用Python获取基于火花塞驱动的内燃机状态

Question

致力于为定制越野车创建数据采集系统。使用Raspberry Pi和自定义转速表(测试并确认工作)来测量RPM。在下面的代码中使用中断来获取RPM值。

def get_rpm():                                         
    GPIO.wait_for_edge(17, GPIO.FALLING)
    start = time.time()
    GPIO.wait_for_edge(17, GPIO.FALLING)
    end = time.time()
    duration = end - start
    rpm = (1/duration)*60
    return rpm

此代码仅在引擎正在运行并产生火花时才起作用。如果没有火花，代码就会等待该边缘，不会继续执行。调用get_rpm()时，如果代码正在等待边缘，则会导致其他进程挂起。

我的解决方案是在另一个进程中获取引擎的状态。我认为它将在两个部分中工作得最好。

第1部分，在单独的线程中运行(循环)：

GPIO.wait_for_edge(17, GPIO.RISING)
last = time.time

第2部分，根据需要作为函数运行调用：

def get_state():
    while time.time - last < .5:
        engine_state = true
    else:
        engine_state = false
    return engine_state

随着第1部分将last保存到第2部分可访问的内存中，第2部分将根据火花塞最后一次触发的时间来确定汽车是否正在运行。使用engine_state作为比较器，只有当get_rpm()为真时，数据采集系统才会从engine_state获取并存储RPM值。

如何实现第1部分，以便可以在第2部分中使用last变量？last的变化将非常非常快。我不想在每次last更新时都将其存储到树莓派的SD卡上的文本文件中。我想在内存中存储last。

非常感谢！

Answer 1

这只是为了获得灵感。我手头没有我的Pis，所以这篇文章是盲目地根据记忆写的。

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)
GPIO.setup(17, GPIO.IN)
# the line below is important. It'll fire on both rising and falling edges
# and it's non-blocking
GPIO.add_event_detect(17, GPIO.BOTH, callback=callback_func)

length_of_last_high = 0
length_of_last_low = 0

last_rise = 0
last_fall = 0
last_callback = 0

def callback_func(pin):
    # all of these global variables aren't needed 
    # but I left them in for demo purposes
    global last_rise
    global last_fall
    global last_callback
    global length_of_last_high
    global length_of_last_low
    last_callback = time.time()
    if GPIO.input(17):
        print "Pin 17 is rising!"
        length_of_last_high = last_callback - last_rise
        last_rise = last_callback
    else:
        print "Pin 17 is falling!"
        length_of_last_low = last_callback - last_fall 
        last_fall = last_callback


# last passed as parameter (the preferred solution if it works).
# You test it - I can't at the moment
def get_state(last=last_rise):
    engine_state = False
    if time.time() - last < .5:
        engine_state = True
    return engine_state

# last as global variable. 
# This works too but global is bad practice if it can be avoided     
# (namespace littering)
def get_state2():
    global last_rise
    engine_state = False
    if time.time() - last_rise < .5:
        engine_state = True
    return engine_state


def main():
    while True:
        print "Not blocking! This loop could sleep forever. It wouldn't affect the readings"
        time.sleep(1)
        print get_state()

"""
GPIO.cleanup()
"""