Door alarm for Fridge

This circuit will help you to save your electricity bill.  Incase if you leave the fridge door open more than twenty seconds. The circuit consumes very little current as it can operates by a 3 volts battery. You can enclose this whole circuit in a small box and keep inside the fridge.

R2 is a photo resistor. Normally photo resister has a low resistance but when you close the fridge door, with the darkness the photo resister’s resistance will go high. When you open the door fridge lamp will light and photo resister’s resistance goes down.

 Then the IC1 start its action. You can set the preset according to your wish but in this circuit it is set for 20 seconds delay. After 20 seconds the piezo starts beeps until you close the door.

Remember not to place the alarm box inside the freezer try to place it near the lamp.

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RING BELL ELECTRONIC CIRCUIT USING NE555 DIAGRAM

RING BELL ELECTRONIC CIRCUIT USING NE555 DIAGRAM

This circuit produces oscillating frequency around 1kHz, and able to be converted by changing the value of resistor R1. The speaker will produce a long beep sound with 1kHz frequency. Here is the schematic :

Parts list :

•     Resistor R1 : 10k ohm
•     Resistor R2 : 56k ohm
•     Capacitor C1-C2 : 0.01 uF
•     Polar capacitor C3 : 1 uF/15V
•     IC timer : NE 555
•     Speaker : 8 ohm 0.5 W
•     ON/OFF switch
•     5-15V Power supply

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AFX Slot Car Lap Counter

AFX slot car sets are very enjoyable but you can increase the fun with a lap counter. This circuit will count from 00 to 99, with independent counters for each track. The sensing device used is a Hall effect sensor (UGN3503; available from Dick Smith Electronics). One of these sensors is glued under a section of each track (printed side up); between the slot and one of the track rails is the best spot. In this position, it will allow the ground effects magnets on the cars to pass over them. The sensor will provide a voltage of about 3V when a car passes over it and about 2V without a magnetic field. Both counter circuits are identical, with dual op amp IC5 handling the signals from both sensors.

Circuit diagram:

 AFX Slot Car Lap Counter Circuit diagram

IC5a and IC5b are wired as comparators, with a 2.5V reference derived from zener diode ZD1 via the 10kO and 12kO resistors. Each time the output of IC5a goes high it clocks IC1a, a 4518 BCD counter. NAND gates IC2a & IC2b provide a carry out to the other half of IC1 for a 2-digit display. More counters may be cascaded this way to provide extra digits. The BCD outputs of IC1 drive 7-segment decoders IC3 & IC4 which drive common cathode LED displays. Push-button S1 resets the counters to 00 for both tracks for the start of a new race.

Author: Placid Talia - Copyright: Silicon Chip Electronics

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