Convert an array of hex values to 1 byte character to use in processing IDE

[MishalJasmine]

data_packet_header = [0x0A, 0xFA, 0x0C, 0x00, 0x02] is the array that I need to send to the processing IDE.

In processing IDE, the data is recieved in the following manner
inString = blePort.readChar();
pcProcessData(inString);

I have converted the data_packet_header into a array of 1byte using:
struct.pack('>B',data_packet_header[i]) resulting in [b'\n', b'\xfa', b'\x0c', b'\x00' , b'\x02']

But when printing the input data in Processing IDE, its not taking b'\n' as 1 char. instead its receiving b , ' ,\ , n , ' separately.

Can I get some help on this?

[jimmo]

I think you want bytes(data_packet_header)

[jimmo]

Please provide more context. How does the data get from you to processing? What do you do in MicroPython to send the data?

e.g. you must be doing something like:

payload = bytes(data_packet_header)
uart.write(payload)

[MishalJasmine]

RP2040 is connected to MAX3001 with which it communicates using SPI. The values are read back from MAX and plotted in processing IDE.

data_packet_header = [0x0A, 0xFA, 0x0C, 0x00, 0x02]

To send the data to the processing,

for i in range(0,len(data_packet_header)):
     print(data_packet_header[i])

if I use UART, it does not send data to processing.

[jimmo]

data_packet_header = [0x0A, 0xFA, 0x0C, 0x00, 0x02]

Yes but what comes after that?

[MishalJasmine]

After that there is an array of 12 elements which contains the ecg sample and the Bioz sample. After that a footer is sent which contains data_packet_footer = [0x00, 0x0B]

This is repeated every 8msec

[2dof]

@MishalJasmine I guess that " ..provide more context " from @jimmo question you meant (?): read ECG data from MAX via RP2040 and send them to the processing ide/computer by Bluetooth ( on IDE side read with your blePort class.) ? You send 'payload' like that ? : [

<ecg_daata>] at once or separately (from context i understand that all is send separately) ?

if You can please perform some "debug" info, like : print/ show payload (whole frame) before sending (on RPI side), on processing IDE side print/show inString.
"when I print the inString in processing ..() )" -> Yo mean pcProcessData() function or shortcut for 'processing ide' ?

[MishalJasmine]

The MAX30001 is connected to the RP2040 to collect the ECG data. The data collected is then sent to the processing for plotting. The format in which it is sent is as follows:

ecg_sample = ecg.to_bytes(4,'big') 
bioz_sample = bioz.to_bytes(4,'big')

Header:

data_packet_header = [0x0A, 0xFA, 0x0C, 0x00, 0x02]

data_packet[0] = ecg_sample[0]
data_packet[1] = ecg_sample[1]
data_packet[2] = ecg_sample[2]
data_packet[3] = ecg_sample[3]
data_packet[4] = bioz_sample[0]
data_packet[5] = bioz_sample[1]
data_packet[6] = bioz_sample[2]
data_packet[7] = bioz_sample[3]
data_packet[8] = 0xFF
data_packet[9] = 0x00
data_packet[10] = 0x00
data_packet[11] = 0x00

Footer:

data_packet_footer = [0x00, 0x0B]

The data is streamed to the processing in the following manner

for i in range(0,len(data_packet_header)):
       print(data_packet_header[i])
            
for i in range(0,len(data_packet)):
      print(data_packet[i])
        
for i in range(0,len(data_packet_footer)):
      print(data_packet_footer[i])

It appears to me the data is not getting streamed to the processing in the form of bytes.

[MishalJasmine]

I am facing the same issue as this link. Tried using bytes but the issue still exists.

[ricksorensen]

Python's print() function is largely for printing human readable representations of the arguments. Here is an example script which runs on both CPython and on micropython which tries to show what print generates and a possible 'raw' print solution. The expected raw result is 'AB' followed by a carriage return and new line.

import sys

d = [0x41, 0x42, 0x0D, 0x0A]  # 'AB\r\n'
db = bytes(d)
print("d:  int array, human readable")
print(d)
print("db: bytes array, human readable")
print(db)

print("db: bytes array, raw")
nw = sys.stdout.buffer.write(db)  # returns number written
print("| done {}\n\n".format(nw))

print("db: bytes array, raw, one at time")
# note on bytes
#   bytes(n)   ... n an integer, returns a null array of length n
#   bytes(str) ... str a string/iterable return an encoded array of len(str)
#  thus there is a need to convert the single/int byte value to an interable
for i in range(len(d)):
    _ = sys.stdout.buffer.write(bytes([d[i]]))  # or bytes(d[i:i+1]) or ..
print("| done {}\n\n".format(nw))

Here are the results on my CPython (Ubuntu 22.04) (Note- i made sure to flush the print(...flush=True) to keep order.

Python 3.10.6
d:  int array, human readable
[65, 66, 13, 10]
db: bytes array, human readable
b'AB\r\n'
db: bytes array, raw
AB
| done 4


db: bytes array, raw, one at time
AB
| done 4

This ran on my RP2040, ESP32C3, and Samd51 (WIO Terminal). My SAMD21 does not support sys.stdout.buffer Here is RP2040 result:

MicroPython v1.20.0-24-g867e4dd3d on 2023-04-27; XIAO RP2040 Local with RP2040
Type "help()" for more information.
>>>
Remount local directory ./ at /remote
>>> import chkbytesmp
d:  int array, human readable
[65, 66, 13, 10]
db: bytes array, human readable
b'AB\r\n'
db: bytes array, raw
AB
| done 4


db: bytes array, raw, one at time
AB
| done 4

`

[MishalJasmine]

yes.. I did observe that the \r\n gets appended to every byte that it streamed. If the number sent is 250, processing IDE is receiving it as b'250\r\n'. and it considers 2, 5, 0, /r and /n as a single byte.