need help with pyserial

[antichamber]

So, I'm running IDLE 3 on ubuntu mate on a raspberry pi and have an arduino uno connected via USB. Here is the code on the arduino:
int temp = 0;
void setup()
{
pinMode(ledPin, OUTPUT);
Serial.begin(9600);
Serial.setTimeout(10);
}
void loop()
{
while (Serial.available() > 0)
{
temp = Serial.parseInt();
if (temp == 0)
{
digitalWrite(13, HIGH);
delay(1000); \
digitalWrite(13, LOW);
delay(500);
}
}
if (temp > 0) {
temp--;
digitalWrite(13, HIGH);
delay(500);
digitalWrite(13, LOW);\
delay(500); } }

And is the first part of code on the raspberry pi:
import time
import serial
import struct
ser = serial.Serial('/dev/ttyACM0',9600)
data = 2
time.sleep(2)
print("sending now")

And now, the various attempts of sending stuff over serial, and their corresponding errors:
code: ser.write(data)
error: TypeError: 'int' object is not iterable

code: ser.write(str(data))
error: TypeError: an interger is required

code: ser.write(int(data))
error: TypeError 'int' object is not iterable

code: ser.write(struct('>B', data))
error: TypeError: 'module' object is not callable

Please tell me what I'm doing wrong or what I can do to make this work. I can't think of anything else to put in.

[mcgbb]

ser.write(str(data)) should work fine.

Only thing I can suggest is to step though the program line by line and check that when it gets to data=2 that the data variable has type 'int'

[Olav]

Perhaps you weren't aware but if you want people here to even look at your code it probably pays to put it in
tags and indent it properly. Your Arduino programme is nearly illegible the way you pasted it in here. Compare:
[code]
int temp = 0;

void setup() {

pinMode(ledPin, OUTPUT);
Serial.begin(9600);
Serial.setTimeout(10);

}

void loop() {

while (Serial.available() > 0) {

temp = Serial.parseInt();

if (temp == 0) {

digitalWrite(13, HIGH);
delay(1000);
digitalWrite(13, LOW);
delay(500);

}

}

if (temp > 0) {

temp--;
digitalWrite(13, HIGH);
delay(500);
digitalWrite(13, LOW);
delay(500);

}

}


Isn't that pretty.

Now for the Python part. You describe various errors:


code: ser.write(data)
error: TypeError: 'int' object is not iterable

code: ser.write(str(data))
error: TypeError: an interger is required

code: ser.write(int(data))
error: TypeError 'int' object is not iterable

code: ser.write(struct('>B', data))
error: TypeError: 'module' object is not callable

All these errors are telling you that serial.Serial.write() does not like the type of your 'data' variable and your conversions are not doing anything to fix the problem. So let's go back to the pySerial manual and see what the write() method actually expects as a parameter:

http://pyserial.readthedocs.io/en/latest/pyserial_api.html

It says, a bit down from the top of the page:


Write the bytes data to the port. This should be of type bytes (or compatible such as bytearray or memoryview). Unicode strings must be encoded (e.g. 'hello'.encode('utf-8').

Changed in version 2.5: Accepts instances of bytes and bytearray when available (Python 2.6 and newer) and str otherwise.

So in Python 3.x it wants a parameter of the Python built-in type bytes. You can read more about bytes here:

https://docs.python.org/3/library/stdtypes.html#binary-sequence-types-bytes-bytearray-memoryview

It looks then like you should be able to convert your variable with the method int.to_bytes() and then feed it into serial.Serial.write() like so:



data = 1
param = data.to_bytes(2, byteorder='little')
written = ser.write(param)


Or even:




ser.write((1).to_bytes(2, byteorder='little'))


We are converting to two bytes little endian because that is how the Arduino appears to like its integers.