Arduino library for the Nordic nRF8001 Bluetooth Low Energy chip
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README.md

nRF8001 support for Arduino

This is a work in progress. Most of the functionality of the nRF8001 chip is implemented, but not all commands and interactions have been fully tested.

Installation

On a Mac:

cd ~/Documents/Arduino/libraries
git clone https://github.com/guanix/arduino-nrf8001.git nRF8001

The included example works with the Heart Rate function of the Nordic iOS app and sends the nRF8001’s internal temperature reading as heart rate and the fixed number 78 as battery level. It assumes the following pin assignments, easily changed:

  • RESET on digital pin 7
  • REQN on digital pin 9
  • RDYN on digital pin 8

This library uses the AVR chip’s hardware SPI support, so the SCK (CLK), MISO and MOSI pins cannot be changed:

  • MOSI on digital pin 11
  • MISO on digital pin 12
  • SCK on digital pin 13

Remember that nRF8001 expects 3.3V supply and logic levels. Connecting it to a typical Arduino will fry it. You must either use a level shifter/buffer, or a 3.3V Arduino, or a clone such as Seeeduino that can switch between 3.3V and 5V modes.

Technical Overview

nRF8001 is a slave-only Bluetooth Low Energy (Bluetooth 4.0) transceiver. It requires an external antenna and matching components, but little else. At least one vendor markets a complete module incorporating the antenna, which only requires a decoupling cap and a ground plane.

Communication with the nRF8001 uses a custom binary SPI protocol that is documented in the datasheet. Communication is full duplex and happens in transactions where the master can send a request while the slave simultaneously sends a response or event.

In addition to the typical SS pin to send a command (called REQN here), there is an additional pin, RDYN. When the master wants to initiate a transaction:

  1. Master brings REQN low.
  2. Slave (nRF8001) brings RDYN low.
  3. SPI transaction proceeds. Master sends a command and simultaneously receives a message (an event or a response to a previous command.)

When the slave initiates a transaction:

  1. Slave brings RDYN low.
  2. Master brings REQN low.
  3. SPI transaction proceeds.

Because nRF8001 SPI transactions are asynchronous, while the Arduino nRF8001 library contains a number of functions to send commands to the nRF8001, those functions almost never immediately return a response. Instead, you must register handlers, special functions that you define, which will in turn be called when the response (or an event) is received. A typical simple Arduino sketch that uses nRF8001 will use global variables to coordinate between handlers and the main event loop.

This library is not interrupt driven. Responses from the nRF8001 may be received whenever you send a command, but if you are not ready to send a command immediately, you must call nRF8001::poll() (or its variant with a timeout) to poll for responses or events.

In order to define services, you must use Nordic’s nRFgo Studio software. The software will generate a services.h file that you must place in the library’s folder inside your Arduino installation’s libraries folder. The software will define a number of pipes. The included services.h is Nordic’s heart rate monitor example, which allows the slave to send heart rate information on pipe 5 and battery level information on pipe 8. The exact format of the data messages are defined in the relevant service specification.

The heart rate example

The included heart rate example defines two event handlers, temperatureHandler for receiving temperature from the nRF8001’s built-in thermometer and stores it in a global variable, and the catch-all eventHandler, which only calls nRF8001::debugEvent, a function that prints extensive information about received events to the serial port. It works with Nordic’s test app on iPhone 4S, iPhone 5 and the third generation iPad.

After initializing the nRF8001 class, registering handlers and calling nRF8001::setup to send setup messages from services.h to the nRF8001 chip, it then calls nRF8001::getDeviceAddress() to get the device address and nRF8001::getTemperature() to request the temperature. It then calls nRF8001::connect to wait for a connection from a peer device.

In the loop, we continuously poll with nRF8001::poll using a 2-second timeout, and every 2 seconds or so, we read a new temperature and send that out as a heart rate. If the connection is disconnected, we call nRF8001::connect again to wait for a new connection.

License

Copyright © 2012 Guan Yang

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.