Saving data

SPI is a protocol used to communicate with SD cards. The code in the SPI config listing initializes an SPI object with the correct parameters and uses the chip select pin (pin 1) to select the SD card. The initialization is done so that the microcontroller can write to and read from the SD card.

Listing configure SPI

cs = machine.Pin(1, machine.Pin.OUT)
spi = machine.SPI(0,
                  baudrate=1000000,
                  polarity=0,
                  phase=0,
                  bits=8,
                  firstbit=machine.SPI.MSB,
                  sck=machine.Pin(2),
                  mosi=machine.Pin(3),
                  miso=machine.Pin(4))
sd = sdcard.SDCard(spi, cs)
vfs = uos.VfsFat(sd)
uos.mount(vfs, "/sd")

The actual writing of the data to the SD card is done in this listing, here the file header is set first so that the correct variables can be assigned to the data later. The code uses a loop to vary the duty cycle of the device and measure the performance depending on it.

The duty cycle is increased incrementally from 0% to 70%. After each increase in duty cycle, the voltage, current, and power of the device are measured and written to a file. The file.flush() command ensures that the data is written to the file immediately and does not just remain in the buffer memory. The process continues indefinitely until the program is terminated.

Wirte data to SD listing

file = open('/sd/iu-data.txt', 'w')
file.write('duty' + ';' + 'voltage[0]' + ';' 
                        + 'current[0]' + ';' 
                        + 'power[0]' + '\n')
while(True):
    for duty in range(70):
        device.setDutyCycle(duty)
        time.sleep_ms(50)
        device.getfilteredADC()
        device.calcADCData()
        time.sleep_ms(50)
        file.write(str(duty) + ';' + 
                   str(device.voltage[0]) + ';' + 
                   str(device.current[0]) + ';' +
                   str(device.power[0]) + ';' +
                   '\n')
        file.flush()