From 0180a0342ff3c68048357e8971d18ec4d7a11eea Mon Sep 17 00:00:00 2001
From: Stefan Brand <seiichiro@seiichiro0185.org>
Date: Tue, 2 Feb 2021 21:12:31 +0100
Subject: [PATCH] Add Some Prototype Code for the SG112A/B CO2 Sensor

---
 lib/SG112A/SG112A.cpp | 69 ++++++++++++++++++++++++++++++++++++++-----
 lib/SG112A/SG112A.h   | 16 ++++++++--
 src/config.h.example  |  3 ++
 src/main.cpp          |  5 +++-
 4 files changed, 83 insertions(+), 10 deletions(-)

diff --git a/lib/SG112A/SG112A.cpp b/lib/SG112A/SG112A.cpp
index ccf3add..daf8802 100644
--- a/lib/SG112A/SG112A.cpp
+++ b/lib/SG112A/SG112A.cpp
@@ -1,22 +1,77 @@
 #include <Arduino.h>
 #include "SG112A.h"
 
-void GA112A(void) {
-  
+SG112A::SG112A(void) {
+    Serial.begin(9600);
+    Serial.setTimeout(READ_TIMEOUT);
+    delay(5000);
+    write(CMD_GET_PPM);
+    read();
 }
 
 void SG112A::getSensorData(lora_data &loradata) {
+    write(CMD_GET_PPM);
+    delay(50);
+    uint8_t byteLen = read();
 
+    if (byteLen > 0) {
+        switch(buffer[3]) {
+            case 0x15:
+                loradata.ppm = (buffer[5]*256) + buffer[4];
+                break;
+        }
+    }
 }
 
-uint16_t SG112A::getPPM(void) {
-  
+void SG112A::write(byte cmd) {
+    uint8_t _cmd[6] = {0xAA, 0x55, cmd, 0x00, 0x00, 0x00};
+    uint16_t crc = crc16(_cmd, 4);
+    _cmd[4] = (uint8_t)(crc & 0xFF);
+    _cmd[5] = (uint8_t)(crc >> 8);
+    while (Serial.available() > 0) Serial.read();
+    Serial.write(_cmd, 6);
+    Serial.flush();
 }
 
-void SG112A::sendCmd(uint8_t *cmd, uint8_t len) {
+uint8_t SG112A::read() {
+    uint8_t ret = 0;
+    zeroBuffer();
+    if (Serial.available() > 0) {
+      ret = Serial.readBytes(buffer, SER_BUF_LEN);
+    }
 
+    if (buffer[0] != 0xBB && buffer[1] != 0x66)
+        ret = 0;
+
+    // TODO: Do CRC Check Here
+
+    return ret;
 }
 
-uint16_t SG112A::crc16(uint8_t *cmd, uint8_t len){
-  
+void SG112A::zeroBuffer() {
+    for (int i=0; i < SER_BUF_LEN; i++)
+        buffer[i] = 0x00;
+}
+
+uint16_t SG112A::crc16(uint8_t *cmd, int len){
+  uint16_t ret = 0xffff;
+  uint16_t polynomial = 0xa001;
+  int shift = 0x0;
+  int i = 0;
+  for (i = len - 1; i >= 0 ; i-- ){
+    
+    uint16_t code = ( uint16_t )( cmd [ len -1 - i ]  & 0xff );
+    ret = ret^code;
+    shift = 0x0;
+    while ( shift <= 7 ){           
+      if ( ret & 0x1 ) {                     
+        ret = ret >> 1;                     
+        ret = ret^polynomial ;
+      } else {
+        ret = ret >> 1;
+      }
+      shift++;
+    }
+  }      
+  return ret;
 }
diff --git a/lib/SG112A/SG112A.h b/lib/SG112A/SG112A.h
index bd7c617..df42d90 100644
--- a/lib/SG112A/SG112A.h
+++ b/lib/SG112A/SG112A.h
@@ -6,11 +6,23 @@ struct lora_data {
   int16_t ppm;
 } __attribute__ ((packed));
 
+#define READ_TIMEOUT 500
+#define SER_BUF_LEN  16
+
+#define CMD_GET_VER 0x10
+#define CMD_GET_SER 0x12
+#define CMD_GET_PPM 0x14
+
 class SG112A {
   private:
-    void sendCmd(uint8_t *cmd, uint8_t len);
-    uint16_t crc16(uint8_t *cmd, uint8_t len);
+    uint8_t buffer[SER_BUF_LEN];
+
+    void write(byte cmd);
+    uint8_t read();
+    void zeroBuffer(void);
+    uint16_t crc16(uint8_t *cmd, int len);
     uint16_t getPPM(void);
+
   public:
     SG112A(void);
     void getSensorData(lora_data &loradata);
diff --git a/src/config.h.example b/src/config.h.example
index 9fc253f..3bc075a 100644
--- a/src/config.h.example
+++ b/src/config.h.example
@@ -3,11 +3,14 @@
 #define LED_PIN PIN_PA7
 
 // Enable Serial Debugging. Parameters for the Serial Port are 115200
+// Please be aware that the SG112A/B CO2 Sensor uses the HW-UART, so
+// Serial Debug Output is not available with this Sensor.
 // #define DEBUG
 
 // Define which Sensor is installed
 #define HAS_BME280
 // #define HAS_SHT21
+// #define HAS_SG112A
 // #define HAS_NO_SENSOR
 
 // How many minutes to sleep between Measuring/Sending
diff --git a/src/main.cpp b/src/main.cpp
index b948b21..5950170 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -35,6 +35,9 @@ void blink(uint8_t num) {
   struct lora_data {
     uint8_t bat;
   } __attribute ((packed));
+#elif defined HAS_SG112A
+  #include <SG112A.h>
+  SG112A sensor;
 #elif defined HAS_BME280
   #include <BME280.h>
   BME280 sensor;
@@ -68,7 +71,7 @@ const lmic_pinmap lmic_pins = {
 };
 
 // List of unused Pins - will be disabled for Power Saving
-#ifdef DEBUG
+#if defined DEBUG || defined HAS_SG112A
 const int disabledPins[] = {PIN_PB5, PIN_PB4, PIN_PB1, PIN_PB0, PIN_PC3, PIN_PC2, PIN_PC1, PIN_PC0};
 #else
 const int disabledPins[] = {PIN_PB5, PIN_PB4, PIN_PB3, PIN_PB2, PIN_PB1, PIN_PB0, PIN_PC3, PIN_PC2, PIN_PC1, PIN_PC0};