Thermal relay on a microcontroller with a digital sensor. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Thermal relay on a microcontroller with a digital temperature sensor. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Microcontrollers

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Thermal sensors are widely used in various areas of electronics. These are thermometers, fire alarm sensors, temperature monitoring of electronic equipment - amplifiers, power supplies, various converters, temperature protection of electronic devices, process control, etc. Both analog and digital sensors are used. The advantage of digital sensors is that the additional error of the measuring channel is eliminated, i.e. data from the sensor is taken already in a "ready" form, the ability to combine several sensors into a network for multi-zone measurement, which simplifies switching. Using the standard i2c bus as an interface greatly simplifies docking with other equipment.

In the described design of a simple thermal relay, an inexpensive digital temperature sensor of the Microchip company, type TCN75-5,0, is used. Small size, low cost and ease of use make the TCN75 ideal for integration into a variety of automation applications. The thermometer is designed to operate in the temperature range from -55 to +125 degrees, has a resolution of 0,5 degrees, measurement accuracy at a supply voltage of 5,0 volts 1 degree, which is ideal for these purposes. The thermal relay turns on the relay when the temperature drops below 19 degrees and turns it off when the temperature is above 23 degrees (room heater, it is possible to change the temperature of the relay operation).

The schematic diagram is shown in Fig. 1. The widely used PIC16F84A is used as a control microcontroller. LED indicator LED1 is designed to indicate the operation of the device. (blinks during operation) Relay P1 must be designed for a voltage of 12 volts and have contacts designed for switching loads. The node in the diagram of Fig. 1, designated as "1", can be temporarily installed to control the temperature and performance of the device after manufacture. The LCD will display the temperature in the middle from 0 degrees to +125 degrees. It is not required for further work.

Rice. 1 (click to enlarge)

To repeat this design, it is necessary to program the PIC16F84A microcontroller with firmware, which can be downloaded here.

Configuration bits: _XT_OSC _PWRTE_ON _CP_OFF _WDT_ON. Signet drawing in SprintLayout 4.0 format can be downloaded here.

Documentation (Datashit) for MK PIC16F84A

HEX firmware, as well as a drawing of the board, you can download here (17 kb).

Thermal relay on a microcontroller with a digital temperature sensor. Thermal relay printed circuit board
Fig. 2

For controller firmware, please contact the author.

The author accepts orders for the manufacture of devices for individual orders, and also sends programmed controllers complete with a printed circuit board to repeat published designs.

Author: Yakimenko Sergey, UT2HI; Publication: ut2hi.qrz.ru

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