Monday, April 8, 2013
Motion Sensor Switch Circuit for Alarm
Now install the PIR module hanging from a 3 meter high mast (to cover 10 meter radius area) and connect its supply and relay terminals to our finished and enclosed circuit, observing right polarity. A 4-core screened cable can be used for this interconnection. Power the circuit from a regulated 12VDC adaptor/solar power box.
Whenever the PIR module detect movement of a live body its relay output toggles and the switching mosfet (T1) in the circuit is switched to on via resistor R1 and related parts. As result, the EM relay at the output of T1 is activated and the electric sprinkler gets its supply through the relay (RLY1) contacts. This contacts (or spare contacts) can also be used to activate a high-power warning alarm.
Sunday, April 7, 2013
Heat Sensor Circuit
So when the room temperature is increased its resistance decreases
simultaneously and more current flows through the resistor and the
thermistor. We find more voltage at the junction of the resistor and the
thermistor.
thermistor resistance value is 110 ohms. Suppose the resistance value
becomes 90 ohms after heating the 110 ohms thermistor. Then the voltage
across one resistor of the voltage divider
circuit equals the ratio of that resistor’s value and the sum of
resistances of the voltage across the series combination. This is the
concept of voltage divider.
Emitter voltage is maintained at 4.7volt with the help of zener diode.
This voltage is used to compare voltage. Transistor conducts when base
voltage is greater than the emitter voltage. Transistor conducts if it
gets more than 4.7volt of base voltage. Then the circuit is completed
through buzzer and it gives sound.
Monday, March 25, 2013
A Simple Fog Lamp Sensor
For several years now, a rear fog lamp has been mandatory for trailers and caravans in order to improve visibility under foggy conditions. When this fog lamp is switched on, the fog lamp of the pulling vehicle must be switched of to avoid irritating reflections. For this purpose, a mechanical switch is now built into the 13-way female connector in order to switch of the fog lamp of the pulling vehicle and switch on the fog lamp of the trailer or caravan. For anyone who uses a 7-way connector, this switching can also be implemented electronically with the aid of the circuit illustrated here.
Circuit diagram:
Fog Lamp Sensor Circuit Diagram
Here a type P521 optocoupler detects whether the fog lamp of the caravan or trailer is connected. If the fog lamp is switched on in the car, a current flows through the caravan fog lamp via diodes D1 and D2. This causes the LED in the optocoupler to light up, with the result that the photo-transistor conducts and energies the relay via transistor T1. The relay switches of the fog lamp of the car. For anyone who’s not all thumbs, this small circuit can easily be built on a small piece of perforated circuit board and then fitted somewhere close to the rear lamp fitting of the pulling vehicle.
Author :Harrie Dogge Copyright :Elektor Electronics 2008