NRF51822

This is a Nordic Semiconductor system on chip with a 2.4 GHz radio and a Cortex-M0 processor.

The hardware Bluetooth baseband provides raw BLE packets in a frame buffer. Nordic provides the S110 softdevice which implements a Bluetooth Low Energy stack. It also supports the proprietary protocol spoken by nRF24L01+ and nRF24LE1.

Getting started

Nordic has evaluation and development kits available for $99. These are highly recommended for anyone who wants to work with nRF51822 because they give you access to the full datasheets, reference manual, SDKs and tools.

The development kits have two boards that are meant to plug into the nRFgo platform, as well as a small version of the Segger J-Link debugger that uses the standard ARM 10 pin 50 mil header. These boards are useful but a little difficult to power, unless you have the more expensive nRFgo board.

The evaluation kit is probably a better choice for most people. It includes a board with every GPIO broken out, a CR2032 holder, and an on-board debugger.

The standalone J-Link is a great debugger. There is a cheaper version for educational and non-commercial use.

Proximity tag

First blinking test KiCad files

This is a simple breakout board with an nRF51822 chip, Johanson integrated balun, chip antenna, the DC/DC converter to save battery life, two pushbuttons and two LEDs. Every analog pin is broken out, and all peripherals can be mapped to these pins. The S110 Bluetooth LE softdevice works well.

The board uses mostly 0603 components, and only a single 0402 that is in the RF path.

Power can be provided from a CR2032 holder on the bottom or through the pins. There is currently no reverse polarity protection.

Note that this board does not include a 32.768 kHz crystal, so you need to set up the Bluetooth stack to either use the internal RC oscillator or derive the low frequency clock from the 16 MHz high frequency clock. The Bluetooth stack has code to periodically recalibrate the RC oscillator from the high frequency clock. I would say the low frequency crystal is only worth it if you intend to have the tag on sleep for long periods.

The boards and stencil are from Smart-Prototyping.