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POpython serial reading issue after a period of inactivity
 

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  1. POpython serial reading issue after a period of inactivity
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    <p>I have an arduino board which keeps on dumping values to a serial port (USB) continuously. This data is read in by a machine using a python script using the pySerial library. The code I have used is as follows:</p> <pre><code>import serial import time ser = serial.Serial('/dev/ttyACM0', 9600, timeout=1) while True: ser.flushInput() #Clear the serial input buffer print "Value:" print ser.readline() print ser.readline() print ser.readline() time.sleep(30) #Wait for 30 seconds </code></pre> <p>This works perfectly and gives the following output:</p> <pre><code>Value: 162 162 162 Value: 162 162 162 </code></pre> <p>But when I give a much bigger delay than 30 seconds in the loop, say 1minute or higher:</p> <pre><code>time.sleep(60) #Wait for 60 seconds </code></pre> <p>I start getting issues. The 1st set of values are getting printed. From then on, the ser.readline() always times out yielding null values!</p> <p>Output:</p> <pre><code>Value: 162 162 162 Value: Value: </code></pre> <p>Why does the serial module show this behaviour? </p> <p>Initially the machine I used to read in the serial values was a Raspberry Pi board running a Raspian linux. I thought the issue might be due to the RPi putting off the USB to some low power sleep when it encountered an idle period. But I tested the same code on my laptop, then also the same issue was there, implying that it might be some other issue. </p> <p>I wanted to build a system which <strong>needs to be on 24x7</strong> and read in serial values upon certain event occurrences, so this behaviour is not acceptable.</p> <p>Please shed some light on this issue.</p>
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    1. USNabeel
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    1. COWhy do you need `time.sleep(30)` statement at the end?
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      1. POpython serial reading issue after a period of inactivity
      1. USAryaveer
    2. COThis is just a test code. The actual system I want should work something like this: 1. Wait for Event1 2. If Event1 occurs, get serial values till Event2 occurs 3. Keep repeating steps 1 and 2 The Event1 that I'm looking for doesn't occur very frequently. So after completing step2, it might take more than 1 minute for the next occurrence of Event1, after which the serial read gives me null values. The delay in the above test code is to model the time delay waiting for Event1. If it exceeds 1 minute, the system is not functioning as expected!
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      1. POpython serial reading issue after a period of inactivity
      1. USNabeel
    3. COI couldn't create your kind of setup ... unable to test. But you try `ser.inWaiting()` statement in loop and see what does it return in this case.
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      1. USAryaveer
 

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