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Heart Rate Ring . Wei Dong Dec 16, 20 08. Objective. Known problems of existing products (relatively expensive, bulky, not open, etc.) To create a ring that can change its color according to heart rate (friendly user interface, less expensive, small package )
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Heart Rate Ring Wei Dong Dec 16, 2008
Objective • Known problems of existing products (relatively expensive, bulky, not open, etc.) • To create a ring that can change its color according to heart rate(friendly user interface, less expensive, small package) • Opera of the Future (open hard/software, access to raw data, multi communication interfaces)
System Architecture Hardware: heart rate sensor (LED-photodiode, op-amp, etc.), A/D and MCU (Arduino), I2C-Controlled RGB LED (BlinkM) Software: A/D conversion, BPM counter, LED driver
Heart Rate Sensor • Principle • Circuit schematic
Heart Rate Sensor (cont’d …) • Sensor outputs • Sensor demo
Software (ATmega 168 firmware) • A/D conversion // Module description: measures output with the range of 0-5000mV, 10 bits convertor scale 2^10 // Functions called: analogRead(), Serial.print() • Heart Rate // Module description: // (1) averages the output over every 5 milli-seconds, // (2) triggered on rising-edge of signal, then measures amount of milli-seconds before next rising-edge, // (3) converts the measured heartbeat from milliseconds to beats-per-minute: 60000/beat-interval // Functions called: millis() • BlinkM LED driver // Module description: // (1) finds RGB/HSB (hue, saturation, brightness) in the look-up table according to heart rate // (2) sends color code via I2C // Functions called: BlinkM_funcs.h (ref.), Wire.send(), and I2C functions
Lessons Learned • Easy to know but difficult to act (知易行难): tuning for multi-amp circuit, system integration, etc. • Chooses the one suitable for your application: starting from middle (中庸之道) • Adopt right materials and mechanical designs
Future works • Chooses better ring design and material • Finalizes the circuit to ring package with SMD components