diff --git a/sonoff/i18n.h b/sonoff/i18n.h
index b1bec3289..2347cba22 100644
--- a/sonoff/i18n.h
+++ b/sonoff/i18n.h
@@ -548,7 +548,7 @@ const char HTTP_SNS_SEAPRESSURE[] PROGMEM = "%s{s}%s " D_PRESSUREATSEALEVEL "{m}
 const char HTTP_SNS_ANALOG[] PROGMEM = "%s{s}%s " D_ANALOG_INPUT "%d{m}%d{e}";                               // {s} = <tr><th>, {m} = </th><td>, {e} = </td></tr>
 const char HTTP_SNS_ILLUMINANCE[] PROGMEM = "%s{s}%s " D_ILLUMINANCE "{m}%d " D_UNIT_LUX "{e}";              // {s} = <tr><th>, {m} = </th><td>, {e} = </td></tr>
 
-#if defined(USE_MHZ19) || defined(USE_SENSEAIR)
+#if defined(USE_MHZ19) || defined(USE_SENSEAIR) || defined(USE_AZ7798)
 const char HTTP_SNS_CO2[] PROGMEM = "%s{s}%s " D_CO2 "{m}%d " D_UNIT_PARTS_PER_MILLION "{e}";                // {s} = <tr><th>, {m} = </th><td>, {e} = </td></tr>
 #endif  // USE_WEBSERVER
 
diff --git a/sonoff/language/bg-BG.h b/sonoff/language/bg-BG.h
index 6a2265f1a..222c62b58 100644
--- a/sonoff/language/bg-BG.h
+++ b/sonoff/language/bg-BG.h
@@ -538,6 +538,8 @@
 #define D_SENSOR_SSPI_CS   "SSPI CS"
 #define D_SENSOR_SSPI_DC   "SSPI DC"
 #define D_SENSOR_RF_SENSOR "RF датчик"
+#define D_SENSOR_AZ_RX   "AZ Rx"
+#define D_SENSOR_AZ_TX   "AZ Tx"
 
 // Units
 #define D_UNIT_AMPERE "A"
diff --git a/sonoff/language/cs-CZ.h b/sonoff/language/cs-CZ.h
index 461de3a4d..45f55af6a 100644
--- a/sonoff/language/cs-CZ.h
+++ b/sonoff/language/cs-CZ.h
@@ -538,6 +538,8 @@
 #define D_SENSOR_SSPI_CS   "SSPI CS"
 #define D_SENSOR_SSPI_DC   "SSPI DC"
 #define D_SENSOR_RF_SENSOR "RF Sensor"
+#define D_SENSOR_AZ_RX   "AZ Rx"
+#define D_SENSOR_AZ_TX   "AZ Tx"
 
 // Units
 #define D_UNIT_AMPERE "A"
diff --git a/sonoff/language/de-DE.h b/sonoff/language/de-DE.h
index 293de0830..23d8de9ed 100644
--- a/sonoff/language/de-DE.h
+++ b/sonoff/language/de-DE.h
@@ -538,6 +538,8 @@
 #define D_SENSOR_SSPI_CS   "SSPI CS"
 #define D_SENSOR_SSPI_DC   "SSPI DC"
 #define D_SENSOR_RF_SENSOR "RF Sensor"
+#define D_SENSOR_AZ_RX   "AZ Rx"
+#define D_SENSOR_AZ_TX   "AZ Tx"
 
 // Units
 #define D_UNIT_AMPERE "A"
diff --git a/sonoff/language/el-GR.h b/sonoff/language/el-GR.h
index 2148baf42..a8b48ed35 100644
--- a/sonoff/language/el-GR.h
+++ b/sonoff/language/el-GR.h
@@ -538,6 +538,8 @@
 #define D_SENSOR_SSPI_CS   "SSPI CS"
 #define D_SENSOR_SSPI_DC   "SSPI DC"
 #define D_SENSOR_RF_SENSOR "RF Sensor"
+#define D_SENSOR_AZ_RX   "AZ Rx"
+#define D_SENSOR_AZ_TX   "AZ Tx"
 
 // Units
 #define D_UNIT_AMPERE "A"
diff --git a/sonoff/language/en-GB.h b/sonoff/language/en-GB.h
index 70825c5e3..2ea9c249a 100644
--- a/sonoff/language/en-GB.h
+++ b/sonoff/language/en-GB.h
@@ -538,6 +538,8 @@
 #define D_SENSOR_SSPI_CS   "SSPI CS"
 #define D_SENSOR_SSPI_DC   "SSPI DC"
 #define D_SENSOR_RF_SENSOR "RF Sensor"
+#define D_SENSOR_AZ_RX   "AZ Rx"
+#define D_SENSOR_AZ_TX   "AZ Tx"
 
 // Units
 #define D_UNIT_AMPERE "A"
diff --git a/sonoff/language/es-AR.h b/sonoff/language/es-AR.h
index 011c7a248..435f230ad 100644
--- a/sonoff/language/es-AR.h
+++ b/sonoff/language/es-AR.h
@@ -538,6 +538,8 @@
 #define D_SENSOR_SSPI_CS   "SSPI CS"
 #define D_SENSOR_SSPI_DC   "SSPI DC"
 #define D_SENSOR_RF_SENSOR "RF Sensor"
+#define D_SENSOR_AZ_RX   "AZ Rx"
+#define D_SENSOR_AZ_TX   "AZ Tx"
 
 // Units
 #define D_UNIT_AMPERE "A"
diff --git a/sonoff/language/fr-FR.h b/sonoff/language/fr-FR.h
index 642b4686d..0638b408a 100644
--- a/sonoff/language/fr-FR.h
+++ b/sonoff/language/fr-FR.h
@@ -538,6 +538,8 @@
 #define D_SENSOR_SSPI_CS   "SSPI CS"
 #define D_SENSOR_SSPI_DC   "SSPI DC"
 #define D_SENSOR_RF_SENSOR "RF Sensor"
+#define D_SENSOR_AZ_RX   "AZ Rx"
+#define D_SENSOR_AZ_TX   "AZ Tx"
 
 // Units
 #define D_UNIT_AMPERE "A"
diff --git a/sonoff/language/he-HE.h b/sonoff/language/he-HE.h
index 7dc8585db..cd1b0e92e 100644
--- a/sonoff/language/he-HE.h
+++ b/sonoff/language/he-HE.h
@@ -538,6 +538,8 @@
 #define D_SENSOR_SSPI_CS   "SSPI CS"
 #define D_SENSOR_SSPI_DC   "SSPI DC"
 #define D_SENSOR_RF_SENSOR "RF Sensor"
+#define D_SENSOR_AZ_RX   "AZ Rx"
+#define D_SENSOR_AZ_TX   "AZ Tx"
 
 // Units
 #define D_UNIT_AMPERE "A"
diff --git a/sonoff/language/hu-HU.h b/sonoff/language/hu-HU.h
index 707bb24ec..244d55776 100644
--- a/sonoff/language/hu-HU.h
+++ b/sonoff/language/hu-HU.h
@@ -538,6 +538,8 @@
 #define D_SENSOR_SSPI_CS   "SSPI CS"
 #define D_SENSOR_SSPI_DC   "SSPI DC"
 #define D_SENSOR_RF_SENSOR "RF Sensor"
+#define D_SENSOR_AZ_RX   "AZ Rx"
+#define D_SENSOR_AZ_TX   "AZ Tx"
 
 // Units
 #define D_UNIT_AMPERE "A"
diff --git a/sonoff/language/it-IT.h b/sonoff/language/it-IT.h
index d2e277a8c..a6d0d693c 100644
--- a/sonoff/language/it-IT.h
+++ b/sonoff/language/it-IT.h
@@ -538,6 +538,8 @@
 #define D_SENSOR_SSPI_CS   "SSPI CS"
 #define D_SENSOR_SSPI_DC   "SSPI DC"
 #define D_SENSOR_RF_SENSOR "RF Sensor"
+#define D_SENSOR_AZ_RX   "AZ Rx"
+#define D_SENSOR_AZ_TX   "AZ Tx"
 
 // Units
 #define D_UNIT_AMPERE "A"
diff --git a/sonoff/language/nl-NL.h b/sonoff/language/nl-NL.h
index 3383228ed..b3bf10989 100644
--- a/sonoff/language/nl-NL.h
+++ b/sonoff/language/nl-NL.h
@@ -538,6 +538,8 @@
 #define D_SENSOR_SSPI_CS   "SSPI CS"
 #define D_SENSOR_SSPI_DC   "SSPI DC"
 #define D_SENSOR_RF_SENSOR "RF Sensor"
+#define D_SENSOR_AZ_RX   "AZ Rx"
+#define D_SENSOR_AZ_TX   "AZ Tx"
 
 // Units
 #define D_UNIT_AMPERE "A"
diff --git a/sonoff/language/pl-PL.h b/sonoff/language/pl-PL.h
index 0019c8d53..d80826751 100644
--- a/sonoff/language/pl-PL.h
+++ b/sonoff/language/pl-PL.h
@@ -538,6 +538,8 @@
 #define D_SENSOR_SSPI_CS   "SSPI CS"
 #define D_SENSOR_SSPI_DC   "SSPI DC"
 #define D_SENSOR_RF_SENSOR "RF Sensor"
+#define D_SENSOR_AZ_RX   "AZ Rx"
+#define D_SENSOR_AZ_TX   "AZ Tx"
 
 // Units
 #define D_UNIT_AMPERE "A"
diff --git a/sonoff/language/pt-BR.h b/sonoff/language/pt-BR.h
index e8e536606..7add978f0 100644
--- a/sonoff/language/pt-BR.h
+++ b/sonoff/language/pt-BR.h
@@ -538,6 +538,8 @@
 #define D_SENSOR_SSPI_CS   "SSPI CS"
 #define D_SENSOR_SSPI_DC   "SSPI DC"
 #define D_SENSOR_RF_SENSOR "RF Sensor"
+#define D_SENSOR_AZ_RX   "AZ Rx"
+#define D_SENSOR_AZ_TX   "AZ Tx"
 
 // Units
 #define D_UNIT_AMPERE "A"
diff --git a/sonoff/language/pt-PT.h b/sonoff/language/pt-PT.h
index 58a39fff0..9869762b8 100644
--- a/sonoff/language/pt-PT.h
+++ b/sonoff/language/pt-PT.h
@@ -538,6 +538,8 @@
 #define D_SENSOR_SSPI_CS   "SSPI CS"
 #define D_SENSOR_SSPI_DC   "SSPI DC"
 #define D_SENSOR_RF_SENSOR "RF Sensor"
+#define D_SENSOR_AZ_RX   "AZ Rx"
+#define D_SENSOR_AZ_TX   "AZ Tx"
 
 // Units
 #define D_UNIT_AMPERE "A"
diff --git a/sonoff/language/ru-RU.h b/sonoff/language/ru-RU.h
index 85813373a..d0a3f6933 100644
--- a/sonoff/language/ru-RU.h
+++ b/sonoff/language/ru-RU.h
@@ -538,6 +538,8 @@
 #define D_SENSOR_SSPI_CS   "SSPI CS"
 #define D_SENSOR_SSPI_DC   "SSPI DC"
 #define D_SENSOR_RF_SENSOR "RF Sensor"
+#define D_SENSOR_AZ_RX   "AZ Rx"
+#define D_SENSOR_AZ_TX   "AZ Tx"
 
 // Units
 #define D_UNIT_AMPERE "А"
diff --git a/sonoff/language/sk-SK.h b/sonoff/language/sk-SK.h
index a01fa1b3e..f46372426 100644
--- a/sonoff/language/sk-SK.h
+++ b/sonoff/language/sk-SK.h
@@ -538,6 +538,8 @@
 #define D_SENSOR_SSPI_CS   "SSPI CS"
 #define D_SENSOR_SSPI_DC   "SSPI DC"
 #define D_SENSOR_RF_SENSOR "RF Senzor"
+#define D_SENSOR_AZ_RX   "AZ Rx"
+#define D_SENSOR_AZ_TX   "AZ Tx"
 
 // Units
 #define D_UNIT_AMPERE "A"
diff --git a/sonoff/language/sv-SE.h b/sonoff/language/sv-SE.h
index 4ae68e78c..f36162a4b 100644
--- a/sonoff/language/sv-SE.h
+++ b/sonoff/language/sv-SE.h
@@ -538,6 +538,8 @@
 #define D_SENSOR_SSPI_CS   "SSPI CS"
 #define D_SENSOR_SSPI_DC   "SSPI DC"
 #define D_SENSOR_RF_SENSOR "RF Sensor"
+#define D_SENSOR_AZ_RX   "AZ Rx"
+#define D_SENSOR_AZ_TX   "AZ Tx"
 
 // Units
 #define D_UNIT_AMPERE "A"
diff --git a/sonoff/language/tr-TR.h b/sonoff/language/tr-TR.h
index 43acbaa77..06d82b9cb 100755
--- a/sonoff/language/tr-TR.h
+++ b/sonoff/language/tr-TR.h
@@ -538,6 +538,8 @@
 #define D_SENSOR_SSPI_CS   "SSPI CS"
 #define D_SENSOR_SSPI_DC   "SSPI DC"
 #define D_SENSOR_RF_SENSOR "RF Sensor"
+#define D_SENSOR_AZ_RX   "AZ Rx"
+#define D_SENSOR_AZ_TX   "AZ Tx"
 
 // Units
 #define D_UNIT_AMPERE "A"
diff --git a/sonoff/language/uk-UK.h b/sonoff/language/uk-UK.h
index a924a6cf4..509c90753 100644
--- a/sonoff/language/uk-UK.h
+++ b/sonoff/language/uk-UK.h
@@ -538,6 +538,8 @@
 #define D_SENSOR_SSPI_CS   "SSPI CS"
 #define D_SENSOR_SSPI_DC   "SSPI DC"
 #define D_SENSOR_RF_SENSOR "RF Sensor"
+#define D_SENSOR_AZ_RX   "AZ Rx"
+#define D_SENSOR_AZ_TX   "AZ Tx"
 
 // Units
 #define D_UNIT_AMPERE "А"
diff --git a/sonoff/language/zh-CN.h b/sonoff/language/zh-CN.h
index dfd5662e0..05bedca81 100644
--- a/sonoff/language/zh-CN.h
+++ b/sonoff/language/zh-CN.h
@@ -538,6 +538,8 @@
 #define D_SENSOR_SSPI_CS   "SSPI CS"
 #define D_SENSOR_SSPI_DC   "SSPI DC"
 #define D_SENSOR_RF_SENSOR "RF Sensor"
+#define D_SENSOR_AZ_RX   "AZ Rx"
+#define D_SENSOR_AZ_TX   "AZ Tx"
 
 // Units
 #define D_UNIT_AMPERE "安"
diff --git a/sonoff/language/zh-TW.h b/sonoff/language/zh-TW.h
index abc3df93d..2780181aa 100644
--- a/sonoff/language/zh-TW.h
+++ b/sonoff/language/zh-TW.h
@@ -538,6 +538,8 @@
 #define D_SENSOR_SSPI_CS   "SSPI CS"
 #define D_SENSOR_SSPI_DC   "SSPI DC"
 #define D_SENSOR_RF_SENSOR "RF Sensor"
+#define D_SENSOR_AZ_RX   "AZ Rx"
+#define D_SENSOR_AZ_TX   "AZ Tx"
 
 // Units
 #define D_UNIT_AMPERE "安"
diff --git a/sonoff/my_user_config.h b/sonoff/my_user_config.h
index cbc7a7790..aa92cba85 100644
--- a/sonoff/my_user_config.h
+++ b/sonoff/my_user_config.h
@@ -367,6 +367,7 @@
   #define TUYA_DIMMER_ID       0                 // Default dimmer Id
 #define USE_ARMTRONIX_DIMMERS                    // Add support for Armtronix Dimmers (+1k4 code)
 #define USE_PS_16_DZ                             // Add support for PS-16-DZ Dimmer
+//#define USE_AZ7798                               // Add support for AZ-Instrument 7798 CO2 datalogger (+1k6 code)
 
 // Power monitoring sensors -----------------------
 #define USE_PZEM004T                             // Add support for PZEM004T Energy monitor (+2k code)
diff --git a/sonoff/sonoff_post.h b/sonoff/sonoff_post.h
index f8798e454..8eddeea5b 100644
--- a/sonoff/sonoff_post.h
+++ b/sonoff/sonoff_post.h
@@ -135,6 +135,7 @@ void KNX_CB_Action(message_t const &msg, void *arg);
 #define USE_RF_SENSOR                         // Add support for RF sensor receiver (434MHz or 868MHz) (+0k8 code)
 //  #define USE_THEO_V2                         // Add support for decoding Theo V2 sensors as documented on https://sidweb.nl using 434MHz RF sensor receiver (+1k4 code)
   #define USE_ALECTO_V2                       // Add support for decoding Alecto V2 sensors like ACH2010, WS3000 and DKW2012 using 868MHz RF sensor receiver (+1k7 code)
+//#define USE_AZ7798                               // Add support for AZ-Instrument 7798 CO2 datalogger
 #endif  // USE_SENSORS
 
 /*********************************************************************************************\
@@ -193,6 +194,7 @@ void KNX_CB_Action(message_t const &msg, void *arg);
 #undef USE_RF_SENSOR                          // Disable support for RF sensor receiver (434MHz or 868MHz) (+0k8 code)
 #undef DEBUG_THEO                             // Disable debug code
 #undef USE_DEBUG_DRIVER                       // Disable debug code
+#undef USE_AZ7798                             // Disable support for AZ-Instrument 7798 CO2 datalogger
 #endif  // USE_CLASSIC
 
 /*********************************************************************************************\
@@ -313,6 +315,7 @@ void KNX_CB_Action(message_t const &msg, void *arg);
 #undef USE_RF_SENSOR                          // Disable support for RF sensor receiver (434MHz or 868MHz) (+0k8 code)
 #undef DEBUG_THEO                             // Disable debug code
 #undef USE_DEBUG_DRIVER                       // Disable debug code
+#undef USE_AZ7798                             // Disable support for AZ-Instrument 7798 CO2 datalogger
 #endif  // USE_BASIC
 
 /*********************************************************************************************\
@@ -375,6 +378,7 @@ void KNX_CB_Action(message_t const &msg, void *arg);
 #undef USE_RF_SENSOR                          // Disable support for RF sensor receiver (434MHz or 868MHz) (+0k8 code)
 #undef DEBUG_THEO                             // Disable debug code
 #undef USE_DEBUG_DRIVER                       // Disable debug code
+#undef USE_AZ7798                             // Disable support for AZ-Instrument 7798 CO2 datalogger
 #endif  // BE_MINIMAL
 
 /*********************************************************************************************\
diff --git a/sonoff/sonoff_template.h b/sonoff/sonoff_template.h
index 91eec21c7..48af9cf4b 100644
--- a/sonoff/sonoff_template.h
+++ b/sonoff/sonoff_template.h
@@ -141,6 +141,8 @@ enum UserSelectablePins {
   GPIO_SSPI_CS,        // Software SPI Chip Select
   GPIO_SSPI_DC,        // Software SPI Data or Command
   GPIO_RF_SENSOR,      // Rf receiver with sensor decoding
+  GPIO_AZ_TXD,         // AZ-Instrument 7798 Serial interface
+  GPIO_AZ_RXD,         // AZ-Instrument 7798 Serial interface
   GPIO_SENSOR_END };
 
 // Programmer selectable GPIO functionality offset by user selectable GPIOs
@@ -201,7 +203,8 @@ const char kSensorNames[] PROGMEM =
   D_SENSOR_TUYA_TX "|" D_SENSOR_TUYA_RX "|"
   D_SENSOR_MGC3130_XFER "|" D_SENSOR_MGC3130_RESET "|"
   D_SENSOR_SSPI_MISO "|" D_SENSOR_SSPI_MOSI "|" D_SENSOR_SSPI_SCLK "|" D_SENSOR_SSPI_CS "|" D_SENSOR_SSPI_DC "|"
-  D_SENSOR_RF_SENSOR;
+  D_SENSOR_RF_SENSOR "|"
+  D_SENSOR_AZ_TX "|" D_SENSOR_AZ_RX;
 
 /********************************************************************************************/
 
@@ -454,6 +457,10 @@ const uint8_t kGpioNiceList[] PROGMEM = {
   GPIO_MGC3130_XFER,
   GPIO_MGC3130_RESET
 #endif
+#ifdef USE_AZ7798
+  GPIO_AZ_TXD,         // AZ-Instrument 7798 CO2 datalogger Serial interface
+  GPIO_AZ_RXD          // AZ-Instrument 7798 CO2 datalogger Serial interface
+#endif
 };
 
 const uint8_t kModuleNiceList[MAXMODULE] PROGMEM = {
diff --git a/sonoff/support_features.ino b/sonoff/support_features.ino
index 652116b2f..75ddaf327 100644
--- a/sonoff/support_features.ino
+++ b/sonoff/support_features.ino
@@ -370,7 +370,9 @@ void GetFeatures(void)
 #ifdef USE_ALECTO_V2
   feature_sns2 |= 0x00020000;
 #endif
-//  feature_sns2 |= 0x00040000;
+#ifdef USE_AZ7798
+  feature_sns2 |= 0x00040000;
+#endif
 //  feature_sns2 |= 0x00080000;
 //  feature_sns2 |= 0x00100000;
 //  feature_sns2 |= 0x00200000;
diff --git a/sonoff/xsns_38_az7798.ino b/sonoff/xsns_38_az7798.ino
new file mode 100644
index 000000000..6491be885
--- /dev/null
+++ b/sonoff/xsns_38_az7798.ino
@@ -0,0 +1,304 @@
+/*
+  xsns_38_az7798.ino - AZ_Instrument 7798 CO2/temperature/humidity meter support for Sonoff-Tasmota
+
+  Copyright (C) 2018  Theo Arends
+
+  This program is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifdef USE_AZ7798
+
+#define XSNS_38 38
+
+/*********************************************************************************************\
+ * CO2, temperature and humidity meter and data logger
+ * Known by different names (brief survey 2018-12-16):
+ *  - AZ-Instrument 7798 (http://www.az-instrument.com.tw)
+ *  - co2meter.com AZ-0004
+ *  - Extech CO200
+ *  - BES CO7788 (https://www.aliexpress.com)
+ *  - AZ CO87 (https://www.aliexpress.com)
+ *  - no doubt there are more ...
+ *
+ * Hardware Serial will be selected if GPIO1 = [AZ Tx] and GPIO3 = [AZ Rx]
+ *
+ * Inside the meter, the serial comms wire with the red stripe goes to GPIO1.
+ * The other one therefore to GPIO3.
+ * WeMos D1 Mini is powered from the incoming 5V.
+ *
+ * This implementation was derived from xsns_15_mhz19.ino from
+ * Sonoff-Tasmota-6.3.0 by Arthur de Beun.
+ *
+ * The serial comms protocol is not publicly documented, that I could find.
+ * The info below was obtained by reverse-engineering.
+ * Port settings: 9600 8N1
+ * The suppied USB interface has a CP20x USB-serial bridge.
+ * The 3-way, 2.5mm jack has tip=RxD, middle=TxD and base=0V
+ * The TxD output swing is 3V3.
+ *
+ * There is never a space before the 0x0d, but the other spaces are there.
+ *
+ * serial number / ID
+ *   request:  I 0x0d
+ *   response: i 12345678 7798V3.4 0x0d
+ *
+ * log info
+ *   request:  M 0x0d
+ *   response: m 45 1 C 1af4 0cf4 0x0d
+ *
+ *             45 = number of records, but there are only 15 lines of 3 values each)
+ *              1 = sample rate in seconds
+ *              C = celcius, F
+ *      1af4 0cf4 = seconds since 2000-01-01 00:00:00
+ *
+ *          start time 2014-04-30 19:35:16
+ *          end time   2014-04-30 19:35:30
+ *
+ * download log data
+ *   request:  D 0x0d
+ *   response: m 45 1 C 1af4 0cf4 0x0d
+ *             d 174 955 698 0x0d
+ *               174 = temp in [C * 10]
+ *               955 = CO2 [ppm]
+ *               698 = RH in [% * 10]
+ *             d 174 990 694 0x0d
+ *       ...
+ *             d 173 929 654 0x0d
+ *
+ *            15 lines in total, 1 second apart
+ *
+ * Sync datalogger time with PC
+ *   request:  C 452295746 0x0d
+ *   response: > 0x0d
+ *
+ *              452295746 = seconds since 2000-01-01 00:00:00
+ *
+ * Identifier:
+ *   request:  J -------- 1 0x0d
+ *
+ *             the characters (dashes) in the above become the first part of the response to the I command (12345678 above)
+ *
+ * Set sample rate
+ *   request:  S 10 0x0d
+ *   response: m 12 10 C 1af5 7be1 0x0d
+ *
+ * Other characters that seem to give a response:
+ * A  responds with >
+ *    so is similar to the response to C, so other characters may be required
+ *    A is the beep alarm perhaps?
+ *    parameters would be CO2 level and on/off, as per front panel P1.3 setting?
+ *
+ * L  responds with >
+ *    L perhaps sets the limits for the good and normal levels (P1.1 and P1.2)?
+ *
+ * Q  responds with >
+ *    Q is reset maybe (P4.1)?
+ *
+ * :  responds with : T19.9C:C2167ppm:H57.4%
+ *    This one gives the current readings.
+ **********************************************************************************************
+
+/*********************************************************************************************/
+
+#include <TasmotaSerial.h>
+
+#ifndef CO2_LOW
+#define CO2_LOW                      800     // Below this CO2 value show green light
+#endif
+#ifndef CO2_HIGH
+#define CO2_HIGH                     1200    // Above this CO2 value show red light
+#endif
+
+#define AZ_READ_TIMEOUT              400     // Must be way less than 1000 but enough to read 9 bytes at 9600 bps
+
+TasmotaSerial *AzSerial;
+
+const char ktype[] = "AZ7798";
+uint8_t az_type = 1;
+uint16_t az_co2 = 0;
+double az_temperature = 0;
+double az_humidity = 0;
+uint8_t az_received = 0;
+uint8_t az_state = 0;
+
+/*********************************************************************************************/
+
+void AzEverySecond(void)
+{
+  az_state++;
+  if (5 == az_state) {                      // every 5 seconds
+    az_state = 0;
+
+    AzSerial->flush();                      // sync reception
+    AzSerial->write(":\r", 2);
+    az_received = 0;
+
+    uint8_t az_response[32];
+    unsigned long start = millis();
+    uint8_t counter = 0;
+    uint8_t i, j;
+    uint8_t response_substr[16];
+
+    do {
+      if (AzSerial->available() > 0) {
+        az_response[counter] = AzSerial->read();
+        if(az_response[counter] == 0x0d) { az_received = 1; }
+        counter++;
+      } else {
+        delay(5);
+      }
+    } while(((millis() - start) < AZ_READ_TIMEOUT) && (counter < sizeof(az_response)) && !az_received);
+
+    AddLogSerial(LOG_LEVEL_DEBUG_MORE, az_response, counter);
+
+    if (!az_received) {
+      AddLog_P(LOG_LEVEL_DEBUG, PSTR(D_LOG_DEBUG "AZ7798 comms timeout"));
+      return;
+    }
+
+    i = 0;
+    while((az_response[i] != 'T') && (i < counter)) {i++;} // find the start of response
+    if(az_response[i] != 'T') {
+      AddLog_P(LOG_LEVEL_DEBUG, PSTR(D_LOG_DEBUG "AZ7798 failed to find start of response"));
+      return;
+    }
+    i++;                                    // advance to start of temperature value
+    j = 0;
+    // find the end of temperature
+    while((az_response[i] != 'C') && (az_response[i] != 'F') && (i < counter)) {
+      response_substr[j++] = az_response[i++];
+    }
+    if((az_response[i] != 'C') && (az_response[i] != 'F')){
+      AddLog_P(LOG_LEVEL_DEBUG, PSTR(D_LOG_DEBUG "AZ7798 failed to find end of temperature"));
+      return;
+    }
+    response_substr[j] = 0;                 // add null terminator
+    az_temperature = CharToDouble((char*)response_substr); // units (C or F) depends on meter setting
+    if(az_response[i] == 'C') {             // meter transmits in degC
+      az_temperature = ConvertTemp((float)az_temperature); // convert to degF, depending on settings
+    } else {                                // meter transmits in degF
+      az_temperature = ConvertTemp((az_temperature - 32) / 1.8); // convert to degC and then C or F depending on setting
+    }
+    i++;                                    // advance to first delimiter
+    if(az_response[i] != ':') {
+      AddLog_P(LOG_LEVEL_DEBUG, PSTR(D_LOG_DEBUG "AZ7798 error first delimiter"));
+      return;
+    }
+    i++;                                    // advance to start of CO2
+    if(az_response[i] != 'C') {
+      AddLog_P(LOG_LEVEL_DEBUG, PSTR(D_LOG_DEBUG "AZ7798 error start of CO2"));
+      return;
+    }
+    i++;                                    // advance to start of CO2 value
+    j = 0;
+    // find the end of CO2
+    while((az_response[i] != 'p') && (i < counter)) {
+      response_substr[j++] = az_response[i++];
+    }
+    if(az_response[i] != 'p') {
+      AddLog_P(LOG_LEVEL_DEBUG, PSTR(D_LOG_DEBUG "AZ7798 failed to find end of CO2"));
+      return;
+    }
+    response_substr[j] = 0;                 // add null terminator
+    az_co2 = atoi((char*)response_substr);
+    LightSetSignal(CO2_LOW, CO2_HIGH, az_co2);
+    i += 3;                                 // advance to second delimiter
+    if(az_response[i] != ':') {
+      AddLog_P(LOG_LEVEL_DEBUG, PSTR(D_LOG_DEBUG "AZ7798 error second delimiter"));
+      return;
+    }
+    i++;                                    // advance to start of humidity
+    if(az_response[i] != 'H') {
+      AddLog_P(LOG_LEVEL_DEBUG, PSTR(D_LOG_DEBUG "AZ7798 error start of humidity"));
+      return;
+    }
+    i++;                                    // advance to start of humidity value
+    j = 0;
+    // find the end of humidity
+    while((az_response[i] != '%') && (i < counter)) {
+      response_substr[j++] = az_response[i++];
+    }
+    if(az_response[i] != '%') {
+      AddLog_P(LOG_LEVEL_DEBUG, PSTR(D_LOG_DEBUG "AZ7798 failed to find end of humidity"));
+      return;
+    }
+    response_substr[j] = 0;                 // add null terminator
+    az_humidity = CharToDouble((char*)response_substr);
+  }
+}
+
+/*********************************************************************************************/
+
+void AzInit(void)
+{
+  az_type = 0;
+  if ((pin[GPIO_AZ_RXD] < 99) && (pin[GPIO_AZ_TXD] < 99)) {
+    AzSerial = new TasmotaSerial(pin[GPIO_AZ_RXD], pin[GPIO_AZ_TXD], 1);
+    if (AzSerial->begin(9600)) {
+      if (AzSerial->hardwareSerial()) { ClaimSerial(); }
+      az_type = 1;
+    }
+  }
+}
+
+void AzShow(boolean json)
+{
+  char temperature[10], humidity[10];
+  dtostrfd(az_temperature, Settings.flag2.temperature_resolution, temperature);
+  dtostrfd(az_humidity, Settings.flag2.humidity_resolution, humidity);
+
+  if (json) {
+    snprintf_P(mqtt_data, sizeof(mqtt_data), PSTR("%s,\"%s\":{\"" D_JSON_CO2 "\":%d,\"" D_JSON_TEMPERATURE "\":%s,\"" D_JSON_HUMIDITY "\":%s}"), mqtt_data, ktype, az_co2, temperature, humidity);
+#ifdef USE_DOMOTICZ
+    if (0 == tele_period) DomoticzSensor(DZ_AIRQUALITY, az_co2);
+#endif  // USE_DOMOTICZ
+#ifdef USE_WEBSERVER
+  } else {
+    snprintf_P(mqtt_data, sizeof(mqtt_data), HTTP_SNS_CO2, mqtt_data, ktype, az_co2);
+    snprintf_P(mqtt_data, sizeof(mqtt_data), HTTP_SNS_TEMP, mqtt_data, ktype, temperature, TempUnit());
+    snprintf_P(mqtt_data, sizeof(mqtt_data), HTTP_SNS_HUM, mqtt_data, ktype, humidity);
+#endif  // USE_WEBSERVER
+  }
+}
+
+/*********************************************************************************************\
+ * Interface
+\*********************************************************************************************/
+
+boolean Xsns38(byte function)
+{
+  boolean result = false;
+
+  if(az_type){
+    switch (function) {
+      case FUNC_INIT:
+        AzInit();
+        break;
+      case FUNC_EVERY_SECOND:
+        AzEverySecond();
+        break;
+      case FUNC_JSON_APPEND:
+        AzShow(1);
+        break;
+#ifdef USE_WEBSERVER
+      case FUNC_WEB_APPEND:
+        AzShow(0);
+        break;
+#endif  // USE_WEBSERVER
+    }
+  }
+  return result;
+}
+
+#endif  // USE_AZ7798
diff --git a/tools/decode-status.py b/tools/decode-status.py
index fa108bc02..ce8be9131 100644
--- a/tools/decode-status.py
+++ b/tools/decode-status.py
@@ -135,7 +135,7 @@ a_features = [[
     "USE_MCP230xx_OUTPUT","USE_MCP230xx_DISPLAYOUTPUT","USE_HLW8012","USE_CSE7766",
     "USE_MCP39F501","USE_PZEM_AC","USE_DS3231","USE_HX711",
     "USE_PZEM_DC","USE_TX20_WIND_SENSOR","USE_MGC3130","USE_RF_SENSOR",
-    "USE_THEO_V2","USE_ALECTO_V2","","",
+    "USE_THEO_V2","USE_ALECTO_V2","USE_AZ7798","",
     "","","","",
     "","","","",
     "","","",""]]