In late 2011 and early 2012 we designed a four-channel airflow monitoring system for HVAC fans. The project includes modular air pressure sensors. Up to four pressure sensor modules can be connect to one display.
This project included two PCB designs, two PIC microcontroller firmware programs, and Windows PC software for building-specific configuration.
The main board is capable of outputting either 0-5V (voltage) or 4-20mA (current loop) to a separate HVAC control system or both simultaneously.
The current loop version is more complex and more expensive due to the electrical isolation requirement.
The back side of the main board is completely covered by a 4×20 character LCD display. Airflow can be displayed in either cfm (cubic feet per minute) or L/s (liters per second). The prototypes shown have pots to determine the necessary contrast setting for each model of display. Production units do not require any contrast adjustment.
The PC software is used to configure settings such as fan ID, fan factor (a number provided by fan manufacturers which is used to determine the cfm based on the air pressure differential on either side of the fan) and the range of each pressure sensor. The sensors can be calibrated to a variety of ranges so that a range can be selected for best results with a given model of fan.
Each airflow unit is tested with an automatic test fixture and reports PASS on its display or an error code indicating which channel failed which part of the test.
Over a thousand of these have been manufactured since 2012.