What is it?

This is a small (18 mm x 33 mm) development board for Nordic's nRF51822 SoC with Cortex M0 processor and Bluetooth LE 2.4 GHz radio. Also on board are Bosch’s BMP280 pressure sensor and Invensense’s MPU9250 9 DoF motion sensor, a MAX1555 LiPo battery charger with USB connector (charging only), and a MIC5528 LDO 500 mA 3V3 regulator. There is LED indication for 3V3 on, battery charging, and a GPIO-controlled rgb LED. There are side through-holes for 3V3 and GND, I2C (GPIO 0, 1), UART (GPIO 9, 11), the SWD program port, and 12 GPIOs (2, 3, 4, 8, 10, 12, 14, 15, 16, 25, 28, 29).

The nRF51822 ARM Cortex M0 processor runs at 16 MHz which provides moderate computational power for managing sensors, leds, and other peripheral devices. It is fast enough to perform open-source Madgwick sensor fusion on the MPU9250 motion sensor data at 300 Hz. The nRF51822 also has an embedded 2.4 GHz radio and uses a softdevice to support the BlueTooth Low Energy protocol. This means the pressure and motion sensor data can be streamed wirelessly to a smartphone or server so you can measure the user's movement and environment without disturbing the action!

The twelve GPIOs can be configured dynamically in software to serve as additional UART, SPI, I2C, I2S, PWM or any other peripheral function through the use of the embedded multiplexer inside the nRF51822 chip. GPIO pins 2, 3, and 4 have analog pin and ADC function capability; the rest are standard digital IO pins. Consult the nRF51822 product specification for all the peripherals supported.

Why did you make it?

I have been making a variety of devices using the nRF51822 and I needed a basic platform to try out new ideas, connect different sensors, and just serve as a convenient prototyping platform for this wonderfully useful chip.

This breakout board has many of the functions most people will need for an Internet of Things (IoT) development platform including some environmental awareness (pressure, temperature sensors), orientation and motion tracking (accelerometer, gyroscope, and magnetometer), and since most IoT applications are small and battery powered, I included an on-board LiPo battery charger with a mini-B USB connector to make recharging easy. The breakout has a convenient on-off switch that conserves battery power when the device is not in use. Lastly, I made the board small; it has just enough GPIOs broken out to the edges to be useful but is still small enough to fit into a pocket or be attached to a hand or leg. Where can it fit? Use your imagination...

What makes it special?

Even though the nRF51822 development board is Teensy-sized, the nRF51822 is not as easy to program as the Teensy. The easiest way if you are not familiar with using a full-fledged tool chain like Keil or Crossworks is to use mbed.

I use the RedBearLabs BLE Nano Kit programmer; just connect programmer 3V3, GND, DIO and DCLK to the breakout board 3V3, GND, DIO, and CLK pins and you can drag and drop the compiled mbed HEX file right into the Nano programmer's hard drive folder and the development board nRF51822 will be programmed. Very easy. The hard part (for me) is setting up the BLE, but there is an online forum at mbed and the Nordic Developer's Forum to help. I used a Pally BLE scanner app and measured a strong -50 dbm signal with my iPhone a foot away from the nRF51 board. I used the battery level/temperature sensor mbed demo and measured a simulated change in battery level from more than forty feet away. So this ceramic chip antenna and standard antenna matching circuit is performing as expected for a 2.4 GHz radio.

I have written a basic program to get MPU9250 (and BMP280) data and perform sensor fusion on it using this board. There are many examples and tutorials on the mbed site on how to write C programs and how to set up the BLE protocol. This basic program is not a full software solution but should allow most people to get started with their own software development using this board and the mbed compiler.

The nRF51822 is a BLE engine so it can transmit the BMP280 and MPU9250 sensor data (or data from any other sensors you add) wirelessly to a server or iPhone. This package is small but powerful enough to prototype your IoT idea and get it out there!

Order the pc board from OSH Park and assemble your own or buy the fully assembled and tested board from me and start making your IoT idea a reality!