STM32 ADC Multiple Channels
Today in this tutorial, we will see how to read multiple channels in ADC in STM32.
For this demonstration, I am using STM32F103C8 controller and True-Studio IDE.
For the ADC purpose, I am using 3 channels as mentioned below:-
- CHANNEL 0 –> IR sensor
- CHANNEL 1 –> Potentiometer
- CHANNEL 16 –> Internal Temp sensor
UPDATE
If the ADC Frequency is very high, the DMA Interrupt will execute at very high rate, and this will render the while loop Useless.
There is a different way to handle multiple channels without the DMA and you can check it at https://controllerstech.com/stm32-adc-multi-channel-without-dma/
HOW TO
In order to read the multiple channels, we need to use DMA. The benefit of it is the conversion will take place in the background and we can perform some other operation with the controller and when we need the values, we can just read them easily.
Before proceeding further, Let’s see How we have to get the value from the internal temperature sensor of the STM32. According to the reference manual (Pg- 236), The temp is given as follows
V25, Avg_Slope are given in the datasheet (Pg-79)
Also note that the ADC sampling time, while reading the temperature, needs to be maximum 17.1 us.
CubeMx Setup
- Above is the clock section from the CubeMx. Note that I have selected the ADC clock as 14 MHz.
- The reason behind this is that the Temp sensor sampling time needs to be 17.1 us.
- While in the ADC setting, we have maximum sampling time as 239.5 cycles. So (239.5/14) gives us 17.1 us sampling time.
Note that 3 channels are selected and the Continuous conversion mode is enabled. Also in the new CubeMx, you don’t need to worry about scan conversion mode. It will enable and disable by it’s own, based on if you are using multi channels or only one channel.
Above is the DMA setting for the ADC. Make sure that the DMA is circular and data width is selected as WORD or HALF WORD . This is because the CubeMx uses ADC in 12 bits resolution by default and in order to store 12 bits we need the variable of the same size.
Some Insight into the Code
uint32_t value[3];
HAL_ADC_Start_DMA(&hadc1, value, 3); // start adc in DMA mode- Starts the ADC in DMA mode and the converted data is stored in ‘value‘ buffer.
- ‘3’ is the length of data to be transferred from ADC peripheral to memory.
float temp;
#define V25 1.43 // from datasheet
#define VSENSE 3.3/4096 // VSENSE value
#define Avg_Slope .0043 // 4.3mV from datasheet
float get_temp (uint32_t variable)
{
return (((V25 - (variable*VSENSE)) / Avg_Slope) + 25); // formula from datasheet
}The above code gets the temperature of the sensor in °C. You can change the values of V25 and Avg_Slope according to your controller’s datasheet.
Result
