On Sat, Jan 29, 2011 at 10:28 PM, Olin Lathrop w= rote: > V G wrote: > > I'm trying to understand how the right leg driver circuit is working. > > It's basically introducing a signal in the right leg to null out the comm= on > mode signal from the electrodes near the heart. This actively cancels > common mode noise before it gets into circuits where it could cause troub= le > and be perceived as differential signal, or cause other problems like > swamping the front end so that it becomes non-linear and introduces > manufactured noise signals or becomes deaf to the tiny differential signa= l. > > > 1. Why is it called the "right leg driver"? > > Most peoples hearts are on the left side. The right leg is therefore the > spot on the body farthest fron the heart and a signal there will be more > common mode than one introduces elsewhere. In practise, the left leg > probably works about as well. > Not quite right. It is not about the "distance" of reference point to the heart, it's about the impedance seen between the heart and the reference point. If you are talking about inhomogeneous and isotropic structures, using geometrical distance is like taking pi as 2 (not even 3). If it's EKG what you are trying to perform, closest surface to semimembranosus or right earlobe will do the same. --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .