*Note this version updates version 2017-001-015 with slightly smaller SWD programming header holes for POGO PIN programming. Please use 015 if you plan to solder in a 2x5 header per the BOM.
This is a LEGO Minifigure sized development board using an Atmel SAMD21E 32-Bit ARM chip. I basically followed the recommended layout/setup from the SAMD21 spec sheets.
Included on Mini SAM is a WS2812B LED pad connected to PIN 27, a 0603 LED connected to PIN 15, a reset button with support components per the datasheet, and a generic button that is active HIGH on PIN 28. The 0603 LED is connected in series with a 1Kohm resistor, part of R1, and care should be taken when selecting an 0603 LED such that at a supply of 3.3V, no more than 5mA is required.
Programming port is a standard10-pin SWD for ARM based processors, which is a 2x5 1.27mm pitch connector. The SWD line is pulled up with a 1Kohm resistor, part of R1. In the BOM, either purchase the 2x5 straight pin connector OR the 2x5 POGO connector and do not populate board.
The SDA/SCL pins are pulled high with 4.7KOhm resistors, R2, per SDA/SCL recommendations.
The voltage regulator is an AP2112K-3.3V which is rated at 600mA at 3.3V. Plenty of current for the SAMD21E and a few other accessories such as the WS2812B.
This version has SMT layout for two single row 2.54mm pitch headers on the back. It is designed to be protoboard friendly and when populated the headers are the same width as a DIL package (7.62mm or .3") and span the center of a protoboard.
PINs 27 and 28 are not connected to headers - due to lack of space - but instead have two pads near the bottom of the board. PIN 27 is connected to the on-board WS2812B. PIN 28 is connected to the on-board BUTTON.
The Analog Reference (PIN AREF) - has a pair of decoupling/filtering capacitors.
The micro-USB connector has an RC filter between the case/shield of the connector and GND. If R6 and C13 are left un-populated the case/shield is an open circuit - which is the next best option. Also included is space for a PRTR5V0U2X ESD protection circuit on USB Data lines. This may also be left un-populated and USB will function normally.
I have put together a sample BOM via Mouser.com which I’m including here. It can be used as a reference. Optional, but highly recommended components: SW2812B 3535 LED, 0603 LED, SW2 (BUTTON), R4, R5, R6, C13, and PRTR5V0U2X. R1 is for the 0603 LED and SWCLK - If not populating the 0603 LED this may be left un-populated as well and programming via SWD should still work as I’ve seen other boards without the 1Kohm resistor on SWCLK. R2 is the 4.7Kohm pull-up resistor pair for SDA/SCL. Many breakout boards using chips that run off SDA/SCL typically come with the 4.7Kohm pull-up resistor pair included - as such it may not be needed on Mini SAM - but it is included for ease of future components. Please review the schematic for additional details and be aware that the BOM on Mouser.com may be out of date. The SW2812B is not in the Mouser BOM - due to lack of parts.
I would suggest not purchasing the 2.54mm pitch SMT male headers from Mouser, as you can find this much cheaper elsewhere. The best I could find on Mouser is (2) 5-Pin and (2) 6-Pin headers. Mini SAM requires (2) 11-PIN headers. I suggest buying breakaway headers in 25-50 PIN lengths.
Arduino FIRMWARE/BOOTLOADER is complete, but I’m still testing all functions. So far all PINs work in digital setup and all analog PINs work accordingly. ANALOG and special function pins (MOSI, SDA, SCK, etc) can be accessed in Arduino by their name.
Please check my Github for the latest design files and bootloade/firmware.
More details can be found on Github