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i must do an ECG MONITOR with 2 palm sensor ground free

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vincengineer

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palm sensor

Hi i'm Vincent and for an hobby i have to do the same ecg circuit that is built in more TAPIS ROULANT...

Any one can explane me in which material are made the palm sensor and what tipe of schematic can i use for free gound type circuit?

thank's

Vincent
 

rina_1220

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ecg monitor schematic

Has anyone got any hints on how to make an ecg monitor ground free?
 

Audioguru

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how to make a ecg monitor circuit

Without a ground then it will probably pickup a lot of mains hum.

Go to the moon or out in the middle of a desert where there is no mains hum.

EDIT:
They are not grounded. The circuit has a "common ground" attached to one leg. Is that the "ground" that you don't want?
 

rina_1220

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ecg with two electrodes

I have seen some commercial products which work without the ground.
They are small devices with two electrodes, one for each thumb, and they work fine.
 

rina_1220

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ina114 ecg

yes. I don't want the "common ground" electrode.
 

kender

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ecg schematic oscilloscope

I know that 2-electrode EKG (without common ground) can be done. One of my friends knows the details. I'll ask him.

In the meantime, I'd like to invite your question to a group dedicated to sensors: http://tech.groups.yahoo.com/group/sensorforum. You might get some good answers there.
 

FvM

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remove noise from ecg soldering

It's basically a matter of expectable common mode voltages. For a portable, battery operated device, where no or only small common mode interferences must be feared, even a single ended amplifier input may be sufficient. Using a differential amplifier without ground reference, the input impedance must be low enough to prevent common mode overload. A simple principle rather than a special circuit.
 

rina_1220

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ground free ecg amplifier

I have my circuit made with an INA114
When I had its basic assembly like the datasheet, with capacitors connected to pin 7 and 4 and common ground, I had very big noise when I disconnected the 3rd wire. Now I removed these capacitors and I don't get that noise, but I still can't see the signal in good conditions.
I'm improving my filters here to see what happens.
 

rockywjj

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palm ecg monitor

Hi, rina_1220
You ever copied the book “Design of Pulse Oximeters” into a pdf file.

In EdaBoard, you provid:
https://www.edaboard.com/viewtopic.php?t=325704&highlight=
h**p://www.4shared.com/file/60586623/7df141d6/Design_of_Pulse_Oximeters.html”
Unfortunately, but I could visit them.

Would you please send the PDF file to me directly?
My email address is rockywjj@gmail.com
Thank you very much!

Rocky
 

rina_1220

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where do the sensors go for the ecg

Well, I am still working on it. And I have got the signal seen on the image when I test the circuit with an ecg simulator. If I remove the 3rd electrode from the simulator (which is supposed to be the LL electrode), I get a little noise, but nothing that would spoil my signal.
The only thing is that this circuit just won't work if I test it with a real person. I have tried 2 different attempts, which are: 1. copper plates soldered to wires and attached to the body; and 2. real commercial electrodes soldered to wires and attached to the skin.
The other side of the wires, of course, go connected to the amplifier exactly the same way as if they were connected to the simulator.
What I see on the oscilloscope screen is just nothing but a small noise (small amplitude) and no signal.

I have a commercial electrocardiograph here and the simulator is usually used with it normally. So I don't think it would be a matter of difference of amplitude between the simulator and the real signal. Or, could it be? Also, I have tried setting up the gain when using it with real people, but no success.

What could be wrong?
Any help would be appreciated.
 

FvM

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ina114 dc

You most likely have a problem with INA114 input bias, cause you didn't follow the data sheet recommendations in this respect. But without knowing your circuit, this can't be judged. You absolutely need a DC path from differential inputs to supply midpoint respectively ground for a bipolar supply, e. g. trough resistors. You'll find it in the datasheet for any isolated source (= without ground connection). Did you establish it?
 

rina_1220

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ina114 isolator

My circuit is as follows. G1, for INA 114 is no more than 10. And because it's supplied with batteries, I haven't seen any difference while using or not a filter between the 2 OPs I have there. I have tried with and without some filter in between btw. I have tried with a low pass 100hz filter also, but no difference.
 

Audioguru

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ecg sensor circuit

Here is a document about an ECG circuit.
Here is the schematic of an ECG circuit that filters then feeds the common-mode low frequencies and DC to the left leg as a reference.
 

rina_1220

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circuit of an ecg sensor

Yep, it is possible to attach more than one file per message. I am going to read it and take a look at the schematic you sent me.
Thanks.
 

FvM

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coupling capacitor ina114

I must take Audiogurus part now and post a LM741 comment first. It's not just lousy, it's specified for minimum supply voltage of +/- 5V. Input common mode range and output voltage swing at +/- 3V supply are near to zero and may be none, at worst case. Thus, there is no guarantee for the second stage to operate at all. Considering some offset voltage from the electrodes and the missing high pass, this may be a sufficient reason for the circuit to fail. Another reason may be common mode overload by interfering voltages.

Two electrode monitors are typically used for simple portable applications. This implies, that you don't connect a mains operated desktop oscilloscope, that introduces interfering voltages just by grounding the circuit. But I'm only guessing. Basically, the reason for failure can be found by tracing the signal with an oscilloscope, provided, you understand INA114 specification and behaviour.

Cause the problem may be related to DC input voltage, you can try a capacitive coupling (several uF non-electrolytic capacitors) of the inputs.
 

rina_1220

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gnd free ecg

Then, shouldn't it fail with either a real person or a simulator??
Because it works with my ecg simulator but not with me.
By the way, I have assembled the circuit on this page (http://www.stm32circle.com/projects/project.php?id=31) today and I get the same thing: it works with the simulator but not when I try on a real person.

I am now pretty sure I am doing something really wrong about the electrodes. I just don't know what. :|
 

Audioguru

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how to ground an ecg monitor

The simulator didn't read about and didn't learn about the very high common-mode voltages on real people.

You need to isolate the circuit from the ground of your pc or oscilloscope. Use an opto-isolator.
 

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