HowTo: Tasmota – Sonoff S26 flashing with Tasmota firmware

In the search for cheap Wi-Fi sockets to control normal consumers you will sooner or later stumble on the “Sonoff S26”. This is a (if not the most) cheapest Wi-Fi socket I know.

The only downside to her is the firmware. This is not very universal and the functionality is limited. The solution to all these problems is the alternative firmware “Tasmota”. Thanks to it, the Sonoff S26 is extended to all the features that you miss with the standard firmware.

How you can proceed to flash the “Sonoff S26” with the Tasmota firmware is described in the following article.

Hints for our lovely english readers: Basically, many of the articles on are translations from the original german articles. Therefore, it may happen here and there that some illustrations are not available in english and that some translations are weird/strange/full of mistakes or generally totaly wrong. So if you find some obvious (or also not obvious) mistakes don't hesitate to leave us a hint about that in the comment section. 
Also please don't get confused, that instead of a "dot" often a "comma" is used as decimal separator. 🙂

Safety instructions

I know the following hints are always a bit annoying and seem unnecessary. But unfortunately, many people who knew it "better" from carelessness lost their eyes, fingers or other things or hurt themselves. In comparison, a loss of data is almost not worth mentioning, but even these can be really annoying. Therefore, please take five minutes to read the safety instructions. Even the coolest project is worth no injury or other annoyance.

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Helpful Articles:
Before you start with this article you should have dealt with the basics of soldering. Information on this can be found in the following article.
Electronics – My friend the soldering iron

Required tools:

In the following list you will find all the tools you need to implement this article.

Required material:

In the following list you will find all the parts you need to implement this article.

Collect required parts

In the following picture you can see the parts of a Sonoff S26 socket.

Open housing

In order to transfer the Tasmota firmware to the ESP8266 of the socket, you must now first attach the connection cables to which you can then connect the programming adapter.

Open the housing of the socket by loosening the three screws on the underside.
Then you can lift the lid on the bottom …
…and disassemble the housing into its individual parts. This will also bring you to the control board of the socket.

Prepare programming connections

To connect the programming adapter to the control board’s ESP8266, you must now solder a few leads to the control board.

The control board is the board which protrudes laterally from the large board and is connected to it only via three solder joints.
There are several small solder pads on the control board. In order to connect the programming adapter, you need to solder some wires to the solder pads “3V3”, “GND”, “ETX” and “ERX”.
To do this, you tin the solder pads as shown. This makes soldering the connection cables easier in the next step.
Solder the connection cables to the solder pads. Make sure that there are no short circuits (connections) between the soldering pads.
Closeup of soldered connection cables.
Closeup of soldered connection wires.
Closeup of soldered connection cables.

Connect programming interface

Now it’s time to connect the programming adapter to the controller board. There are many programming adapters, which is why their looks often different.

But there are always the PINs with the names “3V3”, “GND”, “TXD” and “RXD” available. These are the connections you need to connect the programming adapter to the controller board.

To do this, connect the Dupont lines to the four connection pins “3V3”, “GND”, “RX” and “TX” of the programming adapter.
The Dupont leads must now be connected to the leads you previously soldered to the control board. You have to connect the contacts “3V3” and “GND” with their respective counterparts. So “3V3” on the programming adapter with “3V3” on the control board and “GND” on the programming adapter with “GND” on the control board. The contacts “RX” and “TX” must be connected exactly “crosswise”. For this, connect “RX” of the programming adapter with “ETX” of the control board and “TX” of the programming adapter with “ERX” of the control board.
You can also understand the correct connections based on the colors of the lines.

Flash Tasmota firmware

After connecting your programming adapter to the controller board, flash the Tasmota firmware. This and the setting options are described in detail in the article Tasmota – Flashing Firmware.

The following is a configuration that should work for the Sonoff S26. Of course, you have to configure the access data for your Wi-Fi and, if necessary, the access data for your MQTT server.

  user_config.h - user specific configuration 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
  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 <>.

#ifndef _USER_CONFIG_H_
#define _USER_CONFIG_H_

 * This file consists of TWO sections.
 * The first section contains PARAMETERS overriding flash settings if define CFG_HOLDER is CHANGED.
 * All parameters can be persistent changed online using commands via MQTT, WebConsole or Serial.
 *   Corresponding MQTT/Serial/Console commands are shown in [brackets]
 * The second section contains Enabled and Disabled FEATURES allowing different program size.
 *   Changes in this section do NOT need a change of define CFG_HOLDER.
 * Users are advised to use the user_config_override.h file for most changes.

//#define USE_CONFIG_OVERRIDE                      // Uncomment to use user_config_override.h file. See

 * - After initial load any change here only take effect if CFG_HOLDER is changed too

// -- Master parameter control --------------------
#define CFG_HOLDER             4617              // [Reset 1] Change this value (max 32000) to load SECTION1 configuration parameters to flash

// -- Project -------------------------------------
#define PROJECT                "SonoffS26"          // PROJECT is used as the default topic delimiter
#define MODULE                 SONOFF_S2X      // [Module] Select default model from sonoff_template.h (Should not be changed)

#define SAVE_DATA              1                 // [SaveData] Save changed parameters to Flash (0 = disable, 1 - 3600 seconds)
#define SAVE_STATE             1                 // [SetOption0] Save changed power state to Flash (0 = disable, 1 = enable)

// -- Wifi ----------------------------------------
#define WIFI_IP_ADDRESS        ""         // [IpAddress1] Set to for using DHCP or IP address
#define WIFI_GATEWAY           ""   // [IpAddress2] If not using DHCP set Gateway IP address
#define WIFI_SUBNETMASK        ""   // [IpAddress3] If not using DHCP set Network mask
#define WIFI_DNS               ""    // [IpAddress4] If not using DHCP set DNS IP address (might be equal to WIFI_GATEWAY)

#define STA_SSID1              ""                // [Ssid1] Wifi SSID
#define STA_PASS1              ""                // [Password1] Wifi password
#define STA_SSID2              ""                // [Ssid2] Optional alternate AP Wifi SSID
#define STA_PASS2              ""                // [Password2] Optional alternate AP Wifi password
#define WIFI_CONFIG_TOOL       WIFI_MANAGER         // [WifiConfig] Default tool if wifi fails to connect
#define WIFI_CONFIG_NO_SSID    WIFI_WPSCONFIG    // Default tool if wifi fails to connect and no SSID is configured
                                                 //   (WIFI_SMARTCONFIG, WIFI_MANAGER, WIFI_WPSCONFIG, WIFI_SERIAL)
                                                 //   *** NOTE: When WPS is disabled by USE_WPS below, WIFI_WPSCONFIG will execute WIFI_MANAGER ***
                                                 //   *** NOTE: When WIFI_MANAGER is disabled by USE_WEBSERVER below, WIFI_MANAGER will execute WIFI_SMARTCONFIG ***
                                                 //   *** NOTE: When WIFI_SMARTCONFIG is disabled by USE_SMARTCONFIG below, WIFI_SMARTCONFIG will execute WIFI_SERIAL ***

// -- Syslog --------------------------------------
#define SYS_LOG_HOST           ""                // [LogHost] (Linux) syslog host
#define SYS_LOG_PORT           514               // [LogPort] default syslog UDP port

// -- Ota -----------------------------------------
#define OTA_URL                ""  // [OtaUrl]

// -- MQTT ----------------------------------------
#define MQTT_USE               1                 // [SetOption3] Select default MQTT use (0 = Off, 1 = On)

#define MQTT_HOST              "---"                // [MqttHost]
#define MQTT_FINGERPRINT1      "A5 02 FF 13 99 9F 8B 39 8E F1 83 4F 11 23 65 0B 32 36 FC 07"  // [MqttFingerprint1]
#define MQTT_FINGERPRINT2      "A5 02 FF 13 99 9F 8B 39 8E F1 83 4F 11 23 65 0B 32 36 FC 07"  // [MqttFingerprint2]
#define MQTT_PORT              1883              // [MqttPort] MQTT port (10123 on CloudMQTT)
#define MQTT_USER              "DVES_USER"       // [MqttUser] MQTT user
#define MQTT_PASS              "DVES_PASS"       // [MqttPassword] MQTT password

#define MQTT_BUTTON_RETAIN     0                 // [ButtonRetain] Button may send retain flag (0 = off, 1 = on)
#define MQTT_POWER_RETAIN      0                 // [PowerRetain] Power status message may send retain flag (0 = off, 1 = on)
#define MQTT_SWITCH_RETAIN     0                 // [SwitchRetain] Switch may send retain flag (0 = off, 1 = on)

#define MQTT_STATUS_OFF        "OFF"             // [StateText1] Command or Status result when turned off (needs to be a string like "0" or "Off")
#define MQTT_STATUS_ON         "ON"              // [StateText2] Command or Status result when turned on (needs to be a string like "1" or "On")
#define MQTT_CMND_TOGGLE       "TOGGLE"          // [StateText3] Command to send when toggling (needs to be a string like "2" or "Toggle")
#define MQTT_CMND_HOLD         "HOLD"            // [StateText4] Command to send when button is kept down for over KEY_HOLD_TIME * 0.1 seconds (needs to be a string like "HOLD")

// -- MQTT topics ---------------------------------
  // Example "tasmota/bedroom/%topic%/%prefix%/" up to 80 characers
#define MQTT_FULLTOPIC         "%prefix%/%topic%/" // [FullTopic] Subscribe and Publish full topic name - Legacy topic

// %prefix% token options
#define SUB_PREFIX             "cmnd"            // [Prefix1] Sonoff devices subscribe to %prefix%/%topic% being SUB_PREFIX/MQTT_TOPIC and SUB_PREFIX/MQTT_GRPTOPIC
#define PUB_PREFIX             "stat"            // [Prefix2] Sonoff devices publish to %prefix%/%topic% being PUB_PREFIX/MQTT_TOPIC
#define PUB_PREFIX2            "tele"            // [Prefix3] Sonoff devices publish telemetry data to %prefix%/%topic% being PUB_PREFIX2/MQTT_TOPIC/UPTIME, POWER and TIME
                                                 //   May be named the same as PUB_PREFIX
// %topic% token options (also ButtonTopic and SwitchTopic)
#define MQTT_TOPIC             PROJECT           // [Topic] (unique) MQTT device topic, set to 'PROJECT "_%06X"' for unique topic including device MAC address
#define MQTT_GRPTOPIC          "sonoffs"         // [GroupTopic] MQTT Group topic
#define MQTT_BUTTON_TOPIC      "0"               // [ButtonTopic] MQTT button topic, "0" = same as MQTT_TOPIC, set to 'PROJECT "_BTN_%06X"' for unique topic including device MAC address
#define MQTT_SWITCH_TOPIC      "0"               // [SwitchTopic] MQTT button topic, "0" = same as MQTT_TOPIC, set to 'PROJECT "_SW_%06X"' for unique topic including device MAC address
#define MQTT_CLIENT_ID         "DVES_%06X"       // [MqttClient] Also fall back topic using Chip Id = last 6 characters of MAC address

// -- MQTT - Telemetry ----------------------------
#define TELE_PERIOD            300               // [TelePeriod] Telemetry (0 = disable, 10 - 3600 seconds)

// -- MQTT - Domoticz -----------------------------
#define DOMOTICZ_UPDATE_TIMER  0                 // [DomoticzUpdateTimer] Send relay status (0 = disable, 1 - 3600 seconds)

// -- MQTT - Home Assistant Discovery -------------
#define HOME_ASSISTANT_DISCOVERY_ENABLE   0      // [SetOption19] Home Assistant Discovery (0 = Disable, 1 = Enable)

// -- HTTP ----------------------------------------
#define WEB_SERVER             2                 // [WebServer] Web server (0 = Off, 1 = Start as User, 2 = Start as Admin)
#define WEB_PASSWORD           ""                // [WebPassword] Web server Admin mode Password for WEB_USERNAME (empty string = Disable)
#define FRIENDLY_NAME          "SonoffS26"          // [FriendlyName] Friendlyname up to 32 characters used by webpages and Alexa
#define EMULATION              EMUL_NONE         // [Emulation] Select Belkin WeMo (single relay/light) or Hue Bridge emulation (multi relay/light) (EMUL_NONE, EMUL_WEMO or EMUL_HUE)

// -- Time - Up to three NTP servers in your region
#define NTP_SERVER1            ""       // [NtpServer1] Select first NTP server by name or IP address (
#define NTP_SERVER2            ""    // [NtpServer2] Select second NTP server by name or IP address (
#define NTP_SERVER3            ""  // [NtpServer3] Select third NTP server by name or IP address (

// -- Time - Start Daylight Saving Time and timezone offset from UTC in minutes
#define TIME_DST_HEMISPHERE    North              // [TimeDst] Hemisphere (0 or North, 1 or South)
#define TIME_DST_WEEK          Last               // Week of month (0 or Last, 1 or First, 2 or Second, 3 or Third, 4 or Fourth)
#define TIME_DST_DAY           Sun                // Day of week (1 or Sun, 2 or Mon, 3 or Tue, 4 or Wed, 5 or Thu, 6 or Fri, 7 or Sat)
#define TIME_DST_MONTH         Mar                // Month (1 or Jan, 2 or Feb, 3 or Mar, 4 or Apr, 5 or May, 6 or Jun, 7 or Jul, 8 or Aug, 9 or Sep, 10 or Oct, 11 or Nov, 12 or Dec)
#define TIME_DST_HOUR          2                  // Hour (0 to 23)
#define TIME_DST_OFFSET        +120               // Offset from UTC in minutes (-780 to +780)

// -- Time - Start Standard Time and timezone offset from UTC in minutes
#define TIME_STD_HEMISPHERE    North              // [TimeStd] Hemisphere (0 or North, 1 or South)
#define TIME_STD_WEEK          Last               // Week of month (0 or Last, 1 or First, 2 or Second, 3 or Third, 4 or Fourth)
#define TIME_STD_DAY           Sun                // Day of week (1 or Sun, 2 or Mon, 3 or Tue, 4 or Wed, 5 or Thu, 6 or Fri, 7 or Sat)
#define TIME_STD_MONTH         Oct                // Month (1 or Jan, 2 or Feb, 3 or Mar, 4 or Apr, 5 or May, 6 or Jun, 7 or Jul, 8 or Aug, 9 or Sep, 10 or Oct, 11 or Nov, 12 or Dec)
#define TIME_STD_HOUR          3                  // Hour (0 to 23)
#define TIME_STD_OFFSET        +60                // Offset from UTC in minutes (-780 to +780)

// -- Location ------------------------------------
#define LATITUDE               48.858360         // [Latitude] Your location to be used with sunrise and sunset
#define LONGITUDE              2.294442          // [Longitude] Your location to be used with sunrise and sunset

// -- Application ---------------------------------
#define APP_TIMEZONE           1                 // [Timezone] +1 hour (Amsterdam) (-13 .. 14 = hours from UTC, 99 = use TIME_DST/TIME_STD)
#define APP_LEDSTATE           LED_POWER         // [LedState] Function of led
#define APP_PULSETIME          0                 // [PulseTime] Time in 0.1 Sec to turn off power for relay 1 (0 = disabled)
#define APP_POWERON_STATE      POWER_ALL_SAVED   // [PowerOnState] Power On Relay state
#define APP_BLINKTIME          10                // [BlinkTime] Time in 0.1 Sec to blink/toggle power for relay 1
#define APP_BLINKCOUNT         10                // [BlinkCount] Number of blinks (0 = 32000)
#define APP_SLEEP              0                 // [Sleep] Sleep time to lower energy consumption (0 = Off, 1 - 250 mSec)

#define KEY_DEBOUNCE_TIME      50                // [ButtonDebounce] Number of mSeconds button press debounce time
#define KEY_HOLD_TIME          40                // [SetOption32] Number of 0.1 seconds to hold Button or external Pushbutton before sending HOLD message
#define SWITCH_DEBOUNCE_TIME   50                // [SwitchDebounce] Number of mSeconds switch press debounce time
#define WS2812_LEDS            6                // [Pixels] Number of WS2812 LEDs to start with (max is 512)

#define TEMP_CONVERSION        0                 // [SetOption8] Return temperature in (0 = Celsius or 1 = Fahrenheit)
#define TEMP_RESOLUTION        1                 // [TempRes] Maximum number of decimals (0 - 3) showing sensor Temperature
#define HUMIDITY_RESOLUTION    1                 // [HumRes] Maximum number of decimals (0 - 3) showing sensor Humidity
#define PRESSURE_RESOLUTION    1                 // [PressRes] Maximum number of decimals (0 - 3) showing sensor Pressure
#define ENERGY_RESOLUTION      3                 // [EnergyRes] Maximum number of decimals (0 - 5) showing energy usage in kWh

 * - Enable a feature by removing both // in front of it
 * - Disable a feature by preceding it with //

// -- Localization --------------------------------
  // If non selected the default en-GB will be used
//#define MY_LANGUAGE            bg-BG           // Bulgarian in Bulgaria
//#define MY_LANGUAGE            cs-CZ           // Czech in Czech
#define MY_LANGUAGE            de-DE           // German in Germany
//#define MY_LANGUAGE            el-GR           // Greek in Greece
//#define MY_LANGUAGE            en-GB           // English in Great Britain. Enabled by Default
//#define MY_LANGUAGE            es-AR           // Spanish in Argentina
//#define MY_LANGUAGE            fr-FR           // French in France
//#define MY_LANGUAGE            hu-HU           // Hungarian in Hungary
//#define MY_LANGUAGE            it-IT           // Italian in Italy
//#define MY_LANGUAGE            nl-NL           // Dutch in the Netherlands
//#define MY_LANGUAGE            pl-PL           // Polish in Poland
//#define MY_LANGUAGE            pt-BR           // Portuguese in Brazil
//#define MY_LANGUAGE            pt-PT           // Portuguese in Portugal
//#define MY_LANGUAGE            ru-RU           // Russian in Russia
//#define MY_LANGUAGE            tr-TR           // Turkish in Turkey
//#define MY_LANGUAGE            uk-UK           // Ukrainian in Ukrain
//#define MY_LANGUAGE            zh-CN           // Chinese (Simplified) in China
//#define MY_LANGUAGE            zh-TW           // Chinese (Traditional) in Taiwan

// -- Wifi Config tools ---------------------------
//#define USE_WPS                                  // Add support for WPS as initial wifi configuration tool (+33k code, 1k mem (5k mem with core v2.4.2+))
//#define USE_SMARTCONFIG                          // Add support for Wifi SmartConfig as initial wifi configuration tool (+23k code, +0.6k mem)

// -- OTA -----------------------------------------
#define USE_ARDUINO_OTA                          // Add optional support for Arduino OTA (+13k code)

 * Select ONE of possible three MQTT library types below
  // Default MQTT driver for both non-TLS and TLS connections. Blocks network if MQTT server is unavailable.
#define MQTT_LIBRARY_TYPE      MQTT_PUBSUBCLIENT   // Use PubSubClient library
  // Alternative MQTT driver does not block network when MQTT server is unavailable. No TLS support
//#define MQTT_LIBRARY_TYPE      MQTT_TASMOTAMQTT    // Use TasmotaMqtt library (+4k4 code, +4k mem) - non-TLS only
  // Alternative MQTT driver does not block network when MQTT server is unavailable. No TLS support
//#define MQTT_LIBRARY_TYPE      MQTT_ESPMQTTARDUINO // Use (patched) esp-mqtt-arduino library (+4k8 code, +4k mem) - non-TLS only

// -- MQTT ----------------------------------------
#define MQTT_TELE_RETAIN     0                   // Tele messages may send retain flag (0 = off, 1 = on)

// -- MQTT - Domoticz -----------------------------
//#define USE_DOMOTICZ                             // Enable Domoticz (+6k code, +0.3k mem)
  #define DOMOTICZ_IN_TOPIC    "domoticz/in"     // Domoticz Input Topic
  #define DOMOTICZ_OUT_TOPIC   "domoticz/out"    // Domoticz Output Topic

// -- MQTT - Home Assistant Discovery -------------
//#define USE_HOME_ASSISTANT                       // Enable Home Assistant Discovery Support (+2k code)
  #define HOME_ASSISTANT_DISCOVERY_PREFIX "homeassistant"  // Home Assistant discovery prefix

// -- MQTT - TLS ----------------------------------
  // !!! TLS uses a LOT OF MEMORY so be careful to enable other options at the same time !!!
//#define USE_MQTT_TLS                             // Use TLS for MQTT connection (+53k code, +15k mem)

// -- KNX IP Protocol -----------------------------
//#define USE_KNX                                  // Enable KNX IP Protocol Support (+9.4k code, +3k7 mem)
//  #define USE_KNX_WEB_MENU                       // Enable KNX WEB MENU (+8.3k code, +144 mem)

// -- HTTP ----------------------------------------
#define USE_WEBSERVER                            // Enable web server and Wifi Manager (+66k code, +8k mem)
  #define WEB_PORT             80                // Web server Port for User and Admin mode
  #define WEB_USERNAME         "admin"           // Web server Admin mode user name
  #define USE_EMULATION                          // Enable Belkin WeMo and Hue Bridge emulation for Alexa (+16k code, +2k mem)

// -- mDNS ----------------------------------------
#define USE_DISCOVERY                            // Enable mDNS for the following services (+8k code, +0.3k mem)
  #define WEBSERVER_ADVERTISE                    // Provide access to webserver by name .local/
  #define MQTT_HOST_DISCOVERY                    // Find MQTT host server (overrides MQTT_HOST if found)

// -- Time ----------------------------------------
#define USE_TIMERS                               // Add support for up to 16 timers (+2k2 code)
  #define USE_TIMERS_WEB                         // Add timer webpage support (+4k5 code)
  #define USE_SUNRISE                            // Add support for Sunrise and sunset tools (+16k)

// -- Rules ---------------------------------------
#define USE_RULES                                // Add support for rules (+4k4 code)

// -- Internal Analog input -----------------------
//#define USE_ADC_VCC                              // Display Vcc in Power status. Disable for use as Analog input on selected devices

// -- One wire sensors ----------------------------
                                                 // WARNING: Select none for default one DS18B20 sensor or enable one of the following two options for multiple sensors
//#define USE_DS18x20                              // Optional for more than one DS18x20 sensors with id sort, single scan and read retry (+1k3 code)
//#define USE_DS18x20_LEGACY                       // Optional for more than one DS18x20 sensors with dynamic scan using library OneWire (+1k5 code)

// -- I2C sensors ---------------------------------
#define USE_I2C                                  // I2C using library wire (+10k code, 0k2 mem, 124 iram)

#ifdef USE_I2C
//  #define USE_SHT                                // Enable SHT1X sensor (+1k4 code)
//  #define USE_HTU                                // Enable HTU21/SI7013/SI7020/SI7021 sensor (I2C address 0x40) (+1k5 code)
    #define USE_BMP                                // Enable BMP085/BMP180/BMP280/BME280 sensor (I2C address 0x76 or 0x77) (+4k code)
//  #define USE_BME680                           // Enable support for BME680 sensor using Bosch BME680 library (+4k code)
//  #define USE_BH1750                             // Enable BH1750 sensor (I2C address 0x23 or 0x5C) (+0k5 code)
//  #define USE_VEML6070                           // Enable VEML6070 sensor (I2C addresses 0x38 and 0x39) (+0k5 code)
//  #define USE_ADS1115                            // Enable ADS1115 16 bit A/D converter (I2C address 0x48, 0x49, 0x4A or 0x4B) based on Adafruit ADS1x15 library (no library needed) (+0k7 code)
//  #define USE_ADS1115_I2CDEV                     // Enable ADS1115 16 bit A/D converter (I2C address 0x48, 0x49, 0x4A or 0x4B) using library i2cdevlib-Core and i2cdevlib-ADS1115 (+2k code)
//  #define USE_INA219                             // Enable INA219 (I2C address 0x40, 0x41 0x44 or 0x45) Low voltage and current sensor (+1k code)
//  #define USE_SHT3X                              // Enable SHT3x (I2C address 0x44 or 0x45) or SHTC3 (I2C address 0x70) sensor (+0k7 code)
//  #define USE_TSL2561                            // Enable TSL2561 sensor (I2C address 0x29, 0x39 or 0x49) using library Joba_Tsl2561 (+2k3 code)
//  #define USE_MGS                                // Enable Xadow and Grove Mutichannel Gas sensor using library Multichannel_Gas_Sensor (+10k code)
//  #define MGS_SENSOR_ADDR    0x04              // Default Mutichannel Gas sensor i2c address
//  #define USE_SGP30                              // Enable SGP30 sensor (I2C address 0x58) (+1k1 code)
//  #define USE_SI1145                             // Enable SI1145/46/47 sensor (I2C address 0x60) (+1k code)
//  #define USE_LM75AD                             // Enable LM75AD sensor (I2C addresses 0x48 - 0x4F) (+0k5 code)
//  #define USE_APDS9960                           // Enable APDS9960 Proximity Sensor (I2C address 0x39). Disables SHT and VEML6070 (+4k7 code)
//  #define USE_MCP230xx                           // Enable MCP23008/MCP23017 for GP INPUT ONLY (I2C addresses 0x20 - 0x27) providing command Sensor29 for configuration (+4k7 code)
//    #define USE_MCP230xx_OUTPUT                  // Enable MCP23008/MCP23017 OUTPUT support through sensor29 commands (+1k5 code)
//    #define USE_MCP230xx_DISPLAYOUTPUT           // Enable MCP23008/MCP23017 to display state of OUTPUT pins on Web UI (+0k2 code)
  #define USE_MPR121                             // Enable MPR121 controller (I2C addresses 0x5A, 0x5B, 0x5C and 0x5D) in input mode for touch buttons (+1k3 code)
//  #define USE_CCS811                             // Enable CCS811 sensor (I2C address 0x5A) (+2k2 code)
//  #define USE_MPU6050                            // Enable MPU6050 sensor (I2C address 0x68 AD0 low or 0x69 AD0 high) (+2k6 code)
#endif  // USE_I2C

// -- SPI sensors ---------------------------------
//#define USE_SPI                                  // SPI using library TasmotaTFT

#ifdef USE_SPI

#endif  // USE_SPI

// -- Serial sensors ------------------------------
#define USE_MHZ19                                // Add support for MH-Z19 CO2 sensor (+2k code)
#define USE_SENSEAIR                             // Add support for SenseAir K30, K70 and S8 CO2 sensor (+2k3 code)
  #define CO2_LOW              800               // Below this CO2 value show green light (needs PWM or WS2812 RG(B) led and enable with SetOption18 1)
  #define CO2_HIGH             1200              // Above this CO2 value show red light (needs PWM or WS2812 RG(B) led and enable with SetOption18 1)
#define USE_PMS5003                              // Add support for PMS5003 and PMS7003 particle concentration sensor (+1k3 code)
#define USE_NOVA_SDS                             // Add support for SDS011 and SDS021 particle concentration sensor (+0k7 code)
#define USE_PZEM004T                             // Add support for PZEM004T Energy monitor (+2k code)
#define USE_SERIAL_BRIDGE                        // Add support for software Serial Bridge (+0k8 code)
//#define USE_SDM120                               // Add support for Eastron SDM120-Modbus energy meter (+1k7 code)
  #define SDM120_SPEED         9600              // SDM120-Modbus RS485 serial speed (default: 2400 baud)
//#define USE_SDM630                               // Add support for Eastron SDM630-Modbus energy meter (+2k code)
  #define SDM630_SPEED         9600              // SDM630-Modbus RS485 serial speed (default: 9600 baud)

// -- Low level interface devices -----------------
//#define USE_IR_REMOTE                            // Send IR remote commands using library IRremoteESP8266 and ArduinoJson (+4k code, 0k3 mem, 48 iram)
//  #define USE_IR_HVAC                            // Support for HVAC system using IR (+2k code)
//  #define USE_IR_RECEIVE                         // Support for IR receiver (+5k5 code, 264 iram)

#define USE_WS2812                               // WS2812 Led string using library NeoPixelBus (+5k code, +1k mem, 232 iram) - Disable by //
  #define USE_WS2812_CTYPE     NEO_GRB           // WS2812 Color type (NEO_RGB, NEO_GRB, NEO_BRG, NEO_RBG, NEO_RGBW, NEO_GRBW)
//  #define USE_WS2812_DMA                         // DMA supports only GPIO03 (= Serial RXD) (+1k mem). When USE_WS2812_DMA is enabled expect Exceptions on Pow

//#define USE_ARILUX_RF                            // Add support for Arilux RF remote controller (+0k8 code, 252 iram (non 2.3.0))

//#define USE_SR04                                 // Add support for HC-SR04 ultrasonic devices (+1k code)

//#define USE_TM1638                               // Add support for TM1638 switches copying Switch1 .. Switch8 (+1k code)

#define USE_RF_FLASH                             // Add support for flashing the EFM8BB1 chip on the Sonoff RF Bridge. C2CK must be connected to GPIO4, C2D to GPIO5 on the PCB (+3k code)

 * Debug features are only supported in development branch

//#define USE_DEBUG_DRIVER                         // Use xdrv_99_debug.ino providing commands CpuChk, CfgXor, CfgDump, CfgPeek and CfgPoke

 * Optional firmware configurations
 * Select none or just one for optional features and sensors as configured in sonoff_post.h
 * See for selected features

//#define USE_CLASSIC                              // Create sonoff-classic with initial configuration tools WPS, SmartConfig and WifiManager
//#define USE_SENSORS                              // Create sonoff-sensors with useful sensors enabled
//#define USE_KNX_NO_EMULATION                     // Create sonoff-knx with KNX but without Emulation
//#define BE_MINIMAL                               // Create sonoff-minimal as intermediate firmware for OTA-MAGIC

 * No user configurable items below

#if defined(USE_MQTT_TLS) && defined(USE_WEBSERVER)
  #error "Select either USE_MQTT_TLS or USE_WEBSERVER as there is just not enough memory to play with"

#endif  // _USER_CONFIG_H_

Configure Tasmota firmware

After you have transferred the Tasmota firmware to the socket, you still have to configure it correctly. Open the configuration website by entering the IP address of the connected socket in your browser address bar. How to find out the IP address is described in the article Displaying / finding the IP address of the devices in the network.


If you have opened the configuration website, you have to click on “Settings” to get to the configuration menu.
There you click on “Configure device”.
Now you can select in the category “device type” the setting “Sonoff S2X”. “Sonoff S2X” is the setting that would also work for the predecessor of the “Sonoff S26”, the “Sonoff S20”. That’s why there is “S2X” and not directly “S26”.
If you have selected the correct setting, you must now click on “Save” and the settings will be accepted and saved.

Remove programming connections

If you have transferred the Tasmota firmware to the control board, you can remove the connection cables again.

The connection lines are too long and too bulky to be stowed in the housing of the socket.
Desolder the leads by heating the solder pads again briefly. Make sure again that there are no connections between the solder pads.
Close-up of the solder pads after the connection leads have been removed.

Build the housing together again

Then you can reassemble the housing of the Sonoff S26 and plug it into a power outlet for testing. The socket should then log into your Wi-Fi and be available soon in the network.

I hope everything worked as described. If not or you have any other questions or suggestions, please let me know in the comments. Also, ideas for new projects are always welcome. 🙂


P.S. Many of these projects - especially the hardware projects - cost a lot of time and money. Of course I do this because I enjoy it, but if you appreciate it that I share these information with you, I would be happy about a small donation to the coffee box. 🙂

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