensor will not have any resistance or conduction cannot trigger the circuit.

  
  

  Components Used :

  
  

  • NE555 IC
  • NPN transistor BC148
  • Speaker 8Ohm
  • Diode 1N4148
  • Capacitor
  • Resisotor

  
  

  Applications :

  • In the irrigation, it will detect the rain and immediately alert the farmer.
  • In automobiles, when the rain detector detects the rain it will immediately active the wipers and inform to the driver.
  • In communications, it will boost the power of the antenna and increase the signal strength to send or receive the signals.
  • This can also be used if there is a chemical rain also. This is very common in industrial areas.
    
    
    
    
    
    

  Water Level Controller Circuit

  
  

  Introduction :

  A simple but very reliable and effective water level controller circuit diagram is shown here. The circuit uses 6 transistors, 1 NE555 timer IC, a relay and few passive components. The circuit is completely automatic which starts the pump motor when the water level in the over head tank goes below a preset level and switches OFF the pump when the water level in the over head tank goes above the full level.

  
  

  Working :

  
  

  
  
  Probe D is positioned at the bottom level of the tank while probes A, B and C are placed at full, half and medium levels of the tank respectively. The level sensing part of the circuit is built around transistors Q1, Q2 and Q3. When water level is below the quarter level probes A, B and C are open and the transistor Q1, Q2 and Q3 remains OFF. When the water level rises and touches the probes the corresponding transistors gets biased and switches ON. Resistors R1, R2, R3 limit the bases current of corresponding transistors while resistors R4, R5, R6 limit their collector current. LEDs D1, D2 and D3 provide a visible indication of the current water level.
  
  When the water level goes below medium, transistor Q2 gets switches OFF and its collector goes positive. Collector of Q2 is connected to the base of transistor Q6 and as result transistor Q6 gets switched ON. Transistor Q5 will be also ON because its base in connected to the collector of Q4 which is presently OFF. As a result when the water level goes below medium relay K1 gets energized and the pump is driven. The relay is wired in the latching mode so that even if the water level goes above medium level the pump remains ON so that the tank gets completely filled. For wiring the relay in latching mode one set of N/O contacts is used. When relay is activated these contacts close which forms a short across collector and emitter of Q6. This makes the state of Q6 irrelevant to the operation of the relay and the relay remains ON as long as the transistor Q5 is ON. The only way to make the relay OFF is by switching OFF Q5 and it is done automatically when the water level reaches the full level.
  
  Collector of transistor Q1 is connected to the trigger pin (pin2) of IC1. When the water level reaches full level the transistor Q1 gets switched ON. As a result its collector goes to ground level which triggers the IC1 which is wired as a monostable. The output of IC1 goes high for about 1S. This makes the transistor Q4 ON for the same time and transistor Q5 whose base is connected to the collector of Q4 is switched OFF cutting the supply to the relay. This makes the motor OFF and it remains OFF until the water level again goes below the medium level.
  
  Resistor R8 is a pull up resistor for the trigger pin of the NE555. Capacitor C3 couples the collector of Q1 to the trigger pin of NE555 and facilitates edge triggering whenever the transistor Q1 goes ON. A monostable circuit can be made edge triggered by connecting the trigger signal to the trigger input pin through a capacitor. The capacitor blocks DC and passes sudden changes. The circuit used here is termed as negative edge triggered because the monostable is triggered when ever the trigger input signal falls. R10 and R12 limits the collector current of Q4 and Q5 respectively while R9 and R11 limits their base current. R13 limits the base current of Q6 while D4 is a freewheeling diode which protects the switching transistors from voltage transients.
  
  

  Circuit Diagram :

   

  

  Modification :

  
  

  • Use 12V DC for powering the water level controller circuit.
  • The relay used was a 5V/220 ohm relay and that’s why the current limits resistor R12 was added in the circuit. If a 12V relay is used then the R12 can be shorted.
  • K1 must be a double pole relay.
  • The load current, voltage ratings of the relay must be selected according to the ratings of the pump motor.
  • The type number of the transistors used are not very critical and can do suitable replacements if any type number is not available.