当通过Python子进程获取数据时，在Raspberry Pi上LCD的每一行末尾有错误字符
问题描述 投票：2回答：2
我将兼容HD44780的LCD与Raspberry Pi B型相连。接线如下：
LCD Raspberry Pi Model B/B+
1 : GND 6 : GND
2 : 5V 2 : 5V
3 : Contrast (0-5V) 6 : GND
4 : RS (Register Select) 26 (GPIO7)
5 : R/W (Read Write) 6 : GND
6 : Enable 24 (GPIO8)
7 : Data Bit 0 --- NOT USED in 4 Bit mode ---
8 : Data Bit 1 --- NOT USED in 4 Bit mode ---
9 : Data Bit 2 --- NOT USED in 4 Bit mode ---
10: Data Bit 3 --- NOT USED in 4 Bit mode ---
11: Data Bit 4 22 (GPIO25)
12: Data Bit 5 18 (GPIO24)
13: Data Bit 6 16 (GPIO23)
14: Data Bit 7 12 (GPIO28)
15: LCD Backlight +5V** 2 : 5V
16: LCD Backlight GND 6 : GND
[当我执行此脚本时，该脚本只是通过Python子进程从系统中获取了一些主机信息，因此我在LCD的每一行末尾看到一个错误的字符。
#!/usr/bin/python
#
# HD44780 LCD Test Script for
# Raspberry Pi
#
# Author : Matt Hawkins
# Site : http://www.raspberrypi-spy.co.uk
#
# Date : 26/07/2012
#import
import RPi.GPIO as GPIO
import time
# Define GPIO to LCD mapping
LCD_RS = 7
LCD_E = 8
LCD_D4 = 25
LCD_D5 = 24
LCD_D6 = 23
LCD_D7 = 18
# Define some device constants
LCD_WIDTH = 16 # Maximum characters per line
LCD_CHR = True
LCD_CMD = False
LCD_LINE_1 = 0x80 # LCD RAM address for the 1st line
LCD_LINE_2 = 0xC0 # LCD RAM address for the 2nd line
# Timing constants
E_PULSE = 0.00005
E_DELAY = 0.00005
def main():
# Main program block
GPIO.setmode(GPIO.BCM) # Use BCM GPIO numbers
GPIO.setup(LCD_E, GPIO.OUT) # E
GPIO.setup(LCD_RS, GPIO.OUT) # RS
GPIO.setup(LCD_D4, GPIO.OUT) # DB4
GPIO.setup(LCD_D5, GPIO.OUT) # DB5
GPIO.setup(LCD_D6, GPIO.OUT) # DB6
GPIO.setup(LCD_D7, GPIO.OUT) # DB7
# Initialise display
lcd_init()
lcd_byte(LCD_LINE_1, LCD_CMD)
p = subprocess.Popen('''hostname''', stdout=subprocess.PIPE, shell=True)
hostname_output = p.communicate()[0]
lcd_string(hostname_output)
lcd_byte(LCD_LINE_2, LCD_CMD)
p = subprocess.Popen("ip addr | grep 'state UP' -A2 | tail -n1 | awk '{print $2}' | cut -f1 -d'/'", stdout=subprocess.PIPE, shell=True)
ip_address_output = p.communicate()[0]
lcd_string(str(ip_address_output))
def lcd_init():
# Initialise display
lcd_byte(0x33,LCD_CMD)
lcd_byte(0x32,LCD_CMD)
lcd_byte(0x28,LCD_CMD)
lcd_byte(0x0C,LCD_CMD)
lcd_byte(0x06,LCD_CMD)
lcd_byte(0x01,LCD_CMD)
def lcd_string(message):
# Send string to display
message = message.ljust(LCD_WIDTH," ")
for i in range(LCD_WIDTH):
lcd_byte(ord(message[i]),LCD_CHR)
def lcd_byte(bits, mode):
# Send byte to data pins
# bits = data
# mode = True for character
# False for command
GPIO.output(LCD_RS, mode) # RS
# High bits
GPIO.output(LCD_D4, False)
GPIO.output(LCD_D5, False)
GPIO.output(LCD_D6, False)
GPIO.output(LCD_D7, False)
if bits&0x10==0x10:
GPIO.output(LCD_D4, True)
if bits&0x20==0x20:
GPIO.output(LCD_D5, True)
if bits&0x40==0x40:
GPIO.output(LCD_D6, True)
if bits&0x80==0x80:
GPIO.output(LCD_D7, True)
# Toggle 'Enable' pin
time.sleep(E_DELAY)
GPIO.output(LCD_E, True)
time.sleep(E_PULSE)
GPIO.output(LCD_E, False)
time.sleep(E_DELAY)
# Low bits
GPIO.output(LCD_D4, False)
GPIO.output(LCD_D5, False)
GPIO.output(LCD_D6, False)
GPIO.output(LCD_D7, False)
if bits&0x01==0x01:
GPIO.output(LCD_D4, True)
if bits&0x02==0x02:
GPIO.output(LCD_D5, True)
if bits&0x04==0x04:
GPIO.output(LCD_D6, True)
if bits&0x08==0x08:
GPIO.output(LCD_D7, True)
# Toggle 'Enable' pin
time.sleep(E_DELAY)
GPIO.output(LCD_E, True)
time.sleep(E_PULSE)
GPIO.output(LCD_E, False)
time.sleep(E_DELAY)
if __name__ == '__main__':
try:
main()
except KeyboardInterrupt:
lcd_byte(LCD_LINE_1, LCD_CMD)
lcd_string("")
lcd_byte(LCD_LINE_2, LCD_CMD)
lcd_string("")
GPIO.cleanup()
此图像显示结果。
当我不使用子进程而只是插入任何字符串时，在每一行的末尾都不会出现错误的字符。这个例子证明了这一点：#!/usr/bin/python
#
# HD44780 LCD Test Script for
# Raspberry Pi
#
# Author : Matt Hawkins
# Site : http://www.raspberrypi-spy.co.uk
#
# Date : 26/07/2012
#import
import RPi.GPIO as GPIO
import time
import subprocess # Execute UNIX commands as subprocess
# Define GPIO to LCD mapping
LCD_RS = 7
LCD_E = 8
LCD_D4 = 25
LCD_D5 = 24
LCD_D6 = 23
LCD_D7 = 18
# Define some device constants
LCD_WIDTH = 16 # Maximum characters per line
LCD_CHR = True
LCD_CMD = False
LCD_LINE_1 = 0x80 # LCD RAM address for the 1st line
LCD_LINE_2 = 0xC0 # LCD RAM address for the 2nd line
# Timing constants
E_PULSE = 0.00005
E_DELAY = 0.00005
def main():
# Main program block
GPIO.setmode(GPIO.BCM) # Use BCM GPIO numbers
GPIO.setup(LCD_E, GPIO.OUT) # E
GPIO.setup(LCD_RS, GPIO.OUT) # RS
GPIO.setup(LCD_D4, GPIO.OUT) # DB4
GPIO.setup(LCD_D5, GPIO.OUT) # DB5
GPIO.setup(LCD_D6, GPIO.OUT) # DB6
GPIO.setup(LCD_D7, GPIO.OUT) # DB7
# Initialise display
lcd_init()
lcd_byte(LCD_LINE_1, LCD_CMD)
lcd_string("1st test line")
lcd_byte(LCD_LINE_2, LCD_CMD)
lcd_string('''2nd line here''')
def lcd_init():
# Initialise display
lcd_byte(0x33,LCD_CMD)
lcd_byte(0x32,LCD_CMD)
lcd_byte(0x28,LCD_CMD)
lcd_byte(0x0C,LCD_CMD)
lcd_byte(0x06,LCD_CMD)
lcd_byte(0x01,LCD_CMD)
def lcd_string(message):
# Send string to display
message = message.ljust(LCD_WIDTH," ")
for i in range(LCD_WIDTH):
lcd_byte(ord(message[i]),LCD_CHR)
def lcd_byte(bits, mode):
# Send byte to data pins
# bits = data
# mode = True for character
# False for command
GPIO.output(LCD_RS, mode) # RS
# High bits
GPIO.output(LCD_D4, False)
GPIO.output(LCD_D5, False)
GPIO.output(LCD_D6, False)
GPIO.output(LCD_D7, False)
if bits&0x10==0x10:
GPIO.output(LCD_D4, True)
if bits&0x20==0x20:
GPIO.output(LCD_D5, True)
if bits&0x40==0x40:
GPIO.output(LCD_D6, True)
if bits&0x80==0x80:
GPIO.output(LCD_D7, True)
# Toggle 'Enable' pin
time.sleep(E_DELAY)
GPIO.output(LCD_E, True)
time.sleep(E_PULSE)
GPIO.output(LCD_E, False)
time.sleep(E_DELAY)
# Low bits
GPIO.output(LCD_D4, False)
GPIO.output(LCD_D5, False)
GPIO.output(LCD_D6, False)
GPIO.output(LCD_D7, False)
if bits&0x01==0x01:
GPIO.output(LCD_D4, True)
if bits&0x02==0x02:
GPIO.output(LCD_D5, True)
if bits&0x04==0x04:
GPIO.output(LCD_D6, True)
if bits&0x08==0x08:
GPIO.output(LCD_D7, True)
# Toggle 'Enable' pin
time.sleep(E_DELAY)
GPIO.output(LCD_E, True)
time.sleep(E_PULSE)
GPIO.output(LCD_E, False)
time.sleep(E_DELAY)
if __name__ == '__main__':
try:
main()
except KeyboardInterrupt:
lcd_byte(LCD_LINE_1, LCD_CMD)
lcd_string("")
lcd_byte(LCD_LINE_2, LCD_CMD)
lcd_string("")
GPIO.cleanup()
此图像显示结果。没有错误的字符。
我使用的软件是Raspbian操作系统。
$ uname -a
Linux pi71 3.12.28+ #709 PREEMPT Mon Sep 8 15:28:00 BST 2014 armv6l GNU/Linux
$ python -V
Python 2.7.3
$ locate subprocess | grep 2.7
/usr/lib/pypy-upstream/lib-python/2.7/subprocess.py
/usr/lib/pypy-upstream/lib-python/2.7/test/subprocessdata
/usr/lib/pypy-upstream/lib-python/2.7/test/subprocessdata/sigchild_ignore.py
/usr/lib/pypy-upstream/lib-python/2.7/test/test_subprocess.py
/usr/lib/python2.7/subprocess.py
/usr/lib/python2.7/subprocess.pyc
我认为此问题是由子过程引起的。我该怎么做才能解决此问题？
感谢您的帮助！
我已将兼容HD44780的LCD与Raspberry Pi B型连接。接线如下：LCD Raspberry Pi B / B + 1型：GND ...
2个回答
投票
repr() function（或使用Python 3，repr()）检查字符串。这将产生字符串的字符串表示形式，可以将该字符串表示形式粘贴回您的解释器中，而不会造成麻烦，并且将显示任何不可打印或特殊的控制字符作为转义序列。投票
最新问题
- React-Select 更改时抛出“无法读取未定义的属性（读取“值”）”错误
- 如何在Spring Boot测试中从@ImportAutoConfiguration中排除classed
- 有没有办法点击iFunny网站首页的“登录”提示？
- 二维数组初始化的差异[重复]
- Expo SQLite 不相信“SQLiteDatabase”类型上存在“事务”
- 为什么数组中的输入会覆盖每行的值[重复]
- 如何修复Flutter中的注册错误？
- Python生成空嵌套列表和追加两种方式有什么区别？ [重复]
- Drools-engine 8.29.0.最终内存问题
- 带有 logo.img 和导航栏部分的标题
- SwiftUI .onAppear 不使用返回值更新 @State 变量
- 为什么用户 ID 部分有时不显示在 Firebase Crashlytics 仪表板中？
- 如何使 google-test 课程与我的课程成为朋友？
- MenuBarExtra 不更新
- 不是在 0,0 处替换，而是替换列表中 i 的零索引，为什么会这样呢？ [重复]
- .net（或其任何部分）是开源的吗？
- 在Python中编辑列表列表的列表[重复]
- 如何基于特定字段合并 2 个对象列表，且与值无关
- 字符串反转未发生
- 为什么 TypeScript 让我使用界面上未定义的键？