Integration¶
This section provide a top level aspect on how to integrate the W-BACnet module into a product.
Overview¶
Presented below is an over head block diagram of components required for integration of the module. The module itself needs to be soldered on to a carrier board.
Block diagram of a W-BACnet module
In order to fully integrate the module into a product the carrier board needs to provide the following interfaces:
- RS485 - for external connection between other BACnet devices and the module. For an example see Reference design for RS485 circuit.
- SPI or UART management interfaces - for communication with the W-BACnet device, and to configure its RS485 communication parameters. The product designer can choose any of the options, they have the same capabilities.
- Push button - press while powering up the device to put it into DFU/bootloader-mode. It is also possible to pull the bootloader/button pin high to 3.3 V while powering on the device. However, it is also possible to enter this mode using the SPI or UART management interfaces (without having to manually power on or off the device).
A complete integration also requires:
- Power - see Power supply recommendations and Reference design for power supply for further information.
- Antenna - An external antenna is required, see Antenna guideline for more information.
Power supply recommendations¶
The W-BACnet Module is designed for 3.3 V operation. Do not apply power to any of the pins until the 3.3 V rail is connected.
To ensure reliable operation, the supply pin should be decoupled with a 100 nF ceramic capacitor close to the supply pin. It is also recommended to add a high value ceramic bulk capacitor, such as 47 uF, which will reduce the current ripple of the 3.3 V net.
During radio transmission, current consumption will rise sharply to 150 mA typical, 250 mA max. A typical slew rate value is 300 A/s during radio transmission.
| Symbol | Parameter | Min. | Typ. | Max. | Unit |
|---|---|---|---|---|---|
| VDD | Supply voltage | 3.0 | 3.3 | 3.6 | V |
| Vrise | Supply rise time (0 V to 3.7 V) | 60 | ms | ||
| IDD | Supply peak current capability | 150 | 250 | mA | |
| IDD_rate | Supply current slew rate | 300 | A/s |
Common mistakes¶
The integration of the W-BACnet module is a relatively simple process, but for optimal RF performance it is important to follow the power supply and layout considerations. Failure to do so may result in inferior RF performance. Some important highlights to avoid the most common mistakes are shown below:
- The carrier PCB shall be of the recommended type and have a proper ground plane
- Product enclosure and carrier PCB shall adhere to the clearance recommendations
- Product enclosure shall not block radio-signals
- Power supply pins shall have sufficient decoupling
- All ground pins shall be available on the carrier PCB
- Programming pins (P20 and P21) shall be accessed