Leads in EKG-shield

[kbs]

Hi,
being a novice in arduino programming, but wtih a medical background, I apologize if my questions might have obvious answers. I have browsed through the forum, but have not found hese questions being raised before.
Setting up my one EKG shield with Olimex328 and the strap on electrodes, running the demo software, I get nice clean readings in elecguru and Brainbay, provided I ensure good skin contact and limit movement. It seems like the only lead read is lead I 
(reference: https://upload.wikimedia.org/wikipedia/commons/thumb/1/19/Limb_leads_of_EKG.png/1024px-Limb_leads_of_EKG.png )
Trying to get 3 leads, I would not hesitate to obtain another two shields, but my concern is the management of cables, as each new shield would require another two electrodes, meaning 3 electrodes on each hand (am I right, or did I get this wrong?).

A normal 3 lead ECG usually requires 3 electrodes, as lead II and lead III is calculated from the very same three electrodes as lead I. Is it possible to switch between the three leads with the EKG shield through software or are there technical limitations? Seems like the readings are done, but not processed? If three shields are necessary to get three leads, could the three electrodes still be used for all three shields, or is another load of cables required? Are there any other arduino sketches available for ECG on the EKG-shield?

[LubOlimex]

Hey,

The electrodes are the same for any extra shields, however, you don't need to place all the feedback electrodes! If you have more than one SHIELD-EKG-EMG you can connect only one DRL electrode. For the extra shields just connect the + and - that form one channel.

Note that you would need to set the AIN_SEL jumpers for each board to a different position.

All readings are processed. The hardware and the software code are suitable for up to 6 channels (6 shields). The hardware is limited by the AIN_SEL jumpers. For the software limits check the TXBuf[] array. By default you don't need to adjust anything in the software code - all available data would be processed.

Best regards,
Lub/OLIMEX

[kbs]

Hi, and thanks for the reply!

Fiddeling with the device (one shield only), I cannot see that the DRL really serves a purpose, it makes no/little difference to the reading whether it is on or off. With the three electrodes connected, you would theoretically be able to read three leads. My thought would be to split this signal in three (with different polarities) and feed it to three shields to make three leads from three electrodes, in stead of placing seven electrodes to do the same thing. Would this be feasible without too much interference from the other shields (they read serially and not parallell (?), but maybe too close in time?). The cables seem fairly poorly shielded, but if feasible, would this splitter require any shielding?