AN3397

Temperature sensor application description

Doc ID 018809 Rev 1

11/24

2.4

Temperature sensor application principle

The STM8L152C6 has a built-in temperature sensor (TS) which is internally connected to

the analog-to-digital converter (ADC) TS input channel. The ADC converts the sensor

output voltage into a digital value. The result is recalculated into standard temperature units

(°C in this example) and displayed on the LCD.

The temperature value displayed on the LCD panel is refreshed after every 1 s time period.

To improve measurement reliability, this data point is obtained by averaging 20

measurements. Between each temperature measurement, the STM8L152C6 enters active

halt mode to minimize average power consumption, then automatically wakes up 50 ms later

to get a new data point and process it.

The TS application may also display the minimum and maximum temperature values

recorded since the STM8L-DISCOVERY was powered up. By default, the current

temperature is displayed with the symbol 'T'. When the user push-button is pressed once,

the LCD displays the maximum temperature recorded with the symbol 'M'. The second time

the user push-button is pressed, the minimum temperature recorded is displayed with the

symbol 'm'. Pressing the user push-button again displays the current temperature once

more (see Figure 4).

Figure 4.

TS application user interface

The TS can also be used to detect temperature variations. Using the LCD bar graph, the

application displays the temperature trend over the past five-minute period. If the

temperature values recorded during that time have dropped, BAR0 is turned ‘on’. On the

other hand, if the temperatures have increased, BAR3 is turned on.

LCD

T +24.7 °C

Current temperature

Max temperature recorded

Min temperature recorded

USER push-button

Temperature drop

ai18761

Temperature rise

M +26.4 °C

m+21.6 °C