Peter Balch has released a guide for building an electrocardiogram sensor with integrated display, powered by a low-cost Arduino Nano — and points out it may be of interest to those looking into the symptoms of COVID-19.
"You might be interested in your heart during the COVID-19 pandemic," Balch writes. "COVID-19 can sometimes give rise to cardiac complications including arrhythmia, ischaemia, infarction, tachycardia and conduction problems. But by the time that happens, you're probably lying in an intensive care ward."
"This ECG (Electrocardiogram) unit has an integrated display. The display can show individual heart beats in a large format, the train of heart beats in a small format and a Poincaré plot. It is battery powered and can be worn round your neck on a lanyard."
The heart of the device is an Analog Devices AD8232 electrocardiogram amplifier and conditioner, which Balch notes "takes a lot of the hard work out of designing a[n ECG] system." The AD8232 is connected to an Arduino Nano — "or Uno or Mini with a 16MHz [ATmega]328P," Balch adds - which drives a 2.8" ILI9341-based 320x240 SPI-connected display. "I chose a 320x240 SPI display," Balch writes, "because [it] can be updated reasonably quickly and uses few Arduino pins."
The finished project can be cycled through three display modes: a "large display" that offers fine detail for one or two detected heart beats; a "small display" which has less detail but allows a dozen or so heart beats to be seen on the screen at once; and a Poincaré display showing historical rhythm information.
"Some researchers think that HRV [heart rate variability], ectopic beats, and other irregularities in heart rate are best detected by a Poincaré display," Balch explains. "Although ECG Poincaré plots been around since 1990, they are not 'mainstream' and many workers prefer a simple chart."
The full guide write-up, and source code for the Arduino sketch, can be found over on Instructables.