Currently the following sensors are supported by specific firmware here, however others could be added later on.
⬛ CO2e Sensor: CCS811
This digital sensor is embedded on the CJMCU-8118 circuit board and powered by a custom driver that uses the sensors I²C protocol.
The CCS811 measures the CO2e ("CO2 equivalent") value of the surrounding air in particles per million (ppm). This value also incorporates the levels of methane (CH4), nitrous dioxide (N2O) and other synthetic gases, besides the regular CO2 measurement, which makes up about 75% of the CO2e. This value is therefore used by environmental scientists nowadays to give more accurate measurements about the current levels of emissions in the air.
As emissions vary depending on the air's temperature and humidity, the CCS811 sensor has inbuilt temperature and moisture sensors. It uses those to offset the variation of the measuring conditions to the optimal lab conditions. Please give the sensor a minute after startup to fully calibrate. However, it is important to notice that the sensor has a lower limit of 400ppm CO2e that can be detected.
🟦 Oxygen Sensor: AO-03
The analog AO-03 sensor measures the O2 content of the surrounding air in percent (%). It is embedded in a custom circuit board that is amplifying the measured voltage, because the changes in oxygen levels are usually just very slight and therefore the changes in voltage are also only minimal. Please give the sensor a minute after startup to fully calibrate. This AO-03 circuit board is designed as described below and depicted in the following:
🟨 Light Intensity Sensor: GL5528
A light sensitive photo-resistor is used to measure the luminous intensity of the surrounding light waves in lumen per square meter (lux). The resistance of this sensor is measured within a voltage divider circuit with a second resistor of 10k Ohm, inbuilt in the KY-018 circuit board. This value can then easily be transformed into the actual light intensity. Be aware that the luminous intensity is rising exponentially fast with increasing brightness levels of the environment.
🟩 Temperature Sensor: LM35
This analog thermometer can measure temperatures between −55°C and 150°C. It guarantees an accuracy of +/- 1°C over the whole range.
The sensors are linked to the PSLab with reverse polarity protected connectors, to enable the user to exchange sensors, without the need of unsoldering the jumper cables directly from the PSLab. In particular, qwiic connectors were used for the I²C sensors, as well as regular 3 pin connectors for the analogue sensors.
The connecting cables are color coded as follows:
| Voltage | Ground | Signal | SDA | SCL | |
|---|---|---|---|---|---|
| qwiic | red | black | blue | yellow | |
| 3 pin to sensor | red | brown | yellow | ||
| 3 pin to board | red | black | brown |
Those connectors are then attached to the sensors by about 50cm long cables, making it for example possible to use the sensor in a climate chamber, while keeping the box itself outside of it.
In order to make the sensors as water and temperature resistant as possible, their PCBs are covered with conformal coating and all pin connections are enclosed in, mostly glue coated, shrink tubing.