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6. Expansion Board
The User Interface Expansion Board included with the BGM121 Wireless STK includes the following features:
• 1x 3-axis accelerometer (Bosch Sensortech BMA280)
• 1x Joystick with 9 measurable positions
• 2x Push buttons and 2x LEDs
The connections between the Expansion Board and the BGM121 are shown in the figure below:
PA1 (GPIO)
BUTTON_LED2 (EXP7)
PD10 (GPIO)
BGM121
BUTTON_LED3 (EXP14)
Buttons
& LEDs
Accelerometer
BMA280
Analog
Joystick
JOYSTICK (EXP12)
ACC_MOSI (EXP4)
ACC_MISO (EXP6)
ACC_SCK (EXP8)
ACC_CS (EXP10)
ACC_INT (EXP9)
PA0 (ADC)
PC6 (US1_TX #11)
PC7 (US1_RX #11)
PC8 (US1_CLK #11)
PC9 (US1_CS #11)
PD11 (GPIO)
Figure 6.1. User Interface Expansion Board
The following sections contain more detailed information about each feature.
6.1 Accelerometer
Bosch Sensortec BMA280 is a triaxial, low-power, low-g accelerometer sensor with SPI interface. It features 14-bit digital resolution and
allows very low-noise measurement of acceleration in 3 perpendicular axes and can therefore sense tilt, motion, shock and vibration.
Please refer to Bosch Sensortec's product page for a detailed datasheet of this sensor:
http://www.bosch-sensortec.com/bst/products/
6.2 Push Buttons and LEDs
The Expansion Board contains two push buttons (marked
BTN2
and
BTN3
on the PCB) and two LEDs (LED2 and LED3, not marked
but placed correspondingly above the push button markings). One push button and one LED share the same I/O pin on the BGM121.
The push button is connected to the LED through a transistor, allowing the I/O to be used either as an input (for reading the push button
state) or as an output (to control the LED state on or off).
When configured as an input,
"0"
indicates that the button is being pressed and
"1"
that the push button is not being pressed. Likewise,
when configured as an output,
"0"
will turn the LED on and
"1"
will turn it off.
Pressing a push button will also light up the corresponding LED because the LED is controlled by the same line (state) regardless of
whether it is the BGM121 or the push button that pulls the line low.
The each button is debounced by an RC filter with a time constant of about 1 ms. Pressing the push button while having the pin config-
ured as an output in high state (
"1"
) will not cause damage, but will cause extra current to flow.
UG234: BGM121 Blue Gecko SiP Module Wireless Starter Kit User's Guide
Expansion Board
silabs.com
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