{"id":1985,"date":"2014-01-21T23:17:57","date_gmt":"2014-01-21T21:17:57","guid":{"rendered":"http:\/\/www.devrearsiv.com\/?p=1985"},"modified":"2014-01-21T23:17:57","modified_gmt":"2014-01-21T21:17:57","slug":"fridge-door-alarm-circuit","status":"publish","type":"post","link":"https:\/\/devrearsivi.com\/fridge-door-alarm-circuit\/","title":{"rendered":"Fridge Door Alarm Circuit"},"content":{"rendered":"<p>This fridge door alarm is using a 3V battery supply should be placed (in a small box) in the fridge near the lamp or close to the opening. With the door closed the photo resistor R2 presents a high resistance (&gt;200K) thus clamping IC1 by holding C1 fully charged across R1 and D1.<\/p>\n<p>When a beam of light enters from the opening, or the fridge lamp lights, the photo resistor lowers its resist<img decoding=\"async\" class=\"alignright\" alt=\"fridge\" src=\"http:\/\/www.devrearsiv.com\/wp-content\/uploads\/2014\/01\/fridge.jpg\" width=\"150\" height=\"150\" \/>ance (&lt;2K) stopping C1 charging current. Therefore IC1, wired as an astable multivibrator, starts oscillating at a very low frequency and after a period of about 24 sec. its output pin (#3) goes high, enabling IC2.<\/p>\n<p>This chip is also wired as an astable multivibrator, driving the Piezo sounder intermittently at about 5 times per second. The alarm is activated for about 17 sec. then stopped for the same time period and the cycle repeats until the fridge door closes.<br \/>\n<em>Some notes for the fridge door alarm:<\/em><\/p>\n<ul>\n<li>Delay time can be varied changing C1 and\/or R3 values.<\/li>\n<li>Beeper repetition rate can be varied changing C2 and\/or R4 values.<\/li>\n<li>Stand-by current drawing: 150\u00b5A.<\/li>\n<li>Place the circuit near the lamp and take it away when defrosting, to avoid circuit damage due to excessive moisture.<\/li>\n<li>Do not put this device in the freezer.<\/li>\n<\/ul>\n<h2>Fridge door alarm circuit diagram<\/h2>\n<p><a href=\"http:\/\/www.devrearsiv.com\/wp-content\/uploads\/2014\/01\/fridge.jpg\"><a href=\"http:\/\/www.devrearsiv.com\/wp-content\/uploads\/2014\/01\/fridge-door-alarm.png\"><img decoding=\"async\" class=\"size-medium wp-image-1987 aligncenter\" alt=\"fridge-door-alarm\" src=\"http:\/\/www.devrearsiv.com\/wp-content\/uploads\/2014\/01\/fridge-door-alarm-300x149.png\" width=\"300\" height=\"149\" srcset=\"https:\/\/devrearsivi.com\/wp-content\/uploads\/2014\/01\/fridge-door-alarm-300x149.png 300w, https:\/\/devrearsivi.com\/wp-content\/uploads\/2014\/01\/fridge-door-alarm.png 523w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><\/a><\/a><\/p>\n<p>&nbsp;<\/p>\n<p><strong>Components Values<\/strong><br \/>\nR1 = 10K 1\/4W Resistor<br \/>\nR2 = Photoresistor (any type)<br \/>\nR3 = 2M2 1\/4W Resistor<br \/>\nR4 = 1M 1\/4W Resistor<br \/>\nC1= 10\u00b5F 25V Electrolytic Capacitor<br \/>\nC2 = 100nF 63V Polyester Capacitor<br \/>\nD1 = 1N4148 75V 150mA Diode<br \/>\nIC1, IC2 = 7555 or TS555CN CMos Timer ICs<br \/>\nBZ1 = Piezo sounder (incorporating 3KHz oscillator)<br \/>\nB1 = 3V Battery (2 x 1.5V AA, AAA or smaller type Cells in series)<\/p>\n","protected":false},"excerpt":{"rendered":"<p>This fridge door alarm is using a 3V battery supply should be placed (in a&#8230;<\/p>\n","protected":false},"author":1,"featured_media":1987,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[723],"tags":[729,1093,728],"aioseo_notices":[],"featured_image_urls":{"full":["https:\/\/devrearsivi.com\/wp-content\/uploads\/2014\/01\/fridge-door-alarm.png",523,261,false],"thumbnail":["https:\/\/devrearsivi.com\/wp-content\/uploads\/2014\/01\/fridge-door-alarm-150x150.png",150,150,true],"medium":["https:\/\/devrearsivi.com\/wp-content\/uploads\/2014\/01\/fridge-door-alarm-300x149.png",300,149,true],"medium_large":["https:\/\/devrearsivi.com\/wp-content\/uploads\/2014\/01\/fridge-door-alarm.png",523,261,false],"large":["https:\/\/devrearsivi.com\/wp-content\/uploads\/2014\/01\/fridge-door-alarm.png",523,261,false],"1536x1536":["https:\/\/devrearsivi.com\/wp-content\/uploads\/2014\/01\/fridge-door-alarm.png",523,261,false],"2048x2048":["https:\/\/devrearsivi.com\/wp-content\/uploads\/2014\/01\/fridge-door-alarm.png",523,261,false],"covernews-slider-full":["https:\/\/devrearsivi.com\/wp-content\/uploads\/2014\/01\/fridge-door-alarm.png",523,261,false],"covernews-slider-center":["https:\/\/devrearsivi.com\/wp-content\/uploads\/2014\/01\/fridge-door-alarm.png",523,261,false],"covernews-featured":["https:\/\/devrearsivi.com\/wp-content\/uploads\/2014\/01\/fridge-door-alarm.png",523,261,false],"covernews-medium":["https:\/\/devrearsivi.com\/wp-content\/uploads\/2014\/01\/fridge-door-alarm.png",523,261,false],"covernews-medium-square":["https:\/\/devrearsivi.com\/wp-content\/uploads\/2014\/01\/fridge-door-alarm.png",400,200,false]},"author_info":{"display_name":"Ferhat \u00c7elik","author_link":"https:\/\/devrearsivi.com\/author\/94ferhat\/"},"category_info":"<a href=\"https:\/\/devrearsivi.com\/category\/electronics-circuits\/\" rel=\"category tag\">Electronics circuits<\/a>","tag_info":"Electronics 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