Data Sheet

Bluegiga – A Silicon Labs Company 8
Design guidelines
Certain hardware related design guidelines should always be followed when developing applications based on
the BT121 module.
2.1 PCB layout recommendations
 All ground pads should be connected to a ground plane.
 The antenna layout should follow the example shown in Figure 2 below and avoid the designs shown
as crossed over.
 BT121 requires minimal free space around the module and only the white area marked in the PCB
picture series presented in Figure 2 below needs to be free of copper and components.
Figure 2 PCB layout recommendations for BT121 application boards
2.2 Power supply recommendations
The regulator used must be capable of supplying a peak current of 150 mA and the regulator must be of a
type stable with ceramic capacitors.
2.3 Software application related options
BT121 can be used either as a stand-alone solution by using the Bluegiga BGScript™ scripting language or
alternatively if the application software size or other factors require together with an external host processor by
using Bluegiga BGAPI™ commands. The decision on which approach to use is most often dictated by the
limits set by the internal memory of the BT121 module.
2.4 Firmware updating related recommendations
To enable firmware updating an external UART interface connection as shown in Figure 3 on the next page is
mandatory. BT121 firmware can be updated through the UART interface by holding the host MCU in reset
state which typically will free the UART lines to be used by the update interface.