Digital Holter with PIC ?!

[Eugeniu]

HI !
I wish to do for personal use a Holter (something like this ) to can record my heart puls . Is not necesary to record an electrical puls on many channels . Is enough to can record a sound from my heart on a single channal . But , is necesary to can record 24 hours , to see records on display , and sort it after frequency , amplitude .
Any ideas will be usefully !

Thank you !

[Jerson]

Do-able. However, I am sure you need to sample at least 10 times in a second to accomodate upto 180beats/minute. You will need something like FRAM to store the data. My rough estimate is around 1M octet of storage for storing 24Hrs to be able to reproduce the waveform later.

[Eugeniu]

Do-able. ..............................My rough estimate is around 1M octet of storage for storing 24Hrs to be able to reproduce the waveform later.

This time , 24Hrs , is used in Hospital , I think that will be usefully for me , one or two hrs. To can start when is necesary and stop when isn't .

[Jerson]

My knowledge of Holter is limited to the days when they used to record ECG on audio tape. Even in this type, if I recall correctly, there used to be 2 channels min. 1 ch used to be the ECG, other was a control signal when the wearer would signal discomfort by pressing a button. Usually, Holter is worn for 24 Hours till you return it to the health care institute

[BrianT]

Go to the Texas Instruments site and have a look at their Medical Applications Guide. There are also plenty of ECG front ends on the web if you can't find the TI pages. You can simplify the front end to just an instrumentation amplifier and an opamp. You need a three electrode ECG system to reduce 50/60 Hz interference and movement artifacts. The signal input electrodes go to left chest and right chest and the common mode (anti-interference) output signal goes to the right ankle - perhaps the belly in a mobile system.

The ECG signal is 10 microvolts to a few millivolts so you need a sensitive amplifier, preferably with an inbuilt notch filter to kill the mains interference.

My ECG recorders turn on every ten minutes and record a ten second 'tape recording' of the animals heart data plus environmental data. The PQRS signal is pretty fast so the sampling rate must be about 200 samples per second or you will miss the heart beat. Once you have got stable 'tape recordings' you can then set about devising an algorithm to extract heart rate or interbeat variability or whatever you are looking for and save just a two byte number rather than a 2048 byte block.

Because the input signal is so low, you cannot have any other systems running during the signal capture phase or the local interference will overwhelm your results. I store the data as a 2048 byte block in the PIC 18F4620 internal RAM and then write the data as 8 x 256 byte blocks out to the external flash. I am using multiple M25P64 memory chips.

In summary, you can make a holter recorder with an analog front end and a PIC processor.

HTH
Brian

[Eugeniu]

Thank you Brian for your usefully informations . I have find " Medical Applications Guide " from TI . I am reading it . I understand that your ECG is self- makeing , is it ?

> In summary, you can make a holter recorder with an analog front end and a PIC processor.

This is so imprtant ! I'll try to do it .(with some / more help)

[Eugeniu]

Thank you Brian for your usefully informations . I have find " Medical Applications Guide " from TI . I am reading it . I understand that your ECG is self- makeing , is it ?

> In summary, you can make a holter recorder with an analog front end and a PIC processor.

This is so imprtant ! I'll try to do it .(with some / more help)

Apologize me for this double email (it's my browser problem )