STM32F4 DAC not working

[Rect Cream]

Posted on January 28, 2017 at 23:40

hi,

   I am trying to use discovery board DAC module to adjust my external led's brightness by giving different level out voltage.

   I am sure that led is working on 3V, GPIOA.PA5 port also is working.

   But when I run the following my DAC module, the led has no light at all. Any ideas?

  void main()

  {    uint32_t Ret;    HAL_Init();    __HAL_RCC_GPIOA_CLK_ENABLE();    GPIO_InitTypeDef GPIOInitDef;    GPIOInitDef.Pin = GPIO_PIN_4;    GPIOInitDef.Mode = GPIO_MODE_ANALOG;    GPIOInitDef.Pull = GPIO_NOPULL;    GPIOInitDef.Speed = GPIO_SPEED_FREQ_LOW;    HAL_GPIO_Init(GPIOA, &GPIOInitDef);

    DAC_HandleTypeDef DACHandleTypeStruct;

    DACHandleTypeStruct.Instance = DAC;    Ret = HAL_DAC_Init(&DACHandleTypeStruct);

    DAC_ChannelConfTypeDef DACChannelConfStruct;

    DACChannelConfStruct.DAC_Trigger = DAC_TRIGGER_NONE;    DACChannelConfStruct.DAC_OutputBuffer = DAC_OUTPUTBUFFER_ENABLE;    Ret = HAL_DAC_ConfigChannel(&DACHandleTypeStruct,&DACChannelConfStruct, DAC_CHANNEL_1);    Ret = HAL_DAC_Start(&DACHandleTypeStruct, DAC_CHANNEL_1);    HAL_DAC_SetValue(&DACHandleTypeStruct, DAC_CHANNEL_1, DAC_ALIGN_12B_R, 0x0FFF);

    while(1)

    {      ;    }

}

#dac

[Tesla DeLorean · Accepted solution]

Posted on January 29, 2017 at 01:24

>>Any ideas? 

An inability to source sufficient current? Try using a TIM pin in PP mode using PWM

[S.Ma]

Posted on January 29, 2017 at 08:45

Agree with Clive One, PWM has current strength while buffered DAC is intended for analog circuitry driving (and not direct LED). 

[AvaTar]

Posted on January 30, 2017 at 07:52

A look at the datasheet would have revealed that the DAC output impedance is about 2 orders (buffered mode) or 5 orders of magnitude(unbuffered mode) too high.

And for dimming, analogue output is less suitable. As suggested, dimming / PWM is more energy efficient.