applying signal generator to Cyton, ramp wave form
I tried connecting the cyton to a function generator which had a ramp wave at 100 Hz and amplitude of 20 mV. The function generator output was connected to channel 2P (top pin) and the function generator ground was connected to SRBN (bottom pin). I also tried connecting the ground to AGND N (bottom) but it didn't improve results.
The GUI time series plot looked nothing like the input ramp signal. Is my cyton broken? What should I do?
(I connected the function generator to the osciloscope and the waveform looked fine, so it's not a problem with the function generator)
Comments
Use the same pins for your test as you use for EEG: the pins closest to the board, the 'bottom' pins. Both channel pin and SRB2. Be careful in applying equipment voltages to the input pins. If signal level is beyond a few volts it may damage the ADS1299 chip.
The recommended way to confirm your Cyton, is to just use the eyes-closed Alpha generation test:
https://docs.openbci.com/GettingStarted/Biosensing-Setups/EEGSetup/#4-alpha-brain-waves-eeg
William
Hi,
I tried using the new configuration (channel 4 bottom pin, SRB2 bottom pin), but the plots didn't make any sense.
I have attached below, please see, I would really appreciate insight. All waves 610mV and 10Hz.
Sine Wave
ramp wave
square wave
And here are shots of the oscilloscope connected to the function generator. Channel 4 doesn't resemble for any
Hi SigCraft,
Did you see my previous link suggestion for trying an eye-closed alpha test?? That is the BEST test you can try.
Your graphs and FFT show a HUGE amount of mains noise, harmonics and subharmonics. Most likely your signal generator equipment is at fault somehow with it's grounding configuration. You want NO ground connections, just plus and minus signal. Also your channel 4 signal and SRB2, is bleeding into all other channels. Another sign that something is wonky with your SRB2 connection.
Finally the .6V signal you are applying is WAY WAY larger than typical EEG, which is only a few tens of microvolts. You can make a voltage divider to drop your generator to microvolt levels:
https://ohmslawcalculator.com/voltage-divider-calculator
William
Hi, thank you for your response. I need to use the function generator for the research project, alpha test is not an option.
I have attached an image of the wiring here: the jumper from SRB2 is connect the black lead of the function generator, and the jumper from 4CH to the red lead of the function generator, When you say there should be no ground connections, should the black lead not be connected to anything? Are both SRB2 and 4CH supposed to be connected to the red lead?
Additionally this is to test for EMG not EEG, if that matters.
Please check the EEG alpha generation. At least that will verify your Cyton is working. Even if it does not qualify for your research requirement. The FFT showing huge mains noise and channel coupling is conclusive that your signal generator or nearby equipment is somehow doing this. Some generation equipment connects the 'black' or ground lead to the mains ground pin.
How long have you had this Cyton / purchase date? Has it worked in the past? Have you had any problems in the past?
Other things that can cause large mains noise: metallic tables, cabinets, extension cords, power supplies, conduits in walls, floors, ceilings, etc. There are EMF measurement meters available that can alert you to nearby fields. Cyton channels that do not have any connections, can act as antennas picking up nearby EMF noise.
Your connections are also ignoring the Cyton Bias / Ground pin. Which acts to reduce noise interference.
https://docs.openbci.com/GettingStarted/Biosensing-Setups/EEGSetup/#4-alpha-brain-waves-eeg
Now looking at your wiring photo again. You appear to be using a wall power supply / transformer. Is that correct. Please replace this with the AA battery pack or a LiPo cell. Many wall power supplies will have either mains noise (your case) or boost converter (switching power supply) noise. The Cyton uses linear voltage regulators, but this mains noise is probably being coupled in via inductive or capacitive coupling from the AC wall powered supply.
If I may, and I'm probably wrong here,
Looking at @bci_sigcraft 's resulting waves from the time series, it reminded me of the Decimation Filter Frequency Response described in ADS1299 data sheet, passing through the Sinc Filter depicted here:
Your resulting waveforms look a lot like they might have passed through a filter like that.
My guess is, as @wjcroft mentioned, you're feeding it way too high of an amplitude at 600 mV, which I'm guessing is also passing through the default PGA settings at x24 Gain, resulting in the signal overshooting the capacity of the amplifiers and you'll lose linearity of the filter's response and end up with what you shared.
Also from the data sheet:
It'll be cool if that's what's going on here!
The AVDD AVSS values are plus and minus 2.5 volts, see the schematic,
https://docs.openbci.com/assets/images/OBCI_V3_32bit-Schematic-1930fe4303e214795b38b75ba7b35b75.jpg
So the 600mV being applied is not within 200mV of the supply rails.
If @bci_sigcraft can confirm that they have resolved the issue by using batteries, that would be helpful.
William
Hi,
Thank you @wjcroft and @mhrahmani! I will try with a battery and smaller input voltage!