This is an ECG device that I planned, designed, soldered and programmed. Currently it is very simple, using an ADS1298 analog frontend and a STM32F103 microprocessor to send the data via USB to a host computer, where a Python script can then plot the data.
Below is a sample of what this device can record. Pretty much professional medical quality!
It lacks some bells and whistles like automatic lead of detection, pacing and respiratory rate detection and does not conform to IEC 60601, so it can't be used in a clinical setting. It does however have rudimentary ESD protection and input resistors to prevent death in case of an electrical fault where 230 volts AC touch the device. Of course the power is supplied by a 5 volt USB cable, so that shouldn't happen anyway!
Here is a picture of the PCB layout.
