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  1. eboaylag

    EEG circuit - need help please!

    Alright, so I think the low voltage signal is causing issues. When I try upping the voltage generated, I get a nice sine wave output with values closer to what's expected with the gain of 89. For this, I changed the voltage to 50mV but kept the frequency the same at 20Hz, and I'm getting...
  2. eboaylag

    EEG circuit - need help please!

    I am testing with a Picoscope. I have a frequency generator signal attached to one of the inputs of the AD260, and Channel A is attached to the output of the AD. Grounding causes the scope to flash a red exclamation point, which is bad for the scope. Also, the input is coming out much higher...
  3. eboaylag

    EEG circuit - need help please!

    I don't think the inst. amp. is even working. I've tried switching the AD chip out with the other two I have, but it doesn't make a difference. I've tried changing the resistor to alter the gain, but the oscilloscope shows no change. Is there another way I should be testing this?
  4. eboaylag

    EEG circuit - need help please!

    I've gotten hold of a frequency generator and an oscilloscope to test my circuit. What should I be looking for as I test each stage? I've never used an oscilloscope before.
  5. eboaylag

    EEG circuit - need help please!

    I don't have an oscilloscope, so I was testing with a multimeter, but I don't think it was really an effective way to test. I now have a downloaded oscilloscope https://www.zeitnitz.eu/scope_en, but I still am not getting signals coming through (this oscilloscope is not as good as a physical one...
  6. eboaylag

    EEG circuit - need help please!

    Someone, please help. I'm so behind on this project. It's due in a few weeks. I'm at a loss for what to do. Please help. I have no idea why things aren't working and I don't know how to fix it. Any help is greatly appreciated.
  7. eboaylag

    EEG circuit - need help please!

    I built the circuit, but it's not working. Does anyone have suggestions about what to do ? Could someone check over my layout and make sure everything's alright? Especially the potentiometers. Since they're functioning as variable resistors/rheostats, I've only connect the wiper terminal and...
  8. eboaylag

    EEG circuit - need help please!

    The fake brain is giving me some difficulty. The mp3 player I'm using (iPhone 5c) is said to have a voltage output from 0.8 to 1.2V. My voltage divider consists of a 100k and a 2.2 ohm resistor to bring the voltage between 17-26uV. Plugging the fake brain setup (which has separate mp3s for...
  9. eboaylag

    EEG circuit - need help please!

    Alright, I'll use that to test. I'm in the process of building the circuit now. I built the inst amp and the final amp gain stage together to see if they work, and they do. Going to go stage by stage now for the rest of the circuit! I'll let you know if I run into any problems.
  10. eboaylag

    EEG circuit - need help please!

    Thanks! I never mentioned the time crunch because I didn't want you to feel rushed or obligated. You're doing this as a favor and to help and you've already helped so much, and I feel like I've been asking so many questions. Just know that I really appreciate how much you've helped me!! So, for...
  11. eboaylag

    EEG circuit - need help please!

    Alright, so let's say I choose to do the voltage divider at the end of my circuit. Can I use the 5V output from the Arduino as my offset? In other words, taking the 5V and using two resistors to bring it down to 2.5V, with a cap at the beginning to decouple. If I use values of 22k for both...
  12. eboaylag

    EEG circuit - need help please!

    Also, what film caps are best to use? I bought these: http://www.digikey.com/product-search/en?keywords=399-5443-nd and http://www.digikey.com/product-detail/en/kemet/MMK5225K63J06L4BULK/399-5881-ND/2571316, but the leads turned out to be much shorter than specified so I'm considering buying new...
  13. eboaylag

    EEG circuit - need help please!

    If I did the op amp circuit, would it be like this: http://masteringelectronicsdesign.com/summing-amplifier-calculator-java/ . Where V2 would be created through a voltage divider to bring 9V down to 2.5V, V1 would be my circuit output ranging from ~ -2V to 2V, and Vout1 and Vout2 in the picture...
  14. eboaylag

    EEG circuit - need help please!

    Alright, so with the op-amp would it be like this? Where before R2 could be a simple voltage divider to bring 9V down to 2.5V, and the op-amp would be flipped so it's non-inverting? As for keeping with the voltage divider with cap, when I input capacitance on this calculator at 10uF (which I...
  15. eboaylag

    EEG circuit - need help please!

    @Gryd3 , would this be the way to calculate this? (page 2) I'm finding it pretty difficult to find information about finding this value. Also, would higher values for the voltage divider resistors be better? I already have 270kOhm and 100kOhm resistors to give an offset of around 2.4. I also...
  16. eboaylag

    EEG circuit - need help please!

    As per the ATmega328P datasheet (page 310) the analog input/ADC resistance is 100MOhms. Someone from this site says that it's recommended that whatever's connected to the analog pins has an output impedance of 10k or less. I'm not sure if that helps, but it's what I've found after searching so far.
  17. eboaylag

    EEG circuit - need help please!

    I calculated expected signal ranges (based on alpha and beta waves ranging from 10-60uV): The values are workable, as long as I keep the potentiometer on the final amplifier turned low (towards the gain of 83). I'm looking into buying a higher value resistor to put in the beginning to make the...
  18. eboaylag

    EEG circuit - need help please!

    Haha yeah, it's best that I do research! It helps me understand and makes it easier to communicate with everyone else on here when I have base knowledge of how things are working. Alright, so I'd prefer to go the offset route to keep as much data coming in as possible. Would this offset be...
  19. eboaylag

    EEG circuit - need help please!

    Thanks for bringing this up. This is pretty important to know. Could you explain a bit further what you mean by the options of either cutting the wave in half, or using a decoupling cap and DC offset? These are new terms to me. As far as I can tell (doing quick research), you mean to read in...
  20. eboaylag

    EEG circuit - need help please!

    Alright, so I'm waiting on parts to arrive. I played around in Fritzing to make a layout for the circuit. If someone's willing to check it over and see if there are any issues, I'd really appreciate it. Fresh eyes would probably be the best, especially for the notch filter, which I had a little...
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