Parse data from sensor without delimeters

Question

Im using a variant of Arduino Due embedded on a ARM (Udoo). And I have connected a Medlab SPO2 Pearl 200 sensor to Serial1.

Im just trying to parse input from Serial1 to Serial, in a human-readable format (Hexadecimal).

The protocol is described in this image: Protocol SPo2

And using this Arduino code I reveice two times the "no finger detected line"

int lineLength = 16;
int spo2read[16];
int readed = 0;
 if (Serial1.available()) {
 int inByte = Serial1.read();
 if (readed < lineLength) {
 spo2read[readed] = inByte;
 }
 readed++;
 if (readed == lineLength) {
 Serial.print("SPO2: ");
 for (int i = 0; i <= lineLength; i++) {
 Serial.print(spo2read[i], HEX);
 Serial.print( delimeter);
 }
 Serial.println("");
 readed = 0;
 }
 }

Output with no finger is:

SPO2: A,FB,2,F9,0,FA,0,FC,A,FB,2,F9,0,FA,0,FC,0,

Buf if I put my finger, all is messed up:

SPO2: 7C,74,6B,62,5A,51,4A,42,3B,34,30,2E,2F,30,31,33,0,
SPO2: 36,38,3B,3E,3D,3C,3C,3B,3B,38,34,2F,2C,2B,2B,29,0,
SPO2: 24,21,1E,1D,1E,1E,1F,20,22,24,26,28,2B,2D,30,32,0,
SPO2: 35,37,39,3C,3E,40,42,44,45,4A,4F,53,55,57,59,5C,0,
SPO2: 5E,60,61,F9,0,FA,0,FC,1A,FB,0,F8,62,62,62,63,0,

Sensor doesn't sends a \n or \r so I don't know exactly how to parse the data

• geometrikal: It says there is a marker byte. You have to look for the marker byte to know when the message has ended.
• mpflaga: as per medlab-gmbh.de/english/downloads/pearl100_144.pdf page 13 marker bytes and example C code page 16 are values greater than or equal than F0

Answer 1

actually I don't think it is all mixed up

as per geometrikal use the markers to parse the data stream

I believe your above sample data started mid-stream during the 0xF8 of the wave form.

F8,...
...,7C,74,6B,62,5A,51,4A,42,3B,34,30,2E,2F,30,31,33,0,36,38,3B,3E,3D,3C,3C,3B,3B,38,34,2F,2C,2B,2B,29,0,24,21,1E,1D,1E,1E,1F,20,22,24,26,28,2B,2D,30,32,0,35,37,39,3C,3E,40,42,44,45,4A,4F,53,55,57,59,5C,0,5E,60,61
F9,0
FA,0
FC,1A
FB,0
F8,62,62,62,63,0,...

I believe reading this as a finite length does not portray the data for easy interpetation. Given that 0xF8 is a variable length protocol.

Where the reparse of your data initially appears to be legitimate parse.

That said I do read the SPO2, Pulse as zero. Where it may be likely the sensor has not finished its reading and auto gain cycles.

Answer 2

I have used the source code available on the Medlab web, and do some "modifications" to be Arduino compatible. I dont wanna the waveform data, because my final program will do the waveforms acording the data received, so I don't "listen" to the waveform packet

boolean startbyte = false; 
byte buf = 0;
 while (Serial1.available() > 3)
 {
 buf = Serial1.read();
 if (buf > 0xfc)
 {
 buf = Serial1.read();
 }
 if ((startbyte == true) && buf > 0xF7)
 {
 startbyte = false;
 }
 if (buf > 0xf7 && startbyte == false)
 {
 //startbyte = true;
 if (buf == 0xf8)
 {
 startbyte = true;
 }
 if (buf > 0xf8)
 {
 byte RX = buf;
 buf = Serial1.read();
 if (buf > 0xfc)
 {
 buf = Serial1.read();
 }
 if (RX == 0xf9)
 {
 //SPO = buf;
 Serial.print("SV:");
 Serial.print(buf, DEC);
 Serial.println();
 }
 else if (RX == 0xfa)
 {
 //Pulse = buf;
 Serial.print("SPV:");
 Serial.print(buf, DEC);
 Serial.println();
 }
 else if (RX == 0xfb)
 {
 //Status = buf;
 Serial.print("StV:");
 Serial.print(buf, DEC);
 Serial.println();
 }
 else if (RX == 0xfc)
 {
 //quality = buf;
 Serial.print("QV:");
 Serial.print(buf, DEC);
 Serial.println();
 Serial.println();
 }
 else { }
 }
 }
 else if (startbyte == true)
 {
 //Waveform data
 }
 }