通过Raspberry Pi 3B上的串行端口访问传感器

Question

I've got the following problem and after long hours of frustration I cannot get it to work, could somebody please help a noob out?

I've several SRF02 Ranging sensors which I wanted to use through I2C on my Raspberry Pi 3B Jessie.

I followed the tutorial and changed the first sensor to address 0xF2 (0x79 seen from Raspberry) and it all went perfectly. But the problem is that the addresses 0x78 to 0x7B are reserved for 10-bit I2C Adressing, so I have to use another one. But since I cannot access it anymore through I2C since I changed the address I decided to do it through the serial port.

I tried changing it as described in the tutorial but it doesn't work. Here is the code and what I did after research to get it done:

• I checked the address of the Sensor. On powering up it sends one long and 9 short flashes so its address should be 0x09 in serial mode.

• I updated and upgraded my Raspberry.

• I connected the sensors RX pin to the Rasp TX and viceversa. +5V of the sensor to +3V of the Rasp (Is this a problem?). Sensors ground and mode pin to ground.

• On raspi-config I changed the serial console to disabled and the serial harware ports to enabled.

Here is my /boot/cmdline.txt:

dwc_otg.lpm_enable=0 console=tty1 root=/dev/mmcblk0p7 rootfstype=ext4 elevator=deadline fsck.repair=yes rootwait quiet splash plymouth.ignore-serial-consoles

I added the following to my /boot/config.txt:

enable_uart=1
dtoverlay=pi3-disable-bt
core_freq=250

My python code (By sending the range commands the sensor should flash once, but it doesn't, also I don't get any Result):

import serial
import time

ser = serial.Serial(port='/dev/serial0', baudrate = 9600, bytesize=serial.EIGHTBITS, parity=serial.PARITY_NONE, stopbits=serial.STOPBITS_TWO, timeout=1, write_timeout=5)

USED_ADDRESS = '0x09'
TARGET_ADDRESS = '0x03'

# GET DISTANCE IN CM

ser.write(USED_ADDRESS)
ser.write('0x51')

time.sleep(0.07)

ser.write(USED_ADDRESS)
ser.write('0x5E')

results = ser.read(2)

if(results != None and len(results) > 0):
        print 'RESULTS:'
        for result in results:
                print result
else:
        print 'NO RESULT'

#CHANGING ADDRESS

#First command

ser.write(USED_ADDRESS)
ser.write('0xA0')

#Second command

ser.write(USED_ADDRESS)
ser.write('0xAA')

#Third command

ser.write(USED_ADDRESS)
ser.write('0xA5')

#Target Address

ser.write(USED_ADDRESS)
ser.write(TARGET_ADDRESS)

print "DONE"

Result of dmesg | grep tty:

[    0.000000] Kernel command line: 8250.nr_uarts=1 bcm2708_fb.fbwidth=640 bcm2708_fb.fbheight=480 bcm2708_fb.fbswap=1 vc_mem.mem_base=0x3dc00000 vc_mem.mem_size=0x3f000000  dwc_otg.lpm_enable=0 console=tty1 root=/dev/mmcblk0p7 rootfstype=ext4 elevator=deadline fsck.repair=yes rootwait quiet splash plymouth.ignore-serial-consoles
[    0.000312] console [tty1] enabled
[    0.748748] 3f201000.serial: ttyAMA0 at MMIO 0x3f201000 (irq = 87, base_baud = 0) is a PL011 rev2

Result of ls -l /dev/serial*:

lrwxrwxrwx 1 root root 7 Feb 16 15:06 /dev/serial0 -> ttyAMA0
lrwxrwxrwx 1 root root 5 Feb 16 15:06 /dev/serial1 -> ttyS0

Somebody got an idea? I would be super-duper gratefull for any hint.

Answer 1

Ok guys I solved it! I found the solution here: https://www.raspberrypi.org/forums/viewtopic.php?t=63419

Connections as follows:

Pi 5V to device 5V Pi ground to device ground Pi ground to device mode Pi TX to device RX

Then configure the Pi serial link to 9600.

stty -F /dev/ttyAMA0 9600

Then use echo to send commands to the device.

The first byte is the device address (0 - 15). The second byte is a command.

To change the device from address 0 to address 5 use

echo -ne "\\x00\\xA0\\x00\\xAA\\x00\\xA5\\x00\\x05" >/dev/ttyAMA0

To change the device from address 5 back to address 0 use

echo -ne "\\x05\\xA0\\x05\\xAA\\x05\\xA5\\x05\\x00" >/dev/ttyAMA0

All the details are in the docs you linked.