Ozone 3 Click as its foundation uses the 3SP-O3-20 (110-407), a high-performance ultra-thin electrochemical gas sensor that can sense ozone concentration up to 20ppm from SPEC Sensors. An electrochemical sensor like this one generates a current proportional to the volumetric fraction of the gas. This current is converted and transformed into the voltage by the analog front-end (AFE), so it can be sampled by the MCU or converted with the external A/D converting circuit.

The sensor has very high sensitivity and short response time; however, the longer it is exposed to a particular gas, the more accurate data it can provide, especially true when calibration is performed. It is advised to protect the sensor when used in critical applications. In ideal conditions, the lifetime of this sensor is indefinite, but in real-life applications, the expected working life is more than five years (10 years at 23 ± 3 ˚C; 40 ± 10 %RH).

Ozone 3 Click communicates with the MCU through the I2C serial interface using the LMP91000, a configurable AFE IC for low-power chemical sensing applications from Texas Instruments that generates the output voltage proportional the sensor current. The voltage between the referent electrode (RE) and the working electrode (WE) of the 110-407 is held constant, with the bias set by the variable bias circuitry. This type of sensor performs best when a fixed bias voltage is applied. Also, this Click board™ has two additional ICs onboard. The first one is the MCP3221, a 12-bit successive approximation register A/D converter from Microchip, and the second is the OPA344, a single supply, rail to rail operational amplifier from Texas Instruments.

The RST pin of the mikroBUS™ socket, routed to the MEMB pin of the LMP91000, represents the enable feature of the I2C interface. When it is driven to a LOW logic level, the I2C communication is enabled, and the host MCU can issue a START condition. Note that the RST pin should stay at a LOW state during the communication.

Besides that, it is possible to use an onboard switch labeled as AN SEL to select the IC to which the VOUT pin from the LMP91000 AFE is routed. If the switch is in the position marked as ADC, the VOUT pin will be routed to the input of the MCP3221 ADC. This allows the voltage at the VOUT pin to be read via the I2C interface as digital information. When the switch is in the AN position, the VOUT pin of the LMP91000 is routed to the input of the OPA344. The output of the OPA344 Op-Amp has a stable unity gain, acting as a buffer so that the host MCU can sample the voltage at the VOUT pin of the AFE via the AN pin of the mikroBUS™ socket.

This Click board™ can operate with both 3.3V and 5V logic voltage levels selected via the VCC SEL jumper. This way, it is allowed for both 3.3V and 5V capable MCUs to properly use the I2C communication lines. However, the Click board™ comes equipped with a library containing easy-to-use functions and an example code that can be used, as a reference, for further development