Posts in Arduino
Arduino Internet of Things Part 2: Lowering The Power Consumption Of The ATmega328P Breadboard Arduino And The HM-10 Bluetooth Module
Heat Transfer of the Raspberry Pi Using Arduino, An Infrared Thermometer, and Type-K Thermocouple
Arduino - Sending A String Over Bluetooth Using The HM-10

As an introduction to Bluetooth with Arduino or Raspberry Pi, I recommend using a component called the HM-10 [datasheet here]. The HM-10 is a Bluetooth low energy module that employ Bluetooth 4.0, which is currently the most widely used protocol for wireless devices (along with Wifi, but I will discuss this later). All of the current iPhones, Androids, and Google phones use Bluetooth 4.0, and it will likely be around for quite a while. The module is powered at 3.3V and consumes around 50mA (peak), 8.5mA (nominal), and can sleep with a current between 400uA - 1.5mA. It claims to have an open-space transmission range of 100m, and boasts transfer rates at 2 kilobytes per second. The underlying chip is a Texas Instruments CC-2540/2541 [see here]. The HM-10 is particularly germane because it cooperates nicely with the Arduino software with a mere four lines of code in the IDE. 

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A Heat Transfer Experiment with Coffee