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  • AlanA47 followed Electronics, Audio, LEDs, Props & Accessories and 2 others channel 1 month ago
  • AlanA47 commented on cah6's instructable DIY EEG (and ECG) Circuit1 month ago
    DIY EEG (and ECG) Circuit

    Hi,So, I actually ran into the same issue building the circuit. Rather than deal with the uni-directional capacitors and track down the current to make sure everything was hooked up properly, I just got some ceramic caps for those instead of tantalum. The diagram called for bi-directional caps, so I decided to trust that instead of the material that was called for in write-up (which never references the fact that the tantalum caps have a direction anyway).

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  • AlanA47 commented on cah6's instructable DIY EEG (and ECG) Circuit9 months ago
    DIY EEG (and ECG) Circuit

    It depends on several factors, but, in short, not really. Of course it is entirely feasible for you to switch out that 560 ohm resistor for another to increase the gain (all the way up to 10,000 if you felt like it, following the specifications of the instrumentation amplifier and the formula provided to determine the gain) and it would be then entirely possible to read it on an oscilloscope, provided your scope had the proper specifications (bandwith, min/max input voltage, etc.). The problem I foresee here though is that these filters that are included are entirely necessary for a few reasons. Even if you have built-in low and high pass filters on you oscilloscope to satisfy the Nyquist Criterion in order to even read the frequency spectrum, you still willl invariably need that 60 Hz ...see more »It depends on several factors, but, in short, not really. Of course it is entirely feasible for you to switch out that 560 ohm resistor for another to increase the gain (all the way up to 10,000 if you felt like it, following the specifications of the instrumentation amplifier and the formula provided to determine the gain) and it would be then entirely possible to read it on an oscilloscope, provided your scope had the proper specifications (bandwith, min/max input voltage, etc.). The problem I foresee here though is that these filters that are included are entirely necessary for a few reasons. Even if you have built-in low and high pass filters on you oscilloscope to satisfy the Nyquist Criterion in order to even read the frequency spectrum, you still willl invariably need that 60 Hz noise filter. Let me provide an example to show you what I mean. If you read a signal of say, 12 microvolts, then amplify it 10,000 times, but you don't remove any of the noise, you've amplified the ambient voltage from your lights and your computer, and whatever nearby electronics there are, also by 10,000 times. So, if you went to read the signal then, you would only see random fluctuations of ambient noise and you would have much less signal than you do noise, so chances are you wouldn't see any noticeable movement based on what you were thinking or doing with your body from the eeg signal, because your noise was amplified so much it was covering up any signal you may be trying to measure. But, if we do it as above, providing a small pre-amplification, then filtering out noise (like 60Hz electrical hum), then amplified the signal the rest of the way to whatever your desired amplification is, you will only have amplied your signal (at least in an ideal circuit) and you could easily measure that on your scope.

    It depends on several factors, but, in short, not really. Of course it is entirely feasible for you to switch out that 560 ohm resistor for another to increase the gain (all the way up to 10,000 if you felt like it, following the specifications of the instrumentation amplifier and the formula provided to determine the gain) and it would be then entirely possible to read it on an oscilloscope, provided your scope had the proper specifications (bandwith, min/max input voltage, etc.). The problem I foresee here though is that these filters that are included are entirely necessary for a few reasons. Even if you have built-in low and high pass filters on you oscilloscope to satisfy the Nyquist Criterion in order to even read the frequency spectrum, you still willl invariably need that 60 Hz ...see more »It depends on several factors, but, in short, not really. Of course it is entirely feasible for you to switch out that 560 ohm resistor for another to increase the gain (all the way up to 10,000 if you felt like it, following the specifications of the instrumentation amplifier and the formula provided to determine the gain) and it would be then entirely possible to read it on an oscilloscope, provided your scope had the proper specifications (bandwith, min/max input voltage, etc.). The problem I foresee here though is that these filters that are included are entirely necessary for a few reasons. Even if you have built-in low and high pass filters on you oscilloscope to satisfy the Nyquist Criterion in order to even read the frequency spectrum, you still willl invariably need that 60 Hz noise filter. Let me provide an example to show you what I mean. If you read a signal of say, 12 microvolts, then amplify it 10,000 times, but you don't remove any of the noise, you've amplified the ambient voltage from your lights and your computer, and whatever nearby electronics there are, also by 10,000 times. So, if you went to read the signal then, you would only see random fluctuations of ambient noise and you would have much less signal than you do noise, so chances are you wouldn't see any noticeable movement based on what you were thinking or doing with your body from the eeg signal, because your noise was amplified so much it was covering up any signal you may be trying to measure. But, if we do it as above, providing a small pre-amplification, then filtering out noise (like 60Hz electrical hum), then amplified the signal the rest of the way to whatever your desired amplification is, you will only have amplied your signal (at least in an ideal circuit) and you could easily measure that on your scope.

    It depends on several factors, but, in short, not really. Of course it is entirely feasible for you to switch out that 560 ohm resistor for another to increase the gain (all the way up to 10,000 if you felt like it, following the specifications of the instrumentation amplifier and the formula provided to determine the gain) and it would be then entirely possible to read it on an oscilloscope, provided your scope had the proper specifications (bandwith, min/max input voltage, etc.). The problem I foresee here though is that these filters that are included are entirely necessary for a few reasons. Even if you have built-in low and high pass filters on you oscilloscope to satisfy the Nyquist Criterion in order to even read the frequency spectrum, you still willl invariably need that 60 Hz ...see more »It depends on several factors, but, in short, not really. Of course it is entirely feasible for you to switch out that 560 ohm resistor for another to increase the gain (all the way up to 10,000 if you felt like it, following the specifications of the instrumentation amplifier and the formula provided to determine the gain) and it would be then entirely possible to read it on an oscilloscope, provided your scope had the proper specifications (bandwith, min/max input voltage, etc.). The problem I foresee here though is that these filters that are included are entirely necessary for a few reasons. Even if you have built-in low and high pass filters on you oscilloscope to satisfy the Nyquist Criterion in order to even read the frequency spectrum, you still willl invariably need that 60 Hz noise filter. Let me provide an example to show you what I mean. If you read a signal of say, 12 microvolts, then amplify it 10,000 times, but you don't remove any of the noise, you've amplified the ambient voltage from your lights and your computer, and whatever nearby electronics there are, also by 10,000 times. So, if you went to read the signal then, you would only see random fluctuations of ambient noise and you would have much less signal than you do noise, so chances are you wouldn't see any noticeable movement based on what you were thinking or doing with your body from the eeg signal, because your noise was amplified so much it was covering up any signal you may be trying to measure. But, if we do it as above, providing a small pre-amplification, then filtering out noise (like 60Hz electrical hum), then amplified the signal the rest of the way to whatever your desired amplification is, you will only have amplied your signal (at least in an ideal circuit) and you could easily measure that on your scope.

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  • AlanA47 commented on cah6's instructable DIY EEG (and ECG) Circuit9 months ago
    DIY EEG (and ECG) Circuit

    Hopefully, I'm understanding your question correctly. As far as why many of these types of circuits use an ADC, the reasoning behind this has to do with optimization for more complex circuits. While, in a simple EEG setup like this one, an analog cable such as the 3.5mm one used here is fine for relaying the data to the computer, but in larger systems it's not as efficient. In systems with, say, 16 channels, you would use an analog multiplexer to to read and pass all of these various signals to your high-speed ADC which would then allow you to pass it all at once through a bus (like a USB) to your computer which can then read it all without the need for the added complexity of keeping your analog signals isolated. Though there's not much reason to build this section yourself, both for t...see more »Hopefully, I'm understanding your question correctly. As far as why many of these types of circuits use an ADC, the reasoning behind this has to do with optimization for more complex circuits. While, in a simple EEG setup like this one, an analog cable such as the 3.5mm one used here is fine for relaying the data to the computer, but in larger systems it's not as efficient. In systems with, say, 16 channels, you would use an analog multiplexer to to read and pass all of these various signals to your high-speed ADC which would then allow you to pass it all at once through a bus (like a USB) to your computer which can then read it all without the need for the added complexity of keeping your analog signals isolated. Though there's not much reason to build this section yourself, both for the added complexity and cost as well as decreased reliability, and you could easily accomplish this by passing your signal into a pre-built micro-controller like an Arduino or something and hooking that straight up with a USB to your computer. I hope that answers your question.

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  • AlanA47 commented on cah6's instructable DIY EEG (and ECG) Circuit10 months ago
    DIY EEG (and ECG) Circuit

    no you don't need the gel anymore if you go the helmet route, the electrodes are dry electrodes. They run slightly more expensive, but are definitely worth it.

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