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Temperature Control Circuits

Temperature Controls:  #'s - F       G - S       T - Z
 

Last Updated: October 18, 2017 05:04 AM

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

Capacitance Proximity Switch
Draws very low power - Ideal for battery-powered applications
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Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:

2 Temperature Controlled Relays -  Switching Circuits:  These two circuits use Thermistors (Temperature Dependent Resistors).  Circuit No.1 energizes the relay when the temperature rises above a preset level. Use it to switch things on when it gets hot. Circuit No.2 energizes the relay when the temperature falls below a preset level. Use it to switch things on when it gets cold.  __ Designed by Ron J.

A New 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

Achieve Precision Temperature Control with TEC Seebeck-Voltage Sampling -  27-Nov-08 EDN Design Ideas:  By periodically setting the TEC's drive to zero, a storage capacitor samples and holds the Seebeck voltage __ Circuit Design by W Stephen Woodward, Chapel Hill, NC

ADC enables temperature-compensated weigh-scale measurements -  5-Jul-01 EDN Design Ideas:  You can provide temperature compensation in weigh-scale applications by simultaneously measuring both the temperature of the bridge and the primary output of the bridge transducer.  Traditionally, an integrated multiplexer connects multiple input variables to a single sigma-delta ADC.  Each time the multiplexer switches the input, the ADC must flush the digital filter of all data pertaining to t __ Circuit Design by Albert O'Grady, Analog Devices, Limerick, Ireland

ADC Helps Temperature-Compensate Transducer -  01/20/94 EDN Design Ideas:  You can use many tricks to make temperature-compensated resistive full-bridge transducers, such as piezoresistive pressure or strain-guage sensors.  Most of these tricks use some additional thermosensitive components that produce a compensating voltage or current.  The disadvantages of such solutions are obvious  low accuracy __ Circuit Design by Alexander L Belousov, Science Instruments Co, Baltimore, MD

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

Attenuators Nullify Temperature Deviations -  08/17/98 EDN Design Ideas:  NOTE:     FILE
has several circuits, scroll to this one.  You can use the circuits in Figure 1 to temperature-compensate a dc voltage of any circuit if the voltage-versus-temperature curve meets the following criteria:   The curve is stable in time at the same temperature;  The curve is reproducible under repeated temperature cycling;  The curve is monotonic within the necessary after-compensation accuracy (in other words, the curve doesn't have local fluctuations that exceed the maximum-allowable after-compensation flatness) ;
The curve has either a positive or negative slope or is C-shaped. __ Circuit Design by Semyon Lapushin, Electronic System Products, A Division of Antec, Norcross, GA

Auto-Fan, temperature control -  This circuit was designed to automatically activate a set of three or four small DC fans to cool a large cool-rib for a 10 Amp powersupply.  Can be used in a variety of other applications as well __ Designed by Tony van Roon  VA3AVR

Bang-bang thermostat is Simple Circuit & efficient -  11/06/97 EDN Design Ideas:  Perhaps  simplest and oldest feedback loop is  nonproportional, all-or-nothing, "bang-bang" rmostat.  Fully turning on a heater when  temperature is below setpoint and off when it's above setpoint is a straightforward example of a servomechanism.  Yet, elementary and crude as servomechanisms are, examples surround __ Circuit Design by W Stephen Woodward, University of North Carolina--Chapel Hill

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

Boost converter controls 12V fan from 5V supply -  12/12/97 EDN Design Ideas:  Temperature-controlled PWM boost converter allows operation of a12V brushless dc fan from a5V supply.    __ Circuit Design by John McNeill, Worcester Polytechnic Institute, Worcester, MA

Circuit Compensates Optocoupler Temperature Coefficient -  11/22/01 EDN Design Ideas:  When using an optocoupler in a linear application, you should consider its gain drift with temperature.  Traditional single- and dual-transistor-output devices have a notable gain drift with temperature.  in recent years, some temperature-compensated optocouplers have appeared.  However, another option is to use two optocouplers or a dual optocoupler with appropriate feedback to make the dri __ Circuit Design by J Michael Zias, Acme Electric Corp, Cuba, NY

Circuit controls multiple thermoelectric coolers -  08/19/99 EDN Design Ideas:  Optoelectronic and other components sometimes use a thermoelectric cooler and a thermistor for temperature control.  A typical thermoelectric cooler __ Circuit Design by Frank Effenberger

Circuit generates fan-speed control -  03/21/02 EDN Design Ideas:  Fan noise is becoming a significant issue as electronic equipment increasingly enters the office and the home.  Noise is proportional to fan speed, and the airflow¡ªhence, fan speed¡ªnecessary for cooling is less at low ambient temperatures.  Because ambient temperature is lower than the upper design point most of the time, a fan can run slower, making it easier on the ears __ Circuit Design by Jim Christensen, Maxim Integrated Products, Sunnyvale, CA

Circuit improves on temperature measurement -  05/02/02 EDN Design Ideas:  When current pulses with a stable iHiGH/iLOW ratio modulate a semiconductor junction, the ensuing voltage difference (for example, ΔVBE for a bipolar transistor] is a linear function of the absolute (Kelvin] temperature, T.  You can use this truism to make accurate temperature measurements.  Technical literature has thoroughly covered the relationship (references 1 to 4] and has numerou __ Circuit Design by Alexander Bell, Infosoft International Inc, Rego Park, NY

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.  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

Compensate for Optocoupler Temperature Coefficient -  11/22/01  EDN Design Ideas:  When using an optocoupler in a linear application, you should consider its gain drift with temperature.  Traditional single- and dual-transistor-output devices have a notable gain drift with temperature.  in recent years, some temper __ Circuit Design by J Michael Zias, Acme Electric Corp, Cuba, NY

Constant Temperature -  This circuit is a generic low power temperature controller that can be used for stabilizing temperature sensitive electronic circuits.  it was built to stabilize a radio frequency VFO (Variable Frequency Oscillator) for ham radio applications.  The circuit has also been used to lower the drift of a Ramsey FM10a micropower FM transmitter __ Designed by G. Forrest Cook

Control Multiple Thermoelectric Coolers -  08/19/99 EDN Design Ideas:  Optoelectronic and other components sometimes use a thermoelectric cooler and a thermistor for temperature control.  A typical thermoelectric cooler __ Circuit Design by Frank Effenberger

Controller provides closed-loop temperature regulation -  05/08/97 EDN Design Ideas:  Sometimes, you need to test a circuit element over temperature, but it's impossible to put the entire application circuit in the temperature chamber.  Freeze sprays and hair dryers are convenient for gross benchtop troubleshooting, but the temperature and slew rate are highly uncontrolled and may actually damage the part.  Forced-air systems are good, but they're cumbersome and expensive.  The circuit in Figure 1 uses a thermoelectric cooler (TEC) to provide closed-loop control of the element's temperature. __ Circuit Design by David Salerno, Unitrode Corp, Merrimack, NH

Controlling the temperature of fiber-optic lasers -  07/05/01  EDN Technical Article: Thermoelectric-cooler-based temperature controllers have some unusual requirements.  They account for circuit- and thermal-design characteristics to provide climatic pampering for temperamental lasers.   __ Circuit Design by Jim Williams, EDN's most revered contributor, passed away in June 2011 after a stroke.  He was 63.

Cooling Fan Controller -  As we begin to enjoy those lazy hazy days of summer, the most important thing on most of our minds is how to keep cool during those hot days.  For some of us that means turning up the old air conditioner and sipping on a nice cold glass of our favorite soft drink.  However, we often forget about an equally important __ Designed by Radio Amateur Society of Norwich

Digital Thermostat with LED Temperature Display -  I needed to replace two old, unreliable thermostats for controlling the heating and cooling for a large garden shed.  Commercial basic digital thermostats are available quite cheaply, but some lack the ability to control heavy loads or have the extra features that I require for saving energy when the door is often left open or to indicate temperature being out of range etc.  I like the PIC 18F1320 microcontroller used in my previous project, so decided to use it again in a very similar design to drive three multiplexed LED displays and read the temperature from a Dallas/DS18x20 "1-Wire" digital sensor.   __ Designed by D. Thorpe, 2006

Dual Comparator -  forms temperature-compensated proximity Detector __ Maxim Integrated

Electric Heater Thermostat -  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

Electronic Thermostat Relay -  Here is a simple thermostat circuit that can be used to control a relay and supply power to a small space heater through the relay contacts.  The relay contacts should be rated above the current requirements for the heater.  Temperature changes are detected by a (1.7KAT70F) thermistor placed in series with a 5K potentiometer which produces about __ Designed by Bill Bowden

Eliminate thermoelectric EMF in low-ohm measurements -  06/13/02 EDN Design Ideas:  When two different-metal conductors connect together in a loop and one of the junctions is at a higher temperature than the other, an electrical current flows through the loop.  The magnitude of this current depends on the type of metals involved and the temperature differential of the junctions.  When you open such a loop, a thermoelectric voltage appears across the open ends __ Circuit Design by John Wynne, Analog Devices, Limerick, Ireland

Fan control -  As we begin to enjoy those lazy hazy days of summer, the most important thing on most of our minds is how to keep cool during those hot days.  For some of us that means turning up the old air conditioner and sipping on a nice cold glass of our favorite soft drink.  However, we often forget about an equally important __ Designed by Radio Amateur Society of Norwich

Fan controller adapts to system temperature -  09/25/97 EDN Design Ideas:  Any piece of electronic equipment--whether it be a lab instrument, an audio amplifier, or a PC--that relies on a cooling fan to control internal temperature is a potential source of noise pollution or even hearing damage.  Most of the time, the fan's noise level is probably much higher than necessary, because it has enough capacity to move __ Circuit Design by Kerry Lacanette, National Semiconductor, Tucson, AZ

Fan Dual-Controller -  Each fan turns off when the temperature drops 5 degrees below its turn-on temperature.  For example, if the dial is set to 80 degrees, the fan turns on at 80 degrees and turns off at 75 degrees.  This prevents the fan from cycling on and off rapidly, which would occur if the fan turned on at 80, started to cool the cabinet, and then immediately turned off at 79.  __ 

Fan Speed Controller -  Simple circuit for fan speed control based on thermal feedback.  To reduce product noise.  Design idea   was rejected!  Years later companies are making millions from such circuits.   __ Designed by Jim Haggerman, Hagerman Technology LLC

Fan Thermostat -  Build a simple fan thermostat with LM35, ADC0804 and 89C51.   __ Designed by Wichit Sirichote

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 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 IC 1 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 supply - Still operating at 1.3V __ Contact Flavio Dellepiane, fladello @ tin.it

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

Got Designs?
Please eMail
if you want me to link to and/or post your original design.  Thanks.


Temperature Controls:  #'s - F       G - S       T - Z

 


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