Hello,
I am working with Raspberry pi3b which is connected to AD5686 via SPI communication. It is connected to the Chip select 1. I am trying to generate a sine wave using the DAC commanded by the raspberry pi in the frequency range of about 1000Hz to 10000Hz, But I am not getting exact sine wave. The quantization delay is too high such that for higher frequencies like 10000Hz I get only 4 or five steps for one sine wave. I have also tried with different clock frequencies up to 49Mhz. But there is no use. Only lower frequencies like 300 or 400Hz were able to be achieved Because the sampling frequency is so much higher than the sine repetition frequency. I will attach two samples of code which I have used. Please someone help me with this.
import spidev
import RPi.GPIO as GPIO
import time
import math
# Define GPIO pins
SYNC_PIN = 7
RESET_PIN = 22
POWER_PIN = 13
# Define SPI settings
spi = spidev.SpiDev()
spi.open(0, 1) # SPI bus 0, device 1
spi.mode = 0b10
spi.max_speed_hz = 40000000 # 1 MHz
# Setup GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(SYNC_PIN, GPIO.OUT)
GPIO.setup(RESET_PIN, GPIO.OUT)
GPIO.setup(POWER_PIN, GPIO.OUT)
def power_up():
GPIO.output(POWER_PIN, GPIO.HIGH)
def power_down():
GPIO.output(POWER_PIN, GPIO.LOW)
def reset():
GPIO.output(RESET_PIN, GPIO.LOW)
time.sleep(0.00004) # Minimum of 40 ns
GPIO.output(RESET_PIN, GPIO.HIGH)
def write_and_update_dac_channel(channel, data):
# Convert data to an integer
data = int(data)
# Construct the 24-bit command word for writing to and updating DAC channel
command_word = (0b0011 << 20) | (channel << 16) | data
# Send the command word over SPI
GPIO.output(SYNC_PIN, GPIO.LOW)
spi.xfer2([command_word >> 16, (command_word >> 8) & 0xFF, command_word & 0xFF])
GPIO.output(SYNC_PIN, GPIO.HIGH)
def generate_sine_wave():
SINE_DC_OFFSET = 32768
SINE_AMPLITUDE = 32767
SINE_WAVE_STEPS = 100
STEP_DELAY_MICROS = 8.13
sineWave = [0] * SINE_WAVE_STEPS
for i in range(SINE_WAVE_STEPS):
sineWave[i] = SINE_DC_OFFSET + SINE_AMPLITUDE * math.sin(i * 2 * math.pi / SINE_WAVE_STEPS)
i = 0
while True:
write_and_update_dac_channel(0b0001, sineWave[i])
i = (i + 1) % SINE_WAVE_STEPS
#time.sleep(STEP_DELAY_MICROS / 1000000) # Convert to seconds
def main():
power_up()
reset() # Reset the DAC initially
try:
generate_sine_wave()
except KeyboardInterrupt:
power_down()
GPIO.cleanup()
if __name__ == "__main__":
main()
import spidev
import RPi.GPIO as GPIO
import time
import math
# Define GPIO pins
SYNC_PIN = 7
RESET_PIN = 22
POWER_PIN = 13
# Define SPI settings
spi = spidev.SpiDev()
spi.open(0, 1) # SPI bus 0, device 1
spi.mode = 0b10
spi.max_speed_hz = 40000000 # 1 MHz
def setup():
GPIO.setmode(GPIO.BCM)
GPIO.setup(SYNC_PIN, GPIO.OUT)
GPIO.setup(RESET_PIN, GPIO.OUT)
GPIO.setup(POWER_PIN, GPIO.OUT)
def power_up():
GPIO.output(POWER_PIN, GPIO.HIGH)
def power_down():
GPIO.output(POWER_PIN, GPIO.LOW)
def reset():
GPIO.output(RESET_PIN, GPIO.LOW)
time.sleep(0.00004) # Minimum of 40 ns
GPIO.output(RESET_PIN, GPIO.HIGH)
def write_and_update_dac_channel(channel, data):
# Construct the 24-bit command word for writing to and updating DAC channel
command_word = (0b0011 << 20) | (channel << 16) | data
# Send the command word over SPI
GPIO.output(SYNC_PIN, GPIO.LOW)
spi.xfer2([command_word >> 16, (command_word >> 8) & 0xFF, command_word & 0xFF])
GPIO.output(SYNC_PIN, GPIO.HIGH)
def generate_sine_wave(min_value, max_value, frequency, phase_shift):
num_samples = 10000 # 50 seconds duration
for i in range(360):
# Calculate the sine wave value between 0 and 1
sine_value = (math.sin(2 * math.pi * i))
# Scale the sine value to the range between min_value and max_value
scaled_value = sine_value * (max_value - min_value)
# Shift the scaled value to the range between min_value and max_value
shifted_value = scaled_value + min_value
# Convert the sine value to 16-bit DAC input code
input_code = int(shifted_value)
# Write to and update DAC Channel A with the input code
write_and_update_dac_channel(0b0001, input_code)
time.sleep(0.001)
def main():
setup()
power_up()
reset() # Reset the DAC initially
try:
while True:
generate_sine_wave(min_value=32768, max_value=65535, frequency=1230, phase_shift=0)
except KeyboardInterrupt:
power_down()
GPIO.cleanup()
if __name__ == "__main__":
main()
