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Thermocouples are used to measure temperature
over a wide range. They are used in industry,
laboratories, transport, measuring and control
instrumentation, etc. It also happens that the
measurement should activate an alarm signal if the
temperature is not within the set range, which is an
additional advantage of this thermometer.
Specifications
• 1×6 LCD display
• temperature measuring range: 0...1024°C
400 °C to be measured)
• accuracy of measurement: ±1...2°C
• alarm for set measuring range
(included probe allows a maximum temperature of
• board size 35×116 mm
Circuit description
Thermometer with Thermocouple
and Alarm
Probe included with this unit can measure up to 400°C,
its cable length is 50 cm and the metal cap has an M6
thread. Typical measurement accuracy for
thermocouples is ±1...2°C, which exceeds the required
accuracy for most applications. Visualisation of the
result is realised on a 1x6 LCD display. In practice, for
this type of application, a display with such a small
number of characters is ideal. Communication of the
display with the microcontroller is in 4-bit mode. The
PR1 potentiometer is used to adjust the contrast of
the displayed characters, while the R2 resistor limits
the current flowing through the backlight diodes. For
alarm settings, the thermometer is equipped with
buttons S1 and S2. The alarm is set pressing either
button, with the upper button increasing the
temperature and the lower button decreasing it. Alarm
signal is a modulated sound generated by a buzzer.
Schematic diagram of the thermometer is shown in
Figure 1. Depending on the abilities and needs, the
circuit can be supplied with a DC voltage in the 8...15
V range. The voltage supplied to connector X1 via D1
diode is fed to stabiliser US1, which supplies +5 V.
The operation of the module is controlled by the
ATtiny2313 microcontroller, timed by an internal clock
signal, or more precisely by the program contained
therein. To ensure error-free temperature
measurement, a specialised IC module with integrated
cold-end compensation from Maxim-Dallas MAX6675
is used, which has an SPI interface through which it
communicates with the microcontroller. Due to the
module used, the construction of the thermometer is
extremely simple. The temperature measurement
module can measure temperature in the range
0...1024 °C. It is designed to work with a K-type
thermocouple sensor (chromel-alumel), which is most
commonly used in multimeters.
AVT 1960
ASSEMBLY DIFFICULTY
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