Chillout with The Relaxino Heart Beat Application.
A beta project for Arduino and Android developers / hackers. Requires Arduino development board, bluetooth module, Arduino code and a Grove heart beat sensor (or similar).
Please see for all details and project write up. You will need to follow instructions on my website. You can leave comments and ask questions on that site too. All the source code is freely available on my website [Gampa Geek].
Requires Bluetooth and API level 5 to 17 (Eclair to Jellybean)
It works by measuring your heart rate and taking an average over 20 beats. An LED on Arduino pin 13 flashes each time your heart beats, because each beat triggers an external interrupt. The average heart rate is sent by the Arduino every 20 beats over Bluetooth to the Android device.
You set a target rate on the Android, so a purple screen flashes when you are above target and a green one when you are at, or below the target heart rate. This allows you to try to relax and get feedback on how you are doing. Lie or sit down and try to relax, taking long deep breaths in and out, empty your mind and gently focus on the screen light (being in the dark helps so you can see the pulses through semi-closed eyelids).