Maker Pro
Maker Pro

EEG circuit - need help please!

eboaylag

Jan 7, 2016
46
Joined
Jan 7, 2016
Messages
46
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 another terminal. However, some of the pots have to be grounded. Any advice would be helpful.
EEGNew_Notch_Pot_UPDATED_bb2.png
New_New_Circuit.png
 

eboaylag

Jan 7, 2016
46
Joined
Jan 7, 2016
Messages
46
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.
 

Gryd3

Jun 25, 2014
4,098
Joined
Jun 25, 2014
Messages
4,098
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.
Sorry, missed your other post.
You were building it in stages, testing it as you were going. It sounded like you were making good progress.
What stage has you stumped?
 

Alec_t

Jul 7, 2015
3,587
Joined
Jul 7, 2015
Messages
3,587
The battery wiring doesn't look right in your post 81 Fritzing pic?
Which parts "aren't working", and in what way?
 

eboaylag

Jan 7, 2016
46
Joined
Jan 7, 2016
Messages
46
You were building it in stages, testing it as you were going. It sounded like you were making good progress.
What stage has you stumped?

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 because signals below 20Hz are probably being disregarded by the audio input, but it's better than nothing, I think). I don't have the fake brain to use because the signals were fluctating heavily and the voltage divider to bring the fake brain down to "brain wave level" was not working. I have tried using my pulse as an easy input by attaching electrodes to my wrists, but I still do not see any signal in any part of the oscilloscope.

The battery wiring doesn't look right in your post 81 Fritzing pic?
Which parts "aren't working", and in what way?

The top-most power strip is "ground", created through the negative terminal of one battery and the positive terminal of another. Below that is negative power, below that is positive power, and below that is ground again.
741-9v.gif
If this is incorrect, please let me know how you believe I should fix it!
 

eboaylag

Jan 7, 2016
46
Joined
Jan 7, 2016
Messages
46
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.
 

Gryd3

Jun 25, 2014
4,098
Joined
Jun 25, 2014
Messages
4,098
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.
You built it, you remember what the stages do.
Connect your signal generator to the input of any of the stages, and check the output of the same stage.
As you adjust the frequency of the signal generator , you should witness the amplitude of the output decrease when you reach and exceed the cutoff frequency for the bandpass filter you designed.
If the output does not behave as expected, then you need to revisit that stage and make sure it's built properly.
 

eboaylag

Jan 7, 2016
46
Joined
Jan 7, 2016
Messages
46
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?
 

Gryd3

Jun 25, 2014
4,098
Joined
Jun 25, 2014
Messages
4,098
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?
Please share how you are testing it.
There are two inputs. The inst. amp. will show the 'difference' between the inputs.
If you see no output, use the scope to confirm the signal on both inputs. Put Channel A on input +, and Channel B on input - . If the scope has the option you can add or subtract the channels from each other. The Inst. Amp does this, but also amplifies the output... so doing this on the scope first should give you an idea what what will appear on the other side.
Additionally, you can put Channel A on one of the inputs. Ground the other input, and put Channel B on the output. This will let you see instantly what goes in and comes out. Because one of the inputs is grounded, what goes in should be what comes out. (Although at a higher level)
 

eboaylag

Jan 7, 2016
46
Joined
Jan 7, 2016
Messages
46
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 than expected. The signal I have going in is a 20Hz sine wave at 20uV. My expected output wave would be 89*0.00002V, which is 0.00178V. Attached is a photo with measurements, with the trigger set to where it made the wave stable. I attributed the excess voltage coming out to noise, but I'm not sure if it really is all noise or just a non-working part.
PIco_Scope_ADOutput.png
 

eboaylag

Jan 7, 2016
46
Joined
Jan 7, 2016
Messages
46
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 voltages of around 4.5V max and -4.22V min, which is close to the expected 89*0.05V = 4.45V. This is with one input grounded and the other receiving signal from the signal generator. I think I'll try testing the rest of the circuit with these higher millivolt voltages just to be sure things are working.
This does concern me, though, since the actual inputs of brainwaves are going to be in the microvolt range.
50m_VPico.png
 

Gryd3

Jun 25, 2014
4,098
Joined
Jun 25, 2014
Messages
4,098
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 than expected. The signal I have going in is a 20Hz sine wave at 20uV. My expected output wave would be 89*0.00002V, which is 0.00178V. Attached is a photo with measurements, with the trigger set to where it made the wave stable. I attributed the excess voltage coming out to noise, but I'm not sure if it really is all noise or just a non-working part.
PIco_Scope_ADOutput.png
Approx 13MHz != 20Hz . This is not the signal you put in.

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 voltages of around 4.5V max and -4.22V min, which is close to the expected 89*0.05V = 4.45V. This is with one input grounded and the other receiving signal from the signal generator. I think I'll try testing the rest of the circuit with these higher millivolt voltages just to be sure things are working.
This does concern me, though, since the actual inputs of brainwaves are going to be in the microvolt range.
50m_VPico.png
Glad you got that part ironed out, please keep us posted. I'm unsure at the moment why it would not work with the lower voltage. I will need to dig into the datasheet to see what I can find.
 
Top