CM3-Home technical documentation Buy
Serial port interface
A serial port interface at 3.3 volt is available on the CM3-Home to connect external microcontrollers like Arduino or ESP8266.
The signals are available on screw terminals as visible below and are at 3.3 volt level. The lines are not-tolerant to 5 volt.
How to use the serial port
This port is visible in Linux as /dev/ttyUSB3 device.
Example in Python
Install the Python serial library:
sudo apt-get update
sudo apt-get install python-serial
This example sends a string on the serial port each 1 second at 115200,N,8,1 and checks if any character is received from a remote serial terminal.
#!/usr/bin/python
import serial
import time
ser = serial.Serial(
port='/dev/ttyUSB3',
baudrate=115200,
timeout=1,
parity=serial.PARITY_NONE,
stopbits=serial.STOPBITS_ONE,
bytesize=serial.EIGHTBITS
)
ser.flushOutput()
ser.flushInput()
rx_counter=0
tx_counter=0
while True:
tx_counter=tx_counter+1
ser.write("Tx counter = %d | Rx counter = %d\n\r" % (tx_counter,rx_counter))
print("Tx counter = %d | Rx counter = %d" % (tx_counter,rx_counter))
a=ser.read(1)
if a:
rx_counter=rx_counter+1
ser.write("Tx counter = %d | Rx counter = %d | Received: %s %02x\n\r" % (tx_counter,rx_counter,a,ord(a)))
print("Tx counter = %d | Rx counter = %d | Received: %s %02x" % (tx_counter,rx_counter,a,ord(a)))
Listing ports
The command:
python -m serial.tools.list_ports
will print a list of available serial ports.
Note
This serial port is slightly different from the Raspberry PI3 /dev/ttyAMA0. Some programs initialize pyserial in this way
def connect(self):
""" Connects to the device and starts the read thread """
self.serial = serial.Serial(dsrdtr=True, rtscts=True, port=self.port, baudrate=self.baudr$
timeout=self.timeout,*self.com_args,**self.com_kwargs)
This doesn't work correctly on the /dev/ttyUSB3, the hardware handshake criteria must be disabled, as is in the default configuration, they are not managed:
def connect(self):
""" Connects to the device and starts the read thread """
self.serial = serial.Serial(dsrdtr=False, rtscts=False, port=self.port, baudrate=self.baudr$
timeout=self.timeout,*self.com_args,**self.com_kwargs)
