Transfering float data between PC and Teensy

Projects Networking, Protocols, and Devices
1

I am trying to transfert float data between a PC (python) and a teensy 4.1.

Python code :

import numpy as np
import serial

data = np.array([1,0.5]).astype(np.float32) #this is test data, my real data is a lot bigger
S = serial.Serial(port='COM17',  baudrate=9600, timeout=1)
S.write(data.tobytes())
x=S.read(8)

Arduino code :

Serial.begin(9600);
while(!Serial.available());
byte buffer[8];
Serial.readBytes(buffer,8);
Serial.write(buffer,8);

The received bytes are different from the original bytes :

original : b'\x00\x00\x80?\x00\x00\x00?'
received : b'\x00\x80?\x00\x00\x00?c'

Leading to incorrect values, np.frombuffer(x,np.float32) : array([5.831554e-39, 3.523328e+21], dtype=float32)

2

Convert the float to a string before sending to arduino. Upon receiving it, use the atof() function to convert back to float.

3

transferring data in binary between systems can be difficult, e.g. different data lengths, endianness, number representation, etc

although transferring data in binary is more efficient and accurate it may be simpler initially to transfer the data as text, e.g. comma seperated floats such as 1.0,0.5,3.14159, 2.718281828, etc etc - once you have the system working look at binary again

also avoid uploading fragments of code it makes it difficult to understand and debug - upload complete programs (if the program is very large implement a simple test program which shows the problem)

also may be worth asking on the Python forum for help

4

ran the following python code on a Win10 PC
it transmits bytes of binary data and then displays text received

import numpy as np
import serial

data = np.array([1,0.5,3.14159, 2.718281828]).astype(np.float32) #this is test data, my real data is a lot bigger
print(data)
S = serial.Serial(port='COM6',  baudrate=115200, timeout=1)
S.write(data.tobytes())
print(data.tobytes())
#x=S.read(8)
print("reading serial");
while 1:
    try:
        # serial data received?  if so read byte and print it
        while S.in_waiting > 0:
            char = S.read()
            print(str(char,'ASCII'),end='')
    except:
        pass

ran following code on an ESP32
it receives 8 bytes of data, copies the bytes into float variables and displays the results
EDITED: to use a float array for results

void setup() {
  Serial.begin(115200);
  while (!Serial.available())
    ;
  byte buffer[100];
  int len = Serial.readBytes(buffer, 100);

  Serial.print(len);
   Serial.print(" bytes received "); for (int i = 0; i < len; i++) {
    Serial.print(" 0x");
    Serial.print(buffer[i], HEX);
  }
  Serial.println();
  Serial.print("sizeof(float) ");
  Serial.println(sizeof(float));
  // copy bytes into float variables and display
  float data[10];
  memcpy(data, buffer, len);
  Serial.print("data = ");
  for (int i = 0; i < len / sizeof(float); i++) {
    Serial.print(" ");
    Serial.print(data[i]);
  }
}

void loop() {}

python console displays

======================= RESTART: C:\Python311\SERIAL1.PY =======================
[1.        0.5       3.14159   2.7182817]
b'\x00\x00\x80?\x00\x00\x00?\xd0\x0fI@T\xf8-@'
reading serial
16 bytes received  0x0 0x0 0x80 0x3F 0x0 0x0 0x0 0x3F 0xD0 0xF 0x49 0x40 0x54 0xF8 0x2D 0x40

sizeof(float) 4

data =  1.00 0.50 3.14 2.72

binary data received OK and float values 1.0 and 0.5 are correct