DocID024134 Rev 2

13/17

AN4232

Application examples

16

The COMP_OutputBlanking example aims at showing how the blanking feature can be

used.

In this example, COMP1 is configured as follows:

•

The non-inverting input is connected to PA1

•

•

The output is available on PA0

•

The output is redirected to TIM1 BKIN to generate a break event when the non-

•

TIM1 OC5 is used as a blanking source

TIM1 is configured as follows:

•

TIM1 period is APB2 clock / period = 72000000/50000 = 1440 Hz

•

TIM1 CH2 (PA9) configured in PWM mode with a frequency equal to 1440 Hz and a

duty cycle pulse/period = 100 * (37500/50000) = 75%

•

TIM1 OC5 (internal channel: not available on GPIO) configured in PWM mode with a

frequency equal to 1440 Hz and a high level equal to pulse/period = 2000/72000000 =

27.7 microseconds

•

A break event is generated at a high polarity (when the non-inverting input is at a

higher voltage than the inverting input)

Note:

In STM32CubeF3 firmware package this example is available in the

Projects\STM32303C_EVAL\Examples\COMP\COMP_OutputBlanking and the

Projects\STM32303E_EVAL\Examples\COMP\COMP_OutputBlanking folders.

2.5

Humidity measurement

The analog comparators can be connected internally to input capture of embedded timers.

This feature makes it easy to measure the capacitance values using the charge/discharge

method. This “Humidity measurement” application is based on the HS1100/HS1101

capacitive relative humidity sensor available in the STM32303C-EVAL and STM32303E-

EVAL evaluation boards.

Note:

The application source code is available in the Project\STM32F30x_StdPeriph_Examples\

COMP\COMP_Hygrometer folder in the STM32F30x_DSP and standard peripherals library

package, stm32f30x_dsp_stdperiph_lib.

In STM32CubeF3 firmware package this example is available in the

Projects\STM32303C_EVAL\Examples\COMP\COMP_Hygrometer and the

Projects\STM32303E_EVAL\Examples\COMP\COMP_Hygrometer folders.

The capacitance measurement is performed using the variation of RxC time constant. A

square signal generated by TIM4 is passed through a charge resistance to

charge/discharge the capacitive sensor. The voltage on the sensor (Uc) is derived from the

equation below:

where:

–

R is the charge resistance

–

C is the capacitance of the sensor.