Friday, November 2, 2012

Freeze Protector Circuit

This is the simple freeze protector circuit diagram. It is also called timing circuit. It is just hobby project for beginners. When you need to operate automatically any device in the fixed time later after coming AC power supply, you can use this circuit. 

The voltage amplitude is high when AC power come. Suddenly high voltage destroys the electronics device. For this reason, in the time of load shedding we need to switched off electronics device (Audio/Video player, CD/DVD Player, TV, Freeze or any electronics device). This circuit solve this problem.

Hobby Electronics helps the beginners to know the timing circuit specially using 555 IC timer. NE555 IC is the very simple well known parts. Its configuration is very simple. You can use this timer any simple circuit. 

In this circuit use 12volt power supplies. 300k variable resistor is used for timing control. Timing resistor and capacitor are 300k and 1000uF. Only change the value of the variable resistor for your required timing. 

The circuit output pin 3 is connected with resistor (10k) and output 12 volt relay. Relay is connected as figured with the device. Making cost is too low. Anyone can make this circuit easily.
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Complete Room Securty System Circuit diagram

This simple circuit is called room security system circuit. The main purpose of this circuit is to secure your room in night. You need not any security guard. When any unwanted person wants to enter your room in night then this circuit raised alarm. On the other benefit, it is always activated on load shedding.

There are five separates parts in this circuit – regulated power supply, relay driver, door switching, alarm system and audio amplifier. First section is regulated power supply. The output of IC 7809 is regulated +9Volt which is converted from 9Volt unregulated power supply. Capacitors are used for removing ripple. A full wave 9 volt transformer is connected in the input of this power section.

The second part is relay driver. Q1 transistor is used for driving relay. When the Q1 transistor is forward bias then the relay is ON and the total circuit gets positive voltage from ac source. In the time of load shedding relay is deactivated and the total circuit gets power from 6Volt Battery.

The third part is door switching. When C1 capacitor’s two terminals are short, transistor Q2 is reversed biased. So Q2 transistor is OFF. When C1 capacitor’s two terminals are open, transistor Q2 is forward biased. So Q2 transistor is ON. For this reason IC UM66 is ON and it generates music which is feed another two transistors Q3 and Q4. A speaker is connected with collector of the transistor Q4 as circuit diagram.
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Automatic Street Light Controller Circuit Diagram

This circuit is an automatic street light controller. Sensors used to detect changes in light is LDR (Light dependent resistor), the working principle of Light dependent resistor is exposed to light when the resistance value of LDR great, but if not exposed to light or dark then the resistance value of LDR.

LDR is a special type of resistance whose value depends on the brightness of the light which is falling on it. It has resistance of about 1 mega ohm when in total darkness, but a resistance of only about 5k ohms when brightness illuminated. It responds to a large part of light spectrum.
When light falls on the LDR then its resistance decreases which results in increase of the voltage at pin 2 of the IC 555. IC 555 has got comparator inbuilt, which compares between the input voltage from pin2 and 1/3rd of the power supply voltage. When input falls below 1/3rd then output is set high otherwise it is set low. Since in brightness, input voltage rises so we obtain no positive voltage at output of pin 3 to drive relay.
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Mobile Incoming Call Indicator Circuit Diagram

this circuit can be used to escape from the nuisance of mobile phone rings when you are at home. This circuit will give a visual indication if placed near a mobile phone even if the ringer is deactivated.


When a call is coming to the mobile phone, the transmitter inside it becomes activated. The  frequency of the transmitter is around 900MHz.The  coil L1 picks up these oscillations by induction and feds it to the base of Q1. This makes the transistor Q1 activated.Since the Collector of Q1 is connected to the pin 2 of IC1 (NE555) , the IC1 is triggered to make the LED connected at  its output pin (pin 3) to blink. The blinking of the LED is the indication of incoming call.
Notes:
  •    The coil L1 can be made by making 150 turns of 36 SWG enameled copper wire on a 5mm dia   plastic former.Or you can purchase a 10 uH coil from shop if available.
  •     The circuit can be powered from a 6V battery.
  •     Assemble the circuit on a good quality PCB.
  •     C1 & C3 are to be polyester  capacitors.
  •     The electrolytic capacitor C2 must be rated 10V.
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4017 LED Knight Rider Running Light Circuit Diagram

In this  4017 Knight Rider circuit, the 555 timer is wired as an oscillator. It can be adjusted to give the desired speed for the display. The output of the 555 is directly connected to the input of a Johnson Counter (CD 4017).
 The input of the counter is called the CLOCK line. The 10 outputs become active, one at a time, on the rising edge of the waveform from the 555. Each output can deliver about 20mA but a LED should not be connected to the output without a current-limiting resistor (220Ω in the circuit above).

The first 6 outputs of the chip are connected directly to the 6 LEDs and these “move” across the display. The next 4 outputs move the effect in the opposite direction and the cycle repeats. The animation above shows how the effect appears on the display. Using six LEDs, the display can be placed in the front of a model car to give a very realistic effect. The outputs can be taken to driver transistors to produce a larger version of the display.
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Digital Object Counter using LDR and digital IC 7490

This is the simple circuit on Hobby Electronics. In this circuit three modules are used in object counter. 555 timer are used as a monostable mode and astable mode. The other is counter module. In this circuit 555 timer configured as a monostable mode, is a simple automatic dark sensor circuit that gives output when light falling is blocked on LDR. Pin 3 of monostable circuit has been connected to pin 4 of astable timer. When monostable circuit generates output, astable mode timer starts giving pulses to the counter module. Frequency for counter module is set up using R4, R3 and C2.
7490acts as a decade counter and 7447 uses the output of 7490 to display numbers on seven segment display. This circuit counts from 0 to 9. You can count 0 to 100 modifying counter module circuit. Just adding few components as well as two counter ic, two display driver and two display. For count 0 to 100, comments on the comments box. You will get complete circuit.
The output will be: If you block light falling on LDR, the number on seven segment display will increase.
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A Small project on Battery level Indicator

Working principle of this circuit is battery voltage compared with the reference voltage. This circuit is constructed by using 741 op-amp ICs. Op-amp is differential amplifier which output will be positive or negative, depends on the difference of input voltages. When the input voltage difference is positive with respect to reference voltage and battery voltage, then the output is positive and the LED will emit light. If negative LED cannot emit light. It is the main principle of battery level indicator. Voltage level indicated by the column of LEDs. For easy of reading LED rearranged in a vertical array.

The top four LEDs indicates the battery voltage is high. Sequentially the lower level indicates the battery voltage is low and bottom four LEDs indicates very low voltage of the battery. So, if the battery voltage continues to decline then LEDs will die in sequence from top to bottom. In this circuit 1mA current is adjusted for reference voltage. Vcc is divided by the total number of resistor for finding the value of resistor R. On the other hand, the resistor value of R1 is calculated by the equation, Component:

1. Op-amp IC 741

2. R = 3kΩ

3. R1 =220kΩ

4.  Diode

Operation:

The voltage drop against the each resistor is 3 volt.

So when the Vin = 0v or less than 3v the output of all op-amp are at

–Vsat . The silicon diodes protect the light emitting diodes against excessive reverse bias voltage.

When Vin is increased to a value 3v to 6v, only the output of op-amp#1 goes positive  to light which indicate “Very Low”.

When Vin is increased to a value 3v and 6v, the output of op-amp#1 and  op-amp#2  are at +Vsat  and goes positive to light which indicate “Low”.

When Vin is increased to a value 6v and 9v, the output of op-amp#1, op-amp#2 and op-amp#3 are at +Vsat  and goes positive to light which indicate “Medium”.

Similarly, when Vin increased to 12v or higher, the output of all op-amps are at +Vsat  and all op-amps output goes positive to emit light of all LEDs which indicate “Full” .
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