Hardware Details

The board has two I2C buses. The Qwiic connectors and the SDA1/SCL1 pins reach only the ATtiny404, which answers at 0x30 to 0x37. The ATtiny404 runs the LMP91000 front end and the ADS1115 ADC on a second bus, SDA2/SCL2, where the LMP91000 sits at 0x48 and the ADS1115 at 0x49. A 2.5 V voltage reference sets the front end's reference voltage. The front end's analog output VOUT, the ADC's ALERT pin and its free inputs AIN1 to AIN3 are on the header for your own use.

Key specifications

Specification	Value
MCU
Bridge MCU	Microchip ATtiny404 (factory firmware)
Interface
Interface	I2C, analog, digital GPIO
Qwiic compatible	Yes, 2 connectors
Default I2C address	0x30
I2C address changeable	Yes, 0x30 to 0x37 with the ADDRESS switch
Breadboard compatible	No
Header pins	VOUT (analog out), ALERT, AIN1 to AIN3 (analog in)
Power
Supply voltage	3.3 V, no regulator; the Qwiic connectors share this supply
Logic level	3.3 V only
Other
Gas	Hydrogen sulphide (H2S)
Gas cell	SGX-4H2S-300, electrochemical
Measurement range	0 to 300 ppm H2S; max overload 500 ppm
Measurement accuracy	Repeatability < ±2% H2S equivalent; linearity < 2% (0 to 300 ppm); resolution < 0.1 ppm typical
Response time	T90 under 30 s
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
Dimensions	38 x 38 mm

Pinout

Soldered Electrochemical H2S Gas Sensor Breakout (Qwiic) pinout

Pin marking	Pin name	Description
3V3	Power	3.3 V supply in. On the top row and the side row, shared with both Qwiic connectors.
GND	Ground	Ground. On all three rows.
SDA1, SCL1	Qwiic I2C bus	The same bus as the Qwiic connectors, to the ATtiny404. 10 kΩ pull-ups to 3V3 (JP5).
SDA2, SCL2	On-board I2C bus	The bus between the ATtiny404, the LMP91000 and the ADS1115. 10 kΩ pull-ups to 3V3 (JP6).
VOUT	Analog output	The LMP91000 output voltage, which the ADS1115 also reads on its input AIN0.
ALERT	ADC alert	The ADS1115 ALERT/RDY output, with a 10 kΩ pull-up to 3V3. Also wired to the ATtiny404.
LMPEN	Front-end enable	The LMP91000 MENB pin, held low by a 10 kΩ resistor to GND. Also wired to the ATtiny404.
AIN1, AIN2, AIN3	Analog inputs	The ADS1115's other three inputs, free for your own analog signals.
UPDI	Programming	The ATtiny404 programming pin.

Voltage and logic levels

Connection	Supported voltage	Notes
3V3 pins and Qwiic connectors	3.3 V	There is no regulator: everything on the board runs from this supply.
SDA1, SCL1, SDA2, SCL2	3.3 V logic	Pulled up to 3V3 through 10 kΩ.

Power the board from 3.3 V only. It has no regulator, so the header and both Qwiic connectors feed the 3.3 V supply straight to the chips.

Dimensions

The board measures 38 x 38 mm and has four 3.2 mm mounting holes. The gas cell sits on the underside.

Jumpers

The ADDRESS switch and jumpers JP1 to JP6 on the top side

Jumper	Default	Function
ADDRESS switch (1 to 3)	Address 0x30	Sets the board's I2C address on the Qwiic bus, from 0x30 to 0x37.
JP1	Closed	Joins the front end's analog ground (AGND) to GND. Cut it to separate them.
JP2 to JP4	JP2 closed, JP3 and JP4 open	Set the ADS1115 address on the on-board bus: JP2 ties ADDR to 3V3 (0x49), JP3 ties it to SDA2 (0x4A), JP4 ties it to SCL2 (0x4B).
JP5	Closed	Connects the 10 kΩ pull-ups on SDA1 and SCL1 (the Qwiic bus). Cut it to disconnect them.
JP6	Closed	Connects the 10 kΩ pull-ups on SDA2 and SCL2 (the on-board bus). Cut it to disconnect them.

Close only one of JP2, JP3 and JP4. With JP2 closed, closing JP3 or JP4 ties SDA2 or SCL2 to 3V3, and closing JP3 and JP4 together ties SDA2 to SCL2. Either way the on-board bus stops working and the board cannot take readings.

When you use the board at 0x30 to 0x37, leave JP2 to JP4 as shipped: JP2 closed, JP3 and JP4 open. In that mode the Arduino library and the MicroPython module send the ATtiny404 only the ADC gain and data rate, never an ADS1115 address. To put several boards on the Qwiic bus at 0x30 to 0x37, use the ADDRESS switch.