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Freezer / Frost Alarms
 

Last Updated: October 18, 2017 05:04 AM


Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:

Circuits Designed by Dave Johnson, P.E. :

Alarm Sounds At Freezing TemperaturesThis electronic hobby circuit below is designed to activate a beeper alarm, whenever the outside air temperature is below 0 degrees C   (32F) .  A 9v battery powers the hobby circuit.  The average 9ua current is so low that the battery should last for many years . . . Hobby Circuit designed by Dave Johnson P.E.-July, 2006

Battery-Powered Freezer AlarmA typical freezer can contain hundreds of dollars with of food.  If the device becomes unplugged or if the door is left open too long, the food inside can quickly become spoiled.  The hobby circuit below is a battery powered alarm system, which is attached . . . Hobby Circuit designed by David Johnson P.E.-July, 2006

Freeze AlarmI chose an accurate thermistor from Keystone as the temperature sensor for this circuit.  This device has a very specific resistance at a particular temperature.  According to the data sheet for the thermistor, the device will have a resistance of 361K at zero degrees C, which is the freezing point of water.  The thermistor is wired into a simple bridge circuit, which uses 1% resistors.  The bridge is connected to a very low power voltage comparator.  The circuit forms a switch circuit, which changes state, when the resistance of the thermistor reaches a certain value.  At zero degrees C the voltage at the non-inverting input of the comparator exceedsCircuit Solution by Dave Johnson P.E.-May, 2006

Freezer Over-Temperature AlarmThis circuit turns on a beeper whenever the inside temperature of a freezer is greater than zero degrees Centigrade.  The circuit draws only a few microamps from a 9 volt battery.  It uses a glass bead thermistor accurate to 1 degree C.. . . Circuit by Dave Johnson P.E.-November, 2014

Freezing Temperature AlarmThe circuit below is designed to activate a beeper alarm, whenever the outside air temperature is below 0 degrees C (32F).    A 9v battery powers the circuit.    The average 9ua current is so low that the battery should last for many years.. . . Circuit by David Johnson P.E.-November, 2014

Alarm Sounds At Freezing Temperatures -  This electronic hobby circuit below is designed to activate a beeper alarm, whenever the outside air temperature is below 0 degrees C   (32F) .  A 9v battery powers the hobby circuit.  The average 9ua current is so low that the battery should last for many years . . . Hobby Circuit designed by Dave Johnson P.E.-July, 2006

Battery-Powered Freezer Alarm -  A typical freezer can contain hundreds of dollars with of food.  If the device becomes unplugged or if the door is left open too long, the food inside can quickly become spoiled.  The hobby circuit below is a battery powered alarm system, which is attached . . . Hobby Circuit designed by David Johnson P.E.-July, 2006

Cold Activated Switch -  The thermistor used has a resistance of 15k at 25 degrees and 45k at 0 degrees celsius.  A suitable bead type thermistor is found in the Maplin catalogue.  The 100k pot allows this circuit to trigger over a wide range of temperatures. __ Designed by Andy Collison

Freeze Alarm -  I chose an accurate thermistor from Keystone as the temperature sensor for this circuit.  This device has a very specific resistance at a particular temperature.  According to the data sheet for the thermistor, the device will have a resistance of 361K at zero degrees C, which is the freezing point of water.  The thermistor is wired into a simple bridge circuit, which uses 1% resistors.  The bridge is connected to a very low power voltage comparator.  The circuit forms a switch circuit, which changes state, when the resistance of the thermistor reaches a certain value.  At zero degrees C the voltage at the non-inverting input of the comparator exceedsCircuit Solution by Dave Johnson P.E.-May, 2006

Freezer Over-Temperature Alarm -  This circuit turns on a beeper whenever the inside temperature of a freezer is greater than zero degrees Centigrade.  The circuit draws only a few microamps from a 9 volt battery.  It uses a glass bead thermistor accurate to 1 degree C.. . . Circuit by Dave Johnson P.E.-November, 2014

Freezing Temperature Alarm -  The circuit below is designed to activate a beeper alarm, whenever the outside air temperature is below 0 degrees C (32F).    A 9v battery powers the circuit.    The average 9ua current is so low that the battery should last for many years.. . . Circuit by David Johnson P.E.-November, 2014

Fridge Alarm-Version 1 -  activated by the light in a fridge or freezer.  Sounds an alarm if the door is left open too long __ Contact: P. Townshend EduTek Ltd

Fridge Alarm-Version 2 -  this 10a MOSFET driver will power most small to medium power dc motors up to 24v __ Contact: P. Townshend EduTek Ltd

Fridge Door Alarm -  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 (>200K) thus clamping IC1 by holding C1 fully charged across R1 and D1.  When a beam of light enters from the opening,  __ Designed by Popescu Marian

Fridge door Alarm -  Beeps if you leave open the door over 20 seconds; 3V battery operation, simple circuitry __ Contact: Flavio Dellepiane, fladello @ tin.it

Fridge door Alarm (2nd Version) -  Alternative version of the popular circuit; 3V battery supplyStill operating at 1.3V __ Contact: Flavio Dellepiane, fladello @ tin.it

Fridge Saver Beats the Heat -  15-Sep-10 -Design News:   Do your kids, spouse, or friends take too much time scanning the contents of your refrigerator? Have your pets figured out how to open the door and keep it open for minutes at a time? You might need the Fridge Saver, a project created by Chris Popp to show how you can monitor a refrigerator--or __   Gadget Freak-Case #171

Frost Alarm -  The thermistor used has a resistance of 15k at 25 degrees and 45k at 0 degrees celsius.  A suitable bead type thermistor is found in the Maplin catalogue.  The 100k pot allows this circuit to trigger over a wide range of temperatures.  A slight amount of hysteresis is provided by inclusion of the 270k resistor.  This prevents relay chatter when temperature is near the switching threshold of this circuit __ Designed by Andy Collison

Open-door Alarm prevents accidental Defrosts -  1-Feb-07 EDN-Design Ideas Circuit helps save a lab freezer or temperature chamber's contents__ Circuit Design by Tom Lyons Fisher, Juniata College, Huntingdon, PA

Sensitive Freezer Alarm with Buzzer -  Here is a simple freezer alarm circuit, but ultra sensitive with a buzzer.  The circuit raises an audio alert when the temperature inside the freezer box goes up above a preset level.  The circuit requires 9V dc supply and can power from a standard 9V alkaline battery.  A negative temperature co-efficient type (NTC type) small __ Designed by T.K. Hareendran


Freezer / Frost Alarms

 


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