Arduino Uno Raspberry Pi Serial Communication double readings

Question

I use an Arduino Uno to convert Analog data to digital from a light sensor and send this data to raspberry pi by an USB cable. However when I run the code I read values like 1923 from a 10-bit sensor.

Here is the arduino code

int a = A0;
int meas = 0;
void setup() {
Serial.begin(9600);
}
void loop() {
meas = analogRead(a);
if(Serial.readString() == "1"){ //Check that Raspberry wants data or not
Serial.println(meas);     
}
}

Here is the Python code in Raspberry Pi

import serial
from datetime import datetime
now = datetime.now()

ser = serial.Serial('/dev/ttyACM0', 9600)
ser.write("1".encode())
s = ser.readline()

file = open("dataset.txt", "a")
file.write(now.strftime("%Y-%m-%d %H:%M") + " Sensor Value:" + str(s)+ "\n")
file.close()

Here is the example output after running code once in every 5 minutes

14:08 Sensor Value:6
14:10 Sensor Value:8
14:15 Sensor Value:8
14:20 Sensor Value:10
14:25 Sensor Value:6
14:30 Sensor Value:9
14:35 Sensor Value:6
14:40 Sensor Value:7
14:45 Sensor Value:5
14:50 Sensor Value:5
14:55 Sensor Value:12
15:00 Sensor Value:1
15:05 Sensor Value:1
15:10 Sensor Value:10
15:15 Sensor Value:12
15:20 Sensor Value:14
15:25 Sensor Value:1922
15:30 Sensor Value:2211
15:35 Sensor Value:11
15:39 Sensor Value:6
15:40 Sensor Value:7
15:45 Sensor Value:8
15:50 Sensor Value:10
15:55 Sensor Value:1
16:00 Sensor Value:
16:05 Sensor Value:11

I want to get rid of these 1's and 1922 like things they are certainly meaningless data.

PS: Sensor is on the top of a mountain, I am using remote connection the check the data and manipulate the code.

How can I do that? Thank you for your time.

Try testing serial.available() before reading on the Arduino and waiting 200ms before the readline() on the Pi maybe. — Mark Setchell
– Mark Setchell, Commented Aug 27, 2018 at 15:56

frarugi87 · Accepted Answer · 2018-08-29 10:12:27Z

0

I think Mark Setchell is right. You are getting data from past measurements.

Personally I'd implement a more robust protocol, but since your application is quite basic you can try with a simpler approach, which is what he suggested.

This is solved easily by adding a small delay in the python program, between the request and the reading. Something like this can be enough:

from time import sleep
...
ser.write("1".encode())
sleep(0.05);
s = ser.readline()

In the mean time, I don't like the way you handle the reading in the arduino. If you are always sending single-char commands, I suggest this approach:

void loop() {
    meas = analogRead(a);
    if (Serial.available())
    {
        if (Serial.read() == '1')
        {
            Serial.println(meas);
        }
    }
}

This does not block the execution of the loop (which can come in handy if you plan to expand the functionalities)

answered Aug 29, 2018 at 10:12

frarugi87

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6 Comments

EkinEkinEkin Over a year ago

I tried what you said in my Python Code but now I am getting nothing from the arduino. In Raspberry Pi

frarugi87 Over a year ago

@EkinEkinEkin did you change the arduino code or just the python? which version of python are you running?

EkinEkinEkin Over a year ago

I change both and I am using python 2

frarugi87 Over a year ago

@EkinEkinEkin can you please share what you mean by "working sometimes, not working properly"? What are you receiving? What are you not receiving? What is the behavior you are experiencing and why it is not what you expect?

frarugi87 Over a year ago

@EkinEkinEkin ok, try to use the timeout option when opening the serial port (ser = serial.Serial('/dev/ttyACM0', 9600, timeout=1)). If it still does not work, try with a serial monitor to check if the communication with the arduino is ok and you are receiving what you expect

|

AYA · Accepted Answer · 2018-08-27 13:40:23Z

-1

You might have a look at calibration, here's a sample piece of code,

https://www.arduino.cc/en/Tutorial/Calibration

answered Aug 27, 2018 at 13:40

AYA

1,2179 silver badges8 bronze badges

5 Comments

EkinEkinEkin Over a year ago

But sensor is in a box on the top of a mountain

AYA Over a year ago

The code is for calibrating the values, emitted by the sensor. You need a method to limit the range of values.

EkinEkinEkin Over a year ago

I think it's caused by the asynchronous communication, have you any idea about to fix that?

gre_gor Over a year ago

No amount of miscalibration will make analogRead return more than 1023. Calibration won't fix it.

AYA Over a year ago

As you've mentioned miscalibration here, which implies a misunderstanding , calibration is not on the device but to determine and specify a valid range of values within the code. @EkinEkinEkin, have you tried posting on Sensors forums under arduino.cc. They would ask for the diagram and detailed sensor info as well.

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