ECG Lead Selector Switch circuit

lead selector ecg

Hi,
This is my first post and also this will be basic because my digital circuits skills have become useless in the years gone by. For reference: RA is right arm, LA is left arm, and RL is right leg.

I have built a simple 3 lead ECG circuit using an AD620 IC. The next step is to add a lead selector switch which closes 1 input and opens the other 2 (either RA, LA, or RL) and also closes all 3 with another option. To make it less complicated:

Position 1: RA closed, LA open, RL open
Position 2: LA closed, RA open, RL open
Position 3: RL closed, RA open, LA open
Position 4: All leads closed

From what I understand, this can be made by using a rotary wafer switch or dip switches but my concept is this:

I wish to create a digital circuit that controls which leads are open and closed (using a modular pushbutton switch) and the closed lead is displayed on two 7 segment display in numeric 01, 02, 03, 04 as RA, LA, RL, and All respectively. What would be even better is if the display showed alphabetic rA, LA, rL, and AL instead (lower case R because it looks like a capital A in a 7 segment display).

This circuit will be at the input of the AD620 sending the closed lead to the input and the open leads to ground.

I need a push out the door as to what components can be used to create the contraption I have described, if it is even possible. Any input is appreciated, even the complicated ones.

ecg lead switching

Dear Member

I am not an expert but it seems to me that you must look at the propability of using a micro controller.(PIC or something simular)
You want a push button to change the status and simultaneasiously it must show the status on a LCD screen.
A PIC 16F84 should beable to the job.

Regards

lead selector switch

does anyones have this circuit from this project?

proper attachment of ecg leads

Baboo,

The clinical connections of ECG wires are not single inputs to ground, but differential inputs between to two electrodes with reference (common) to RL as the "ground"

Attached is a page from Tektronix "Biophysical Measurements" by Peter Strong 1970. Though old (from my medical elecrtonics days), it 's still a decent reference.

This shows standard "LEADS" I, II, III, aVr, aVl, and aVf. Though not shown, the "common" on your differential amp is connected to the right leg, RL.

I have used OptoMosfet relays on the ADC input of micro controllers to select from several inputs. Like this: **broken link removed**. This can be configured as a SPDT switch. I have not tried them a 1mV ECG levels but it would be worth a try.

Ken