This module uses a previous project that used an Arduino the control the Plantower PMS5003 particle air quality sensor. The Arduino and the level converters have been removed and the TTL serial signals are fed back to the Raspberry Pi 4 in the main enclosure. The +5V sensor power supply provides the +5V supply to the sensor. The digital I/O signals from the sensor use the +3.3V levels which are compatible with the Raspberry Pi 4.
The PMS5003 uses laser scattering to determine the effective particle diameter and number of particles in each size bin. To ensure that it is sampling the surrounding atmosphere, the unit sucks air into the measurement chamber using a fan.
Communication to and from the PMS5003 using serial TTL. There is also a set control pin that puts the device onto a working or sleeping mode. A Reset pin is also provided that can reset the device.
When the device is working, it can operate in a passive or active mode. The passive mode requires that the host computer (Raspberry Pi) sends a command to make a reading. This is the appropriate mode if the readings are to be triggered at a particular interval.
The active mode automatically sends readings to the host without any prompting. If the rate of measurement change is low, the device sends a reading about every 2 seconds, but as the rate of change increases, the message rate increases, eventually rising to every 200ms.
The SET line which controls whether the sensor is active or sleep and the RESET line which resets the device are connected to the IO_MODULE. The Tx and Rx communication lines are connected to the Raspberry Pi's serial port.
The physical construction consists of placing the PMS5003 in a weather proof enclosure while allowing free air ventilation. There are two options available:
(1) Use one of the commercial radiation shields to hold the sensor. The smaller radiation shields will require the sensor to be held vertically, while it can be located horizontally in the larger radiation shield; or
(2) Held in a customer box to provide the shielding and ventilation similar to that provided by one of the radiation shields.