Block Diagram

MCU
SAMD21G18A
External crystal:
32.768kHz
Ext. relay
connector
USB
USB cable
3.3V LDO
USB/
SWD
SWD
Testpads
(Programming)
I2C
LDR
(MAX44009)
SPI
Bluetooth
(nRF51822)
External crystals:
32.768kHz
16MHz
UART
LTEM
(SARA-R412M)
Internal crystal:
19.2MHz
3.8V LDO
RGB
LED
LEDs
(WS2812B)