Application description

AN3260

6/24

Doc ID 17836 Rev 1

3.2

Application schematics

and the pushbuttons with the STM8S-DISCOVERY.

Button1 and button2 require an RC debounce filter to avoid triggering several interrupts. The

debounce filter for button1 and button2 consist of C7 and C6 capacitors plus PA3 and PA4

internal pull-up resistor (about 45 KΩ).

No external pull-up resistors are required as the internal pull-ups of the I/Os are used.

C2 and C3 are two charge-pump external capacitors which are used in the ST232C as

voltage doubler and voltage inverter, respectively.

The current flowing into the LM235 V+ pin must be regulated by a resistor. The sensor is

directly proportional to the absolute temperature with a sensitivity of 10mV/°K. Since the

ambient temperature is around 300 °K, the voltage drop is roughly 3 V, which leaves 2 V for

the 2.2 kΩ resistor to regulate the current around 1 mA (intensity used to determine the

typical values in the datasheet).

For implementation details, refer to the STM8S-DISCOVERY board schematics provided in

the STM8S-DISCOVERY user manual (UM0817).

Table 2.

List of packaged components

Part number

Component description

Package

ST232C (order

code

ST232CN)

Very-high speed ultralow-power consumption 5 V RS232

driver/receiver used for UART 5/12 V level shifter.

SO16

LM235

Precision temperature sensor IC operating over a -40 to -125 °C

temperature range with 1 °C initial accuracy.

SO8