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Temperature Alarm Circuits

Temperature Alarms:  #'s - M       O - Z
 

Last Updated: December 07, 2017 02:04 PM

Circuits Designed by Dave Johnson, P.E. :
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

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

 

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

2-Terminal Temperature-to-Current Thermometer Suitable for Use at the End of Long Wire Runs -  By adding the LT3092 to a thermistor kit along with three 0.1% accuracy resistors and one final trim, a very accurate 2-terminal temperature-to-current converter can be built.  This circuit measures 700μA operating current at 0C, dropping by 2μA every degree until 100C, at which point the current measures 500μA.  The obvious __ Linear Technology/Analog Devices App Note, Mar 16th 2011

A Temperature Sensor Control -  A basic circuit using Diodes to detect temperature differences __ Designed by G.L. Chemelec

A Thermostat Control for Electric Heaters -  One Advantage of these two units is the Sensor can be placed Away from the heater, therefore sensing the Actual Room temperature, not the direct heat from the heater.  These can also be used in a confined space with a Heat Lamp, to create a Drying Oven  __ Designed by G.L. Chemelec

Acoustic Thermometry Measures Temperature to 0.1 Degree -  Start Clock Launches Acoustic Pulse into Measurement Path, Sets Width Decode Flip-Flop High.  Acoustic Paths Return Pulse, Amplified by Receiver, Trips Trigger, Resetting Flip-Flop.  Resultant Q Width Output, Representing Paths Temperature Dependent Transit Time, is Converted to Temperature Reading by Microprocessor.  __ Linear Technology/Analog Devices App Note, Apr 29th 2011

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

An introduction to acoustic thermometry -  04/21/11  EDN Technical Article: Use an ultrasonic transducer to measure air temperature in an olive jar.   __ Circuit Design by Jim Williams, EDN's most revered contributor, passed away in June 2011 after a stroke.  He was 63.

AN131 - An Introduction to Acoustic Thermometry -  Linear Technology AN131 __ Designed by Jim Williams - Apr 26th, 2011

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

Bridge Reversal Eliminates 1/f Noise & Offset Drift of a Low Noise, Non-Autozeroed, Bipolar Amplifier -  This circuit gives 14nV noise level (or 19 effective bits) over a 10mV span.  Bridge reversal eliminates 1/f noise and offset drift of a low noise, non-autozeroed, bipolar amplifier.  The LTC2440 is a high speed 24-bit No Latency delta sigma ADC with 5ppm iNL and 5μV offset.  it uses proprietary delta-sigma architecture enabling __ Linear Technology/Analog Devices App Note, Jul 8th 2010

Complete Type K Thermocouple Measurement System (SPI) with Cold Junction Compensation -  The LTC2484 is ideal for direct digitization of thermocouples and other low voltage output sensors.  The input has a typical offset error of 500nV (2.5μV max) offset drift of 10nV/C and a noise level of 600nVRMS.  The only signal conditioning is a simple surge protection network.  in any thermocouple meter, the cold junction __ Linear Technology/Analog Devices App Note, Apr 8th 2010

Computer Voltage & Temperature Monitoring -  The LTC2991 is used to monitor system temperatures, voltages and currents.  Through the i2C serial interface, the eight monitors can individually measure supply voltages and can be paired for differential measurements of current sense resistors or temperature sensing transistors.  Additional measurements include internal temperature __ Linear Technology/Analog Devices App Note, Sep 7th 2011

Differential Bridge Amplifier -  The LTC2050HV are zero-drift operational amplifiersavailable in the 5- or 6-lead SOT-23 and SO-8 packages.  The LTC2050 operates from a single 2.7V to 6V supply.  The LTC2050HV operates on supplies from 2.7V to 5.5V.  The current consumption is 800μA and the versions in the 6-lead SOT-23 and SO-8 packages offer power shutdown __ Linear Technology/Analog Devices App Note, Apr 29th 2010

Differential Bridge Amplifier with Gain Programmed through the Serial Interface & Analog to Digital Conversion (Standby Current Less than 100μA) -  The LTC6915 is a precision programmable gain instrumentation amplifier.  The gain can be programmed to 0, 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, or 4096 through a parallel or serial interface.  The CMRR is typically 125dB with a single 5V supply with any programmed gain.  The offset is below 10μV with a temperature __ Linear Technology/Analog Devices App Note, Apr 29th 2010

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

Full-Bridge Amplification using a Resistor Arrays to Provide Precise Matching in Excitation Amplifier -  This example provide excitation using resistor arrays to produce precise gain.  The circuit is configured to provide 10V and 5V excitation to the bridge, producing a common mode voltage at the input to the LTC2430/LTC2431 of 2.5V, maximizing the AC input range for applications where induced 60Hz could reach amplitudes up __ Linear Technology/Analog Devices App Note, Apr 29th 2010

Full-Bridge Amplification using a Single Amplifier -  This example shows a single amplifier being used to produce single-ended gain.  This topology is best used in applications where the gain setting resistor can be made to match the temperature coefficient of the strain gauges.  if the bridge is composed of precision resistors, with only one or two variable elements, the reference __ Linear Technology/Analog Devices App Note, Apr 29th 2010

Full-Bridge Amplification using Autozero Amplifiers to Reduce Input Referred Noise -  This circuit shows an example of a simple amplification scheme.  This example produces a differential output with a common mode voltage of 2.5V, as determined by the bridge.  The use of a true three amplifier instrumentation amplifier is not necessary, as the LTC2430/LTC2431 have common mode rejection far beyond that of most __ Linear Technology/Analog Devices App Note, Apr 29th 2010

High Resolution Battery-Powered Robust Type K Thermocouple Signal Conditioning Amplifier with Cold Junction Compensation -  The circuit is used as a plug-in adapter for common digital multimeters and is completely portable.  This circuit employs the LT1025 thermocouple compensator to improve accuracy over a wide range of ambient conditions and is mounted close to the thermocouple connection points for optimal thermal tracking.  it precludes the need __ Linear Technology/Analog Devices App Note, Apr 8th 2010

High Resolution Type S Thermocouple Digitizer with Improved Cold Junction Compensation -  This simple interface circuit that demonstrates the practicality of direct thermocouple connection to the LTC2400 using low output voltage thermocouples (a Type S thermocouple, as shown, produces a full-scale output voltage of 18mV).  This circuit uses the LT1025, a micropower thermocouple cold junction compensator, to sense __ Linear Technology/Analog Devices App Note, Apr 8th 2010

High Voltage/Current & Temperature Monitoring -  The LTC2990 is used to monitor system temperatures, voltages and currents. Through the i2C serial interface, the device can be configured to measure many combinations of internal temperature, remote temperature, remote voltage, remote current and internal VCC. The internal 10ppm/C reference minimizes the number of supporting components and area required. Selectable address and configurable functionality give the LTC2990 flexibility to be incorporated in various systems needing temperature, voltage or current data.__ Linear Technology/Analog Devices App Note, Oct 26th 2010

Internal Temperature Sensor -  The LTC2997 is a high-accuracy analog output temperature sensor. it converts the temperature of an external sensor or its own temperature to an analog voltage output.__ Linear Technology/Analog Devices App Note, Jul 7th 2011

Introduction to acoustic thermometry -  04/21/11  EDN Technical Article: Use an ultrasonic transducer to measure air temperature in an olive jar.   __ Circuit Design by Jim Williams, EDN's most revered contributor, passed away in June 2011 after a stroke.  He was 63.

Introduction to Acoustic Thermometry -  Linear Technology AN131 __ Designed by Jim Williams - Apr 26th, 2011

Kitchen Circuits -  Do your kids leave the door to the refrigerator open? Or does your celery reach out to keep the door from closing properly when you turn your back? Here's a simple circuit that beeps whenever the door is open for an extended period of time (which will also put a little pressure on the fridge loiterers in the house)  __  Contact:  Charles Wenzel of Wenzel Associates, Inc.

Linear Thermometer -  T1 has a built in pair of thermistors with linearizing resistors custom scaled for a specific temperature range.  , 0C to 100C in this example.  The flying capacitor LTC1043 eliminates any dc loading on the precision network to maintain linearity over the entire temperature range.  Amplifier gain is scaled to provide an output __ Linear Technology/Analog Devices App Note, Jun 21st 2011

Linearized Platinum Resistance Thermometer with 0.025C Accuracy Over 0 to 100C -  Platinum RTD's are typically driven with a constant current so that their resistance value directly translates to a temperature dependant voltage.  Here the LT1001 and the LM129 create a constant current through the input 10K resistor which all flows through the sense resistor.  A second amplifier inverts the signal to provide __ Linear Technology/Analog Devices App Note, Jun 21st 2011

Liquid-Level Indicator -  The LTC2990 is used to monitor system temperatures, voltages and currents.  Through the i2C serial interface, the device can be configured to measure many combinations of internal temperature, remote temperature, remote voltage, remote current and internal VCC.  The internal 10ppm/C reference minimizes the number of supporting __ Linear Technology/Analog Devices App Note, Mar 16th 2011

LTC2057 Differential Thermocouple Amplifier -  The LTC2057 is a high voltage, low noise, zero-drift operational amplifier that offers precision DC performance over a wide supply range of 4.75V to 36V or 4.75V to 60V for the LTC2057HV.  Offset voltage and 1/f noise are suppressed, allowing this amplifier to achieve a maximum offset voltage of 4μV and a DC to 10Hz input __ Linear Technology/Analog Devices App Note, Jun 19th 2013

LTC2990-Motor Protection/Regulation -  The LTC2990 is used to monitor system temperatures, voltages and currents. Through the i2C serial interface, the device can be configured to measure many combinations of internal temperature, remote temperature, remote voltage, remote current and internal VCC. __ Linear Technology/Analog Devices App Note, Oct 26th 2010

Micropower Thermocouple Signal Conditioner with Cold Junction Compensation -  A thermistor, shown as R3, is used to monitor the cold junction temperature.  its resistance becomes smaller as the cold junction temperature increases.  An increase in cold junction temperature will reduce the output voltage of the Type J thermocouple by 52uV/C.  The voltage reference and scaling of resistor values creates an __ Linear Technology/Analog Devices App Note, Jun 21st 2011

Motor Protection/Regulation -  The LTC2990 is used to monitor system temperatures, voltages and currents. Through the i2C serial interface, the device can be configured to measure many combinations of internal temperature, remote temperature, remote voltage, remote current and internal VCC. __ Linear Technology/Analog Devices App Note, Oct 26th 2010

Motor Protection/Regulation-LTC2991 -  The LTC2991 is used to monitor system temperatures, voltages and currents.  Through the i2C serial interface, the eight monitors can individually measure supply voltages and can be paired for differential measurements of current sense resistors or temperature sensing transistors.  Additional measurements include internal temperature__ Linear Technology/Analog Devices App Note, Sep 7th 2011

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Temperature Alarms:  #'s - M       O - Z


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