john1998
Newbie level 6
I am trying to interface multiple PCF8591 (around 5) to a single Raspberry Pi using I2C protocol. Since a Rpi has only one set of SDA and SCL pins, I am trying to bit-bang to make the other GPIO pins work as SDA and SCL. I am trying to use RPi.GPIO library for making the bit banging code in python.
I don't understand how to communicate with PCF8591 even after referring to the manual plenty of times. I could not figure out how to receive data from a specific pin from PCF8591 since there are 4 pins available (AIN0, AIN1, AIN2, AIN3). I also want the input voltage as the differential voltage between two pins. It would be very helpful if anyone could tell me the steps to change and access different pins of PCF8591.
I am attaching the code I am using. I get a reading of '255' throughout whenever I run it. It is working more or less as I could see the SCA and SDA waveforms in an oscilloscope.
I don't understand how to communicate with PCF8591 even after referring to the manual plenty of times. I could not figure out how to receive data from a specific pin from PCF8591 since there are 4 pins available (AIN0, AIN1, AIN2, AIN3). I also want the input voltage as the differential voltage between two pins. It would be very helpful if anyone could tell me the steps to change and access different pins of PCF8591.
I am attaching the code I am using. I get a reading of '255' throughout whenever I run it. It is working more or less as I could see the SCA and SDA waveforms in an oscilloscope.
Code:
import RPi.GPIO as GPIO
import time
import matplotlib.pyplot as plt
pin_SCL = 0
pin_SDA = 0
signal = []
def plot_graph(time, data, graph_no, label_):
fig = plt.figure(graph_no)
axes = fig.add_subplot(111)
axes.patch.set_facecolor('black')
plt.plot(time, data, label = label_)
plt.ylabel('Voltage')
plt.xlabel('Time')
plt.legend(loc='upper right')
def set_pin(SCL, SDA):
global pin_SCL
global pin_SDA
pin_SCL = SCL
pin_SDA = SDA
GPIO.setup(pin_SCL, GPIO.OUT)
def start():
GPIO.setup(pin_SDA, GPIO.OUT)
GPIO.output(pin_SCL, GPIO.HIGH)
GPIO.output(pin_SDA, GPIO.HIGH)
time.sleep(10)
GPIO.output(pin_SDA, GPIO.LOW)
GPIO.output(pin_SCL, GPIO.LOW)
def send_byte(byte):
GPIO.setup(pin_SDA,GPIO.OUT)
for i in range(8):
GPIO.output(pin_SDA,byte & 0b10000000)
GPIO.output(pin_SCL,GPIO.HIGH)
GPIO.output(pin_SCL,GPIO.LOW)
byte = byte << 1
def acknowledge_from_slave():
GPIO.setup(pin_SDA,GPIO.IN)
GPIO.output(pin_SCL,GPIO.HIGH)
status = GPIO.input(pin_SDA)
GPIO.output(pin_SCL,GPIO.LOW)
if(status == GPIO.HIGH):
print("BYTE NOT RECEIVED")
def acknowledge_from_master():
GPIO.setup(pin_SDA,GPIO.OUT)
GPIO.output(pin_SCL,GPIO.HIGH)
GPIO.output(pin_SDA,GPIO.LOW)
GPIO.output(pin_SCL,GPIO.LOW)
def receive_byte():
global signal
byte = ''
GPIO.setup(pin_SDA,GPIO.IN)
for i in range(8):
GPIO.output(pin_SCL,GPIO.HIGH)
byte = byte + str(GPIO.input(pin_SDA))
GPIO.output(pin_SCL,GPIO.LOW)
byte = int(byte,2)
signal.append(byte)
if __name__ == "__main__":
global signal
GPIO.setmode(GPIO.BOARD)
set_pin(38,40)
start()
send_byte(0b10010001)
acknowledge_from_slave()
send_byte(0b00110000)#control byte to tell pcf8591 work as differential input
acknowledge_from_master()
try:
while True:
receive_byte()
acknowledge_from_master()
except KeyboardInterrupt:
plot_graph(range(len(signal)),signal,1,'Detected Signal')
plt.show()
GPIO.cleanup()
