reel board


reel board [1] is a evaluation board based on the Nordic Semiconductor nRF52840 SoC. The board was developed by PHYTEC Messtechnik GmbH in cooperation with Zephyr Project for the Hackathon - “Get Connected”. The board has a built-in debug adapter based on the DAPLink interface firmware and NXP MK20DX128VFM5 SoC.

It is equipped with the Electrophoretic (electronic ink) Display (EPD), environmental (temperature, humidity, light, accelerometer) sensors, and Bluetooth connectivity making it easy to experiment and evaluate the Zephyr OS in these kinds of use cases:

  • battery powered sensor node
  • low-power, low-cost human-machine interface (HMI) for remote control and environmental sensor monitoring
  • temperature and humidity monitor on your table
  • product, name or price tag
  • interactive badge for meetings and conferences

The board provides support for the Nordic Semiconductor nRF52840 ARM® Cortex®-M4F SoC with an integrated 2.4 GHz transceiver supporting Bluetooth® Low Energy and IEEE® 802.15.4.

The schematic can be found on the reel board website [1].


On the front of the board are RGB-LED, ADPS9960 and HDC1010 sensors, and Electrophoretic Display. The RGB-LED is controlled by the nRF52840 via GPIO pins. Display is controlled by the nRF52840 via SPI and 3 GPIOs.

On the back side of the board are all other components such as nRF52840, a circuit for the Debug Adapter, On/Off and power source switch, battery holder, buttons and the MMA8652FC (accelerometer) sensor.

ADPS9960 is a Digital Proximity, Ambient Light, RGB and Gesture sensor. HDC1010 is a digital humidity and temperature sensor. MMA8652FC is a 12-bit Digital Accelerometer. All sensors are connected to the I2C bus and one GPIO pin each, which can be used as an interrupt source.

reel board front

reel board front (Credit: PHYTEC)

reel board back

reel board back (Credit: PHYTEC)

Since PCB version 1507.2, the nRF52840 SoC is not soldered directly to the board but integrated as a module on a NOTM.2 adapter. The wiring is identical for versions 1507.1 and 1507.2.


GDEH0213B1 is the display with which the board was introduced in 2018. Unfortunately, this display has been discontinued. Currently the board is delivered with the display GDEH0213B72. It is expected that the display will be replaced over time due the short product lifecycle of this type of displays. The following table lists the displays used on the reel board. The label on the ribbon cable can help to distinguish the displays. According to the display type, the correct designation must be used for building an application.

Display Ribbon Cable Label Controller / Driver Board Designation
Good Display GDEH0213B1 HINK-E0213 SSD1673 / ssd16xx reel_board
Good Display GDEH0213B72 HINK-E0213A22 IL3897 / ssd16xx reel_board_v2

Power supply

The board is optimized for low power applications and supports two power source configurations, battery and micro USB connector.

The On/Off switch can choose which power source is used.

reel board uses a TPS610981 boost converter to generate supply voltage for nRF52840 and peripherals (sensors and EPD). The boost converter has two modes:

  • Active mode - supply voltages for nRF52840 and peripherals are on
  • Low Power mode - only supply voltage for nRF52840 is on

The mode is controlled by MODE pin (P1.00).


Actually there is no possibility to reduce energy consumption by the Low Power mode. Both voltages are always on, see: boards/arm/reel_board/board.c

Supported Features

The reel_board board configuration supports the following hardware features:

Interface Controller Driver/Component
NVIC on-chip nested vectored interrupt controller
RTC on-chip system clock
UART on-chip serial port
I2C on-chip i2c
PWM on-chip pwm
SPI on-chip spi
GPIO on-chip gpio
FLASH on-chip flash
RADIO on-chip Bluetooth
SENSOR off-chip MMA8652FC polling: ADPS9960 polling: HDC1010 polling

Other hardware features are not supported by the Zephyr kernel.

Connections and IOs

Port P0

Name Function Usage
P0.00 XL1 32.768 kHz oscillator
P0.01 XL2 32.768 kHz oscillator
P0.02 expansion connector pin 30 None
P0.03 expansion connector pin 31 None
P0.04 expansion connector pin 19 None
P0.05 expansion connector pin 11 None
P0.06 UART0_TX UART Console over USB
P0.07 Button user button (S5)
P0.08 UART0_RX UART Console over USB
P0.09 expansion connector pin 27 None
P0.10 expansion connector pin 29 None
P0.11 RGB LED (red) GPIO
P0.12 RGB LED (green) GPIO
P0.13 PWM LED | Buzzer GPIO
P0.14 EPD Busy output GPIO
P0.15 EPD Reset input GPIO
P0.16 EPD DC input GPIO
P0.18 CPU Reset Reset (S4)
P0.21 SPI3_MISO SPI (not connected)
P0.22 HDC1010 DRDYn GPIO
P0.26 I2C_0 I2C
P0.27 I2C_0 I2C
P0.28 expansion connector pin 3 None
P0.29 expansion connector pin 52 None
P0.30 expansion connector pin 1 None
P0.31 expansion connector pin 37 None

Port P1

Name Function Usage
P1.00 peripheral power on GPIO
P1.01 expansion connector pin 32 None
P1.02 expansion connector pin 34 None
P1.03 expansion connector pin 17 None
P1.04 expansion connector pin 15 None
P1.05 expansion connector pin 13 None
P1.06 expansion connector pin 33 None
P1.07 expansion connector pin 35 None
P1.08 expansion connector pin 45 None
P1.09 RGB LED (blue) GPIO
P1.10 expansion connector pin 47 None
P1.11 expansion connector pin 49 None
P1.12 expansion connector pin 51 None
P1.13 expansion connector pin 36 None
P1.14 expansion connector pin 48 None
P1.15 expansion connector pin 50 None

Solder Jumper and Testpoints

There are several labeled solder jumpers on the board. These can be used to connect a logic analyzer to check the behavior of a driver or to measure the voltage of a signal.

reel board Jumper and Testpoints

reel board testpoints (Credit: PHYTEC)

I2C bus and sensors testpoints

Name Type Usage
J19 closed solder jumper testpoint I2C SDA
J20 closed solder jumper testpoint I2C SCL
J7 closed solder jumper testpoint INT1 MMA8652FC
J24 closed solder jumper testpoint INT2 MMA8652FC
J11 closed solder jumper testpoint INT APDS9960
J12 closed solder jumper testpoint DRDYn HDC1010

EPD testpoints

Name Type Usage
J13 closed solder jumper testpoint EPD Busy
J14 closed solder jumper testpoint EPD Reset
J15 closed solder jumper testpoint EPD DC
J16 closed solder jumper testpoint EPD SPI_CS
J17 closed solder jumper testpoint EPD SPI_CLK
J18 closed solder jumper testpoint EPD SPI_MOSI

Power supply testpoint

Name Type Usage
J21 closed solder jumper testpoint peripheral voltage on/off
TP11 testpoint testpoint peripheral voltage
TP12 testpoint testpoint nRF52840 supply voltage VDD_nRF
TP13 testpoint testpoint boost converter input voltage

Build-in Debug Adapter

The debug adapter is based on the DAPLink interface firmware and NXP MK20DX128VFM5 SoC. The adapter is powered via a micro USB connector and is always on when the board is connected to the USB host. reel board can be flashed and debugged, powered either from battery or USB. If the Adapter is powered via USB, the Adapter circuit heats the board slightly and the temperature sensor can output values up to 1.5 degrees higher.

reel board Debug Adapter

reel board Debug Adapter overview (Credit: PHYTEC)

Debug Adapter Firmware

DAPLink firmware for the adapter can be found at DAPLink reel board Firmware [2]. To update the firmware (if necessary), the adapter must be started in bootloader mode. For this, the board should be disconnected from the USB host, the J22 should be closed (use tweezers for this) and the board reconnected to the USB host.

Debug Adapter Jumper

Name Type Usage
J3 open solder jumper close to pass UART TX to external adapter
J4 open solder jumper close to pass UART RX to external adapter
J22 open solder jumper close to start adapter in bootloader mode

Adapter LEDs

Name Type Usage
D11 green flashes when adapter is active
D14 red reserved
D15 yellow reserved

Expansion Connector

The expansion connector has the same dimensions and similar pinout as the BBC MicroBit edge connector. The expansion components that are designed especially for the reel board are called link boards.

reel board Expansion Connector

reel board Expansion Connector (Credit: PHYTEC)

Programming and Debugging

Applications for the reel_board board configuration can be built and flashed in the usual way (see Building an Application and Run an Application for more details).


If you use Linux, create a udev rule (as root) to fix a permission issue when not using root for flashing.

# echo 'ATTR{idProduct}=="0204", ATTR{idVendor}=="0d28", MODE="0666", GROUP="plugdev"' > /etc/udev/rules.d/50-cmsis-dap.rules

Reload the rules and replug the device.

$ sudo udevadm control --reload-rules

Finally, unplug and plug the board again for the rules to take effect.

Build and flash applications as usual (see Building an Application and Run an Application for more details).

Here is an example for the Hello World application.

First, run your favorite terminal program to listen for output.

$ minicom -D <tty_device> -b 115200

Replace <tty_device> with the port where the reel board can be found. For example, under Linux, /dev/ttyACM0.

Then build and flash the application in the usual way.

# From the root of the zephyr repository
west build -b reel_board samples/hello_world
west flash


Please use reel_board_v2 to build a application for the board equipped with the GDEH0213B72, see Display.

# From the root of the zephyr repository
west build -b reel_board_v2 samples/hello_world
west flash


You can debug an application in the usual way. Here is an example for the Hello World application.

# From the root of the zephyr repository
west build -b reel_board samples/hello_world
west debug

Testing the LEDs and buttons

There are 2 samples that allow you to test that the buttons (switches) and LEDs on the board are working properly with Zephyr:

You can build and flash the examples to make sure Zephyr is running correctly on your board.