Previously we have tried to do a single conversion of one ADC channel. We were waiting for the ADC result in a loop, which isn’t an effective way of using processor resources. It is better to trigger a conversion and wait for the conversion to complete the interrupt. This way, a processor can do other tasks rather than wait for ADC conversion to complete. This time we will go through another example to set up more than one channel and read ADC values using interrupt service routine.
- Possible circuit to connect a LED to an STM32. This solution leads to two different configurations schematized in figure 6: The first configuration is usually called Active High because LED is on when GPIO is set in High Logical State (i.e. Vcc, usually 3.3V on an official STM32 development board).
- A boardentry.txt file is generated to ease board declaration. Note that flash size used can be increased by 2k as now all pins are available in the PeripheralPins.c. To decrease it you can redefine the PinMap arrays at sketch level to only provide access to the used pins. See the Wiki custom pinmap array section. This release includes: Add.
- Two-dimensional Arrays. The simplest form of multidimensional array is the two-dimensional array. A two-dimensional array is, in essence, a list of one-dimensional arrays. To declare a two-dimensional integer array of size xy, you would write something as follows −. Type arrayName x y.
How would I declare a struct containing an array, or just an array or a struct for that matter, in Flash memory. I have read the variable placing example. But that only seems to work for simple variables. The following code just declares it in RAM.
How does multichannel ADC conversion works?
If we need to convert several channels continuously, we need to set up Sequence registers (ADC_SQRx). There are three sequence registers: ADC_SQR1, ADC_SQR2, and ADC_SQR3 where we can set up a maximum of 16 channels in any order. Conversion sequence starts with SQ1[4:0] settings in ADC_SQR3 register. Bits [4:0] hold the number of ADC channels.
All 16 sequence channels can be set up the same way through all SQR registers. Then in the ADC_SQR1 register, there are four bits marked L[3:0] where you can set the number how many times sequence reading will be repeated.
Another thing we will have to take care of is to set up sample time for each channel. As we know, each channel in sequence can be set for different conversion times. The sampling time for each channel can be set up in two registers: ADC_SMPR1 and ADC_AMPR2. There are three bits for each channel in sequence.
If you use a standard peripheral library setting up multichannel ADC becomes an easy task.
![Stm32 array declaration form Stm32 array declaration form](/uploads/1/0/7/2/107206099/929557187.png)
Setting up multichannel ADC conversion with DMA write
Let’s write an example where we will read the first 8 ADC channels four times using scan mode. Then we calculate an average value of each channel and later print results on a terminal screen using UART.
We will write ADC values to memory by using a DMA channel. Once all data is stored in memory, a DMA transfer complete interrupt will be generated to trigger averaging and output. In the STM32F100x datasheet, we find that ADC pins are assigned alternate functions as follows:
- ADC1_IN0 – PA0
- ADC1_IN1 – PA1
- ADC1_IN2 – PA2
- ADC1_IN3 – PA3
- ADC1_IN4 – PA4
- ADC1_IN5 – PA5
- ADC1_IN6 – PA6
- ADC1_IN7 – PA7
- ADC1_IN8 – PB0
- ADC1_IN9 – PB1
- ADC1_IN10 – PC0
- ADC1_IN11 – PC1
- ADC1_IN12 – PC2
- ADC1_IN13 – PC3
- ADC1_IN14 – PC4
- ADC1_IN15 – PC5
We will need to set up pins A0 to A7 as analog inputs for the first eight channels. Then we can set up an ADC conversion mode. Also, we need to set up Scan Conversion Mode to go through all channels selected in ADC1_SQRx registers. In the peripheral library, this looks like:
Then we must enable to enable continuous conversion mode as we want to cycle through channel list several times:
Then we indicate the number of channels to be converted in scan mode:
The next thing is to indicate which channels and what order we need to convert. For this, we set up each channel individually with commands:
I’ve chosen to go all eight channels in the row from 0 to 7. But you can mess up the numbers as you like. The rest is to set up DMA where it copies ADC values to memory on each EOC event. After DMA copies a predefined number of values, it generates an interrupt. Then we can manipulate data as we like. As in our example, we average multiple instances.
Stm32 Initialize Array
This is a result on the terminal screen.
Stm32 Array Declaration Codes
You can hook up a potentiometer or any other analog sensor to each channel to see its ADC value.
Working C code of multichannel ADC
Here is the complete main source code if you would like to analyze or use fragments for your purposes:
Stm32 Array Declaration Form
Also, you can download project files [STM32DiscoveryADC_DMAmultiple.zip] that compile with Codebench GCC and Eclipse.