Hello,

I am building an ECG simulator using an ESP8266 and a DAC. The idea is that the ECG wave is uploaded from the PC to ESP and through the DAC the ECG signal is generated in a 12-bit resolution.
So far so good but my goal is to simulate at least 4 leads of the ECG (RL, LL, RA, LA). During my search I saw some projects using resistors to connect the leads to a common signal, or having one lead generating the waveform and the rest to the ground. but so far no explanation why.

Does anyone know the reason why?
or knows a relation between the ECG leads that can be achieved through circuit? (or at least through some extra code in the ESP?)

Thanks!
CK

 

The explanation is neither quick nor simple. If you want to simulate an ECG, it will help to do some background reading on what an ECG is as well as the general idea of a biopotential. Please understand that I am not an electrophysiologist, so take this as just my non-SME opinion.

Consider that there are bipolar and unipolar leads in a standard 12 lead ECG. In this case, a “lead” is referring to a voltage between two points and not to a single strand of wire.

Unipolar leads have a single reference point (usually the electrode on the right leg [call it a reference GND for the moment]). Bipolar leads reference a potential between an electrode and one or more electrodes that are not that reference ground.

The standard 12 lead ECG has only 10 electrodes but it is called a “12 lead” because there are 12 “views” which, together, do a very good job of creating a picture of cardiac function.

I would suggest that you go through some tutorials (like the ones linked below) before you get into schematics.

https://courses.kcumb.edu/physio/ecg primer/ecgleads.htm

https://www.cablesandsensors.com/pages/12-lead-ecg-placement-guide-with-illustrations

http://www.cvphysiology.com/Arrhythmias/A013

I’m not sure exactly what you mean by “using resistors to connect the leads to a common signal”. Sometimes protective resistors are used on electrodes for safety (e.g., the Rp here https://www.dovepress.com/a-simple-...maker-pul-peer-reviewed-fulltext-article-MDER). If you can show me a particular schematic, I *might* be able to help, but again, I would suggest basic tutorials before particular schematics.

Hope this helps.