This is a work-in-progress project I started about a year ago. I started off designing an ECG circuit. The circuit features a battery charger, two preamp circuits connected to a 12-bit ADC. My goal was to stream ECG data through a bluetooth modem to a PC, so there is no on-board memory.
The MCU is the C8051F990 by Silicon Labs. I have found this chip to be amazing. It has a 12-bit ADC along with many other peripherals, and it comes in a tiny QFN package. The AD8293 amplifiers are fixed-gain precision amps, so the voltage measurements are very precise.
After I built a couple of the circuits, I found them really useful to have around as a precision multimeter. I use the circuit every day as a pH meter for my hydroponics system. The pH measurement streams to my android smartphone via Bluetooth Terminal.
This Processing sketch receives the serial data from the HC-05 Bluetooth modem, and graphs it in real time.
The MCU performs 10-bit measurements at a rate of 50ksps, and averages the result to obtain a 12-bit value. The PC receives a data point once every two milliseconds, which provides plenty of x-axis resolution.
After 12 hours of programming, and excessive amounts of coffee, I think the data shows a heart arrhythmia.