Soldered Electrochemical H2S Gas Sensor Breakout (Qwiic)

This board measures hydrogen sulphide (H2S) with an SGX-4H2S-300 electrochemical cell. The LMP91000 analog front end biases the cell and turns its current into a voltage, a 16-bit ADS1115 ADC converts that voltage, and an ATtiny404 talks to both chips for you, so your microcontroller sees a single I2C device.

The cell covers 0 to 300 ppm and reaches 90% of a step in under 30 s. It works from -30 to 50 °C and 15 to 90% RH. You set the front end over I2C and give the libraries the cell's sensitivity; they also include a zero calibration routine for clean air. The ADS1115's other three inputs, AIN1 to AIN3, are on a header for your own analog signals.

Connect the board with either of the two Qwiic connectors or the 2.54 mm headers. It runs from 3.3 V; there is no regulator, so the header and the Qwiic connectors share one 3.3 V supply. The default address is 0x30; the three DIP switches move it from 0x30 to 0x37, so up to eight boards share one bus. The front end's analog output VOUT and the ADC's ALERT pin are on the header too. There are libraries for Arduino and MicroPython, plus an ESP-IDF component and an ESPHome component.

• Gas: hydrogen sulphide (H2S)
• Gas cell: SGX-4H2S-300, electrochemical
• Range: 0 to 300 ppm
• Response time: T90 under 30 s
• Repeatability: < ±2% H2S equivalent
• Operating conditions: -30 to 50 °C, 15 to 90% RH
• Expected cell life: over 24 months in air
• Analog front end: Texas Instruments LMP91000
• ADC: Texas Instruments ADS1115, 16-bit
• Bridge MCU: Microchip ATtiny404 (factory firmware)
• Interface: I2C, address 0x30 (0x30 to 0x37 by switch)
• Supply: 3.3 V, no regulator; the Qwiic connectors share this supply
• Header pins: VOUT (analog out), ALERT, AIN1 to AIN3 (analog in)
• Connectors: 2x Qwiic, 2.54 mm headers
• Dimensions: 38 x 38 mm