52
votes
Can an oscilloscope be used as an EKG?
Absolutely, yes. But you'll need a frontend.
An EKG is usually just an instrumentation amplifier or a multistage amplifier with as many dB of common mode rejection as you can get.
The problem is that ...
- 29.3k
25
votes
Accepted
Why would you put your input amplifier in front of your filtering for an ECG signal?
Am I missing some important reason why you would do the signal
conditioning in this order?
Yes you are...
The front-end differential amplifier will be chosen such that it has a common-mode ...
- 473k
21
votes
Accepted
What does this op-amp circuit do? (part of an ECG)
The right leg driver tries to drive the average voltage of the body to cancel out noise. The right leg is chosen because it is far from the heart, so any signal injected on there will be common mode ...
- 315k
19
votes
Can an oscilloscope be used as an EKG?
You can find very simple integrated front-ends which perform the necessary signal conditioning. Just as an example: AD8232
Also available in boards:
Source: sparkfun
Another (harder) option would be ...
- 9,638
14
votes
What does this op-amp circuit do? (part of an ECG)
This circuit, and the need for it, make much more sense when you consider some things that aren't depicted. First, remember that is is necessary to establish some sort of reference voltage on the ...
- 30.6k
9
votes
Circuit for small level voltage detection (microvolts)
Although it is possible to design a Sallen Key filter with a gain higher than unity, this is rather uncommon for a reason. Any gain in it introduces positive feedback into the structure and leads it ...
- 8,546
9
votes
Why would you put your input amplifier in front of your filtering for an ECG signal?
Andy and Nick offered great answers. Let me try to beef them up just a little.
First, the math says that amplifying then filtering is equivalent to filtering then amplifying. This, of course, ...
- 30.6k
9
votes
Can an oscilloscope be used as an EKG?
An EKG machine does have a display not unlike an oscilloscope. That's clear enough.
But what an oscilloscope is missing is the detection and amplification circuitry that pick up the heart's ...
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8
votes
Circuit for small level voltage detection (microvolts)
The opamp in a Sallen-Key filter is supposed to be a unity-gain buffer. Yours has a gain of +3, so it isn't surprising that it's oscillating. Wikipedia talks about this.
If you need that much gain, ...
- 178k
8
votes
Why would you put your input amplifier in front of your filtering for an ECG signal?
I'll second @Andy's answer, and I'd like to add one thing.
A passive low-pass filter between the electrodes and the InAmp is called for. I put the cutoff frequency somewhere in the kHz region.
...
- 38.6k
7
votes
why is a GROUND electrode needed with a referential amplifier?
Differential amplifiers such as instrumentation amplifiers, with or without unity gain buffers, have a certain working range for the common-mode voltage.
In general they will stop working if either ...
7
votes
Why would you put your input amplifier in front of your filtering for an ECG signal?
The only filtering you ever do before the first amplifier is that related to shape of antenna/waveguide. And that only applies to microwave and higher frequencies.
Conventional passive filters add ...
- 3,010
7
votes
Accepted
Is it valid to use transistors to route signals through the circuit?
Unfortunately, bipolar junction transistors (BJT) won't work as you intended here.
I believe you are assuming that a BJT, when switched on, is like a very low resistance between collector and emitter, ...
- 47.3k
6
votes
Is it valid to use transistors to route signals through the circuit?
Can I use transistors to route/switch ECG signals?
Short answer: NO.
ECG signals are in the +/-0.5-1mV range, so too low for any transistor type circuit.
The schematic you show will not work under any ...
- 22k
5
votes
why is a GROUND electrode needed with a referential amplifier?
After looking at some schematics: (Google: "physiological amplifier circuit" and select Images tab), this is one example:
Many amplifiers do use A-R directly similar to instrumentation amplifiers. ...
- 81.4k
4
votes
Low-power Li-Ion Battery Charging
TP4056 is one of the cheapest solutions. Assembled avail online as below, $2cdn ~$1usd on sale with this data sheet . It uses the 3 stage charge standard method 1A-CC, CV , Shutdown @100mA cutoff (...
- 148k
4
votes
Can we have the action potential an AC current
Because of the nature of the cell membrane, which is permeable to some ions and impermeable to others, the cell is at a Nernst equilibrium, which is a chemical engineering concept in which electrical ...
- 30.6k
4
votes
Accepted
ECG circuit Pre amplifier
The resistors and capacitors form a low pass filter to attenuate differential-mode and common-mode noise. The filter cutoff frequencies are
\begin{equation}
f_{C_D} = \frac{1}{2 \pi \left( 2(10 k \...
- 466
4
votes
INA128: EMG signal output voltage shift when leg touch the ground
Short story: keep the gain low on the INA128.
Longer story: -
The INA128 Instrumentation amplifier should not have a gain that is higher than about ten (as per your diagram). The reason is that the ...
- 473k
3
votes
Does anyone have advice on homemade EKG/ECG leads?
The most advisable to obtain an ECG signal is to use conventional electrodes. The alternative to the conventions is to use a textile ECG electrode, but this is experimental. You can put "ecg textile ...
- 62
3
votes
why is a GROUND electrode needed with a referential amplifier?
Touch the tip of a 10MOhm scope probe, and you'll likely see 100 or 200 volts at 50 or 60Hz; you are the antenna, the 2nd plate of the capacitor gathering charge from all the power line wiring around ...
- 35k
3
votes
EMG, Muscle Sensor Arduino - Troubleshooting
unfortunately, you've purchased a counterfeit version of our Muscle Sensor v3 which we stopped manufacturing over two years ago when we released our new and improved MyoWare Muscle Sensor. http://www....
3
votes
why is a GROUND electrode needed with a referential amplifier?
The reason is actually because of the buffers.
A simple differential amplifier does not care about the reference point of the input. Without any other common reference, all it cares about is the ...
- 47k
3
votes
Accepted
How to test an EEG?
Aside from generating a signal of a few 10's of microvolts to run through your amps to make sure they're working and verify your frequency cutoffs, you should be able to see clear differences between ...
- 30.6k
3
votes
Accepted
Low-power Li-Ion Battery Charging
There are many charger ICs out there. MCP73831 is one of the cheapest ones.
I have learned a lot from the site below over the years (and I'm involved in making charging, discharging, emulation ...
- 3,626
3
votes
Accepted
How many / which electrodes should I use as input for an RLD (right leg drive)?
Good questions! In addition to the common-mode noise reduction, the amplitude of the common mode voltage must remain small in order for the programmable gain amplifiers to operate at high gains ...
- 11.8k
3
votes
Accepted
How does carbon paste (graphite) interact with other conductors?
Any metal connected to your biological system can create a "battery" - assuming your system includes an electrolyte solution that dissolves some small amount of the metals in your setup. ...
- 4,116
3
votes
Accepted
How does a driven right leg work?
The classic instrumentation amplifier circuit consisting of opamps 1 and 2 in your diagram have a common mode rejection ratio of 0db, otherwise called "no rejection at all". In other words, ...
- 47.3k
3
votes
How does a driven right leg work?
The case for the driven leg can be seen in Winter, Bruce B., and John G. Webster. "Driven-right-leg circuit design." IEEE Transactions on Biomedical Engineering 1 (1983): 62-66..
It becomes ...
- 30.6k
2
votes
Accepted
Building an instrumentation amplifier
The "vref" input of a instrumentation amplifier is just a DC offset on the output. Its use here doesn't convert AC (oscillating) to DC (steady) voltage, but just adds a DC offset to the waveform so ...
- 2,609
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