Wiring 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.

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. 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.

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.

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).

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.

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” .