Ecg Heart Rate Monitor Design

keane2097

I'm currently building a heart rate monitor based on the MSP430 from Texas Instruments. This is the schematic I'm basing my preamplifier design on, it's a TI design with some electrical isolation added:



I've built a test version of the circuit on breadboard and I want to check that I've done it properly without attaching it to myself...

Unfortunately I'm not sure what input signals I should apply to test it suitably.

Basically, can anyone tell me what kind of signal I should apply to the right-leg driven circuitry and to each of the inputs that will be connected to the patient's arms?

DublinDilbert

The signals are going to be very small ( a couple of mV at best)..... very hard to generate with a signal generator....

You front end should be battery powered, so there would be no safety issue connecting it to a person, and checking the output from the optical isolator... It does mean you'll need a beautiful assistant!!



You could also add in a digital opto isolator to turn on/off the battery power to the front end, when device doing the monitoring is powered up.... Means batterys won't go flat, a nice addition...

PS:- if your doing this as a project, you could look at the phase response of the front end on paper. You want a linear phase response, so your not deforming the waveform.... Something like besil filtering would be useful here...

keane2097

DublinDilbert wrote: »

The signals are going to be very small ( a couple of mV at best)..... very hard to generate with a signal generator....

You front end should be battery powered, so there would be no safety issue connecting it to a person, and checking the output from the optical isolator... It does mean you'll need a beautiful assistant!!

PS:- if your doing this as a project, you could look at the phase response of the front end on paper. You want a linear phase response, so your not deforming the waveform.... Something like besil filtering would be useful here...

This circuit is just to boost the small input voltage I'll be measuring from the patient while eliminating noise as much as possible, the signal will then be sampled and digital filtering and signal processing will be carried out using a microcontroller.

I should be able to generate a small enough voltage with the function generator I have alright. I'm thinking that a suitable type of input would be something like a 1mV sinusoid into one arm input and something like 1.5mV sinusoid into the other...

Any idea what signal I would put into the driven right-leg circuitry to test the Common Mode noise rejection?

Turbulent Bill

Slightly OT, but there was an article in the IEEE Spectrum a few months ago about the development of automatic defibrilators including the different waveforms used, some physiological details etc. I know you're building an ECG monitor but it might be useful for background info.

DublinDilbert

keane2097 wrote: »

Any idea what signal I would put into the driven right-leg circuitry to test the Common Mode noise rejection?

That is your grounding point in the circuit. So you would attach the ground lead from your signal generator onto this....

CathalMc

Once you have it working with the waveform generator, you should introduce an impedance network to model the impedance of the body. I would imagine these test setups would be described in similar design whitepapers to that which you are using for your circuit. ADI & TI are good sources for these.