Operational adjustment of the hysteresis in the thermostat. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Operational adjustment of the hysteresis in the thermostat. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Power regulators, thermometers, heat stabilizers

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The improvement of the thermometer-thermostat described in [1], which consisted in the introduction of an additional button for changing the set value of the maintained temperature downwards, and not just increasing, as was the case in the original version, was described in [2].

Over the period since this publication, the improvement of the instrument has continued. Another button was added that allows you to quickly, without reprogramming the microcontroller, change the hysteresis - the difference in the values of the temperature on and off the heater. This made it possible to easily adapt the device to different tasks and operating conditions. For example, an incubator requires a minimum and even zero width of the hysteresis zone, and for "warm floors" it can reach up to 2...4 °C. The optimal value is affected by the volume and thermal conductivity of the medium in which the temperature is maintained, the quality of its thermal insulation, the power of the heater, the distance between it and the temperature sensor, and other factors. Therefore, it is usually selected experimentally.

Rice. 1 (click to enlarge)

The scheme of the modified thermostat is shown in the figure. In addition to the previously available buttons SB1 and SB2 and the button SB3 with the resistor R16 added during the previous revision, the button SB4 and the resistor R17 are installed in it. The button assignments are now as follows:

SB1 - "+" (parameter increase);

SB2 - "Temperature";

SB3 - (parameter decrease);

SB4 - "Hysteresis".

Changed parameter values are stored in the EEPROM of the microcontroller and are transferred from it to the RAM each time the device is powered on.

Microcontrollers PIC16F84A or PIC16F628 can work in the device, but each according to its own program. For the PIC16F628 microcontroller, the ZQ1 quartz resonator and capacitors C1, C2 are not required. Its clocking will come from the built-in RC generator.

Programs for microcontrollers PIC16F84A and PIC16F628A of the modified thermometer-thermostat can be downloaded from ftp://ftp.radio.ru/pub/2012/06/hyst-term.zip.

Literature

Trishchenko K. Improved thermometer-thermostat on a microcontroller. - Radio, 2006, No. 1, p. 43-45.
Goethe A. Completion of the "Improved thermometer-thermostat on a microcontroller". - Radio, 2011, No. 11, p. 48.

Author: A. Goethe

See other articles Section Power regulators, thermometers, heat stabilizers.

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