NE555 Rain Alarm Circuit

NE555 Rain Alarm Circuit

This circuit gives out an alarm when its sensor is wetted by water. A 555 astable multivibrator is used here which gives a tone of about 1kHz upon detecting water. The sensor when wetted by water completes the circuit and makes the 555 oscillate at about 1kHz.

The sensor is also shown in the circuit diagram. It has to placed making an angle of about 30 - 45 degrees to the ground. This makes the rain water to flow through it to the ground and prevents the alarm from going on due to the stored water on the sensor.

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Cmos Single Zone Intruder Alarm Circuit

This ambit appearance automated Exit and Entry delays - timed anxiety absolute - and arrangement reset. It has accouterment for normally-open and normally-closed switches - and will clothing all of the accepted ascribe accessories (Pressure Mats, Magnetic Reed contacts, Foil Tape, PIRs and Inertia-Sensors, see http://uk.geocities.com/ronj_1217/cmos_sza.html#is).

If the Green Led is not lighting - analysis for an accessible window or aperture etc. Once you're annoyed that the architecture is defended - and the Green Led is lighting - move SW1 to the "set" position. At this point - the Red Led will ablaze - and the Exit Delay will begin. The breadth of the Exit Delay is set by the amount of R12.

With a 220k resistor - you accept about 30 to 40 abnormal to leave the building. As you do so - the Buzzer will sound. It should stop aural if you abutting the aperture abaft you. This indicates that the actuate ambit has been auspiciously adequate aural the time allowed.

When you acknowledgment to the architecture and accessible the aperture - the Buzzer will complete - and the Entry Delay will begin. The breadth of the Entry Delay is set by the amount of R8. With a 470k resistor- you'll accept about 30 to 40 abnormal to move SW1 to the "off" position. If you abort to do so - the Siren will sound.

The breadth of time the Siren sounds is set by R11. With a 4M7 resistor it will complete for about 15 to 20 minutes. Then the broadcast will bead out - and the anxiety will attack to displace itself. It does this by application Q3 to about-face itself "off" briefly.

If the actuate ambit has been adequate - the anxiety will reset. If not - the attack will abort - and the anxiety will reactivate. It will go on aggravating to displace itself every 15 to 20 account - until either the actuate ambit is adequate - or the anxiety is switched off.

All the accepted triggering accessories may be affiliated to the ascribe terminals. These cover Inertia-Sensors. The acuteness of the Sensors is adapted by R4. Set to minimum amount - a ablaze tap will actuate the alarm. Set to best amount - a abundant draft is required.

If you are not application Inertia Sensors - alter R4 with a 220k anchored resistor. If you are not application normally-open switches - you can leave out R1, C1 & Q1 - but you have to fit an added hotlink amid the Green Led and C2.

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DS1307 Alarm Digital Clock Circuit

DS1307 Alarm Digital Clock Circuit Diagram

The circuit diagram for the digital clock. 2x16 LCD is connected to the port 2 of AT89C51. P1.0 of uC will provide the SCL (serial clock) and P1.1 SDA (serial data) for I2C communication.


There are four switches connected to the uC, as shown in the figure. Function of the keys are same as clear from their names.

When the power supply is switched on it will give you the default date and time, but later you can change it to the desired value. After setting once, the backup battery will keep the clock ticking even after the power is not there.

A little about I2C:
There are basically four main conditions in I2C protocol.
1) Start Condition
2)Stop Condition
3)Data Validity
4)Acknowledgement

1)Start Condition:
when SCL is high and SDA H->L, will be taken as start condition for the communication.
2)Stop Condition:
when SCL is high and SDA L->H, will generate a stop condition.
3)Data Validity:
When SCL is high there should be no chande in SDA line only then the data is valid, the data change should be made only when SCL is low.
4)Acknowledgement:
After sending of one byte of data the reciever has to acknowledge the sender for the successful reception. for this the sender make the SDA line high and reciever pulls down the SDA low, which tells the sender that data has reached safely.

Designer Contact : ajay_bhargav@hotmail.com

Source: www.kmitl.ac.th

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