Jonas Skalman
Reading SenseAir LP8 CO2 sensor over bluetooth low energy
Dependencies: BLE_API mbed nRF51822
Diff: LP8.h
- Revision:
- 0:ee3787c8e209
- Child:
- 1:b512a405b584
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/LP8.h Fri Apr 21 13:26:06 2017 +0000
@@ -0,0 +1,284 @@
+#ifndef LP8_H
+#define LP8_H
+
+class LP8
+{
+public:
+
+ //constructor
+ LP8(Serial &device, DigitalOut &vbb, DigitalOut &vbb_en, DigitalIn &rdy, Timer &_timer): /* initiate class object */
+ Device(device),
+ VBB(vbb),
+ VBB_EN(vbb_en),
+ RDY(rdy),
+ lp8Wait(_timer)
+ {
+ Device.baud(9600); //set baud rate to 9600
+
+ //initialize arrays with modbus commands.
+ //initial startup command
+ firstWrite[0] = 0xfe;
+ firstWrite[1] = 0x41;
+ firstWrite[2] = 0x00;
+ firstWrite[3] = 0x80;
+ firstWrite[4] = 0x01;
+ firstWrite[5] = 0x10;
+ firstWrite[6] = 0x28;
+ firstWrite[7] = 0x7e;
+
+ //write sensor state to lp8 command
+ stateWrite[0] = 0xfe; //device adress
+ stateWrite[1] = 0x41; //read/write
+ stateWrite[2] = 0x00; //
+ stateWrite[3] = 0x80; //starting adress
+ stateWrite[4] = 0x18; //nr of bytes to send
+ stateWrite[5] = 0x20; //Calculation Control
+ for(int k = 6; k < 31; k++) { stateWrite[k] = 0x00; }
+
+ //read lp8 state command
+ stateRead[0] = 0xfe;
+ stateRead[1] = 0x44;
+ stateRead[2] = 0x00;
+ stateRead[3] = 0x80;
+ stateRead[4] = 0x2c;
+ stateRead[5] = 0x00;
+ stateRead[5] = 0x00;
+ //response buffer
+ for(int k = 0; k < 60; k++) { response[k] = 0x00; }
+
+
+// gC = 0x00;
+ co2 = 400;
+ counter = 0;
+ CRC = 0x0000;
+ _timeMe = 0.3;
+ };
+
+
+ //send startup msg .
+ bool lp8Init(){
+ VBB.write( 1 );
+ VBB_EN.write( 1 ); //power on
+ timeIt( _timeMe );
+
+ transmitPacket(firstWrite, 8); //Send out msg (and nr of elements) over serial line
+ Response( 4 ); //read 4 bytes response
+
+ if( RDY.read() == 0 ) {
+ lp8Wait.start();
+ while( lp8Wait.read() < 0.5 ) { /* spin */ }
+ lp8Wait.stop();
+ lp8Wait.reset();
+ }
+
+//compute crc
+ CRC = modbusCrc(stateRead, 5);
+//add crc value to the transmit package
+ stateRead[5] = (uint8_t)CRC; //crc_H
+ stateRead[6] = (uint8_t)(CRC >> 8); //crc_L
+ timeIt( _timeMe ); //wait for message to be sent and processed
+ transmitPacket(stateRead, 7); //transmit packet
+ Response( 49 ); //read sensor state and co2 value(s)
+
+ VBB_EN.write( 0 ); //power off
+ VBB.write( 0 );
+
+//was the talk a success?
+ if ( getValue() < 1 ) {
+ return 1; }
+ else {
+ return 0; }
+
+ };
+
+
+ //send subsequent messages to the lp8
+ void lp8Talk(){
+
+ //transfer previous sensor state to the new msg out
+ for (int u = 4; u < 23+4; u++) {
+ stateWrite[u+2] = response[u];
+ }
+ //compute new crc value
+ CRC = modbusCrc(stateWrite, 29);
+ //add new crc value to send list
+ stateWrite[29] = (uint8_t)CRC;
+ stateWrite[30] = (uint8_t)(CRC >> 8);
+
+
+ //initialize new transfer sequence
+ VBB.write( 1 );
+ VBB_EN.write( 1 ); //power on sensor
+ timeIt( _timeMe );
+
+ transmitPacket(stateWrite, 31); //Send out msg with previous state (and nr of elements) over serial line
+ Response( 4 ); //read 4 bytes response
+
+ //compute crc
+ CRC = modbusCrc(stateRead, 5);
+ //add crc value to the read request transmit package
+ stateRead[5] = (uint8_t)CRC; //crc_l
+ stateRead[6] = (uint8_t)(CRC >> 8); //crc_h
+ //send read request
+ transmitPacket(stateRead, 7); //transmit packet
+ //read sensor response
+ Response( 49 ); //read sensor state and co2 value(s)
+
+ VBB_EN.write( 0 ); //power off
+ VBB.write( 0 );
+ };
+
+
+
+ //get co2 value from lp8 response
+ unsigned long getValue()
+ {
+ int high = response[29];
+ int low = response[30];
+ unsigned long val = high * 256 + low;
+
+ return val;
+ }
+
+
+
+ /************************************************* Helper Functions ********************************************/
+ /************************************************* ********************************************/
+ void responsePurge(int bytesToPurge){
+ for (int j = 0; j < bytesToPurge; j++) {
+ response[j] = 0x00;
+ }
+ };
+
+
+ //read from the lp8
+ void Response(int bytesToRead ){
+ lp8Wait.start(); //poll rx line for x seconds
+ do {
+ if(Device.readable()) {
+ response[counter] = Device.getc();
+ counter++;
+ }
+ }
+ while( lp8Wait.read() < 0.5 );
+ counter = 0;
+ lp8Wait.stop();
+ lp8Wait.reset();
+ };
+
+ void transmitPacket(uint8_t msg[], int le ){
+ //Send out msg over serial line:
+ while(!Device.writeable() ) { /* wait for serial available*/ }
+ for(int pos = 0; pos < le; pos++) {
+ Device.putc(msg[pos]);
+ }
+
+ };
+
+ //timer
+ void timeIt(float &timeMe){
+ //start amd stop timer...
+ lp8Wait.start();
+ while (lp8Wait.read() < timeMe ) { /* W A I T I N G */ }
+ lp8Wait.stop();
+ lp8Wait.reset();
+ };
+
+ // Computation for the modbus 16-bit crc
+ uint16_t modbusCrc(uint8_t buffer[], int len){
+ uint16_t crc = 0xFFFF;
+
+ for (int pos = 0; pos < len; pos++) {
+ crc ^= (uint16_t)buffer[pos]; // XOR byte into least sig. byte of crc
+
+ for (int i = 8; i != 0; i--) { // Loop over each bit
+ if ((crc & 0x0001) != 0) { // If the LSB is set
+ crc >>= 1; // shift right and XOR 0xA001
+ crc ^= 0xA001;
+ }
+ else // Else LSB is not set
+ crc >>= 1; // shift right
+ }
+ }
+ // Note, this number has low and high bytes swapped
+ return crc;
+ };
+
+
+
+
+private:
+
+ Serial &Device;
+ DigitalOut &VBB;
+ DigitalOut &VBB_EN;
+ DigitalIn &RDY;
+ Timer &lp8Wait;
+
+ //msg containers (needs to be initialized at constructor level)
+ uint8_t firstWrite[8];
+ uint8_t stateWrite[31];
+ uint8_t stateRead[7];
+ uint8_t response[60];
+
+ int co2; //CO2 initial value
+ int counter; //simple counter
+ uint16_t CRC; //modbus crc value
+ float _timeMe; //timer value
+// uint8_t gC; //getCharacter...
+
+
+};
+#endif
+
+/*
+LP8 Communication Protocol (With no external Pressure Sensor):
+--------------------------------------------------------------------------------
+Initial Measurement (first read after powerup): COMMANDS:
+--------------------------------------------------------------------------------
+1) host powers up sensor: VBB_EN = 1
+2) host waits until rdy signal goes low: RDY = 0;
+3) host writes command, "write 24 bytes starting from adress 0x0080": { 0xfe, 0x41, 0x00, 0x80, 0x18, 0x10, ... [any 23 bytes] ..., CRC_low, CRC_high };
+4) host reads response: { 0xfe, 0x41, 0x81, 0xe0 };
+5) host waits until rdy signal goes high: RDY = 1;
+6) host writes command "read 44 bytes starting from adress 0x0080": { 0xfe, 0x44, 0x00, 0x80, 0x2c, CRC_low, CRC_high };
+7) host reads response: { 0xfe, 0x44, 0x2c, 0x00, SS1, SS2, ..., SS23, PP_H, PP_L, D1, D2, ..., D18, CRC_low, CRC_high };
+8) host powers down sensor: VBB_EN = 0;
+
+[------------------------------------------------------------------------------]
+Optional first reading W/O pressure sensor
+[------------------------------------------------------------------------------]
+1) host powers up sensor: VBB_EN = 1
+2) host waits until rdy signal goes low: RDY = 0;
+3) host writes command, "write 24 bytes starting from adress 0x0080": { 0xfe, 0x41, 0x00, 0x80, 0x18, 0x10, 0x28, 0x7e };
+4) host reads response: { 0xfe, 0x41, 0x81, 0xe0 };
+5) host waits until rdy signal goes high: RDY = 1;
+6) host writes command "read 44 bytes starting from adress 0x0080": { 0xfe, 0x44, 0x00, 0x80, 0x2c, CRC_low, CRC_high };
+7) host reads response: { 0xfe, 0x44, 0x2c, 0x00, SS1, SS2, ..., SS23, PP_H, PP_L, D1, D2, ..., D18, CRC_low, CRC_high };
+8) host powers down sensor: VBB_EN = 0;
+
+
+--------------------------------------------------------------------------------
+Subsequent readings:
+--------------------------------------------------------------------------------
+1) host powers up sensor: VBB_EN = 1
+2) host waits until rdy signal goes low: RDY = 0;
+3) host writes command, "write 24 bytes starting from adress 0x0080": { 0xfe, 0x41, 0x00, 0x80, 0x18, CC, SS1, ..., SS23, CRC_low, CRC_high };
+4) host reads response: { 0xfe, 0x41, 0x81, 0xe0 };
+5) host waits until rdy signal goes high: RDY = 1;
+6) host writes command "read 44 bytes starting from adress 0x0080": { 0xfe, 0x44, 0x00, 0x80, 0x2c, CRC_low, CRC_high };
+7) host reads response: { 0xfe, 0x44, 0x2c, 0x00, SS1, SS2, ..., SS23, PP_H, PP_L, D1, D2, ..., D18, CRC_low, CRC_high };
+8) host powers down sensor: VBB_EN = 0;
+
+
+--------------------------------------------------------------------------------
+--------------------------------------------------------------------------------
+CC = Calculation Control, 1 byte
+SS = Sensor State, Sensor State, 23 bytes
+D = Measured data and Sensor Status, 23 bytes
+PP = Host Pressure Value
+CRC= 16 bit CRC error check
+--------------------------------------------------------------------------------
+--------------------------------------------------------------------------------
+*/
+