I then soldered everything together and the board was ready for chapter two.
The next big challenge was to flash the firmwares, but with a lot of research in the forum and on google plus a lot of patience it was finally possible. Here the final result!

I have a bit of packet loss (2-4%) I think due to the thickness of the board and the length of the copper-wire-vias but it works super fine for me…
I also built some active electrodes but I’ll probably make another post dedicated to that.
The next journey will be to build an uploaded/modern version of the Cyton (plus integrated daisy) since the technology used by OpenBCI was good 10-15 years ago but it’s now pretty obsolete and one of the most important component (the RFD22301) is not in production anymore and a pretty old technology. So I hope that I can give you some news soon.
Thanks for reading

I'm Mariana, a Information System undergrad from Brazil, and I'm building a DIY EEG headset from scratch for my thesis. I'm a complete beginner in hardware, but I've been studying every component carefully before purchasing anything.

Here's the architecture I'm planning:

• Ag/AgCl electrodes at Fp1, Fp2, F3, F4 (10-20 system)
• Passive RC filters at the input — anti-aliasing and RF protection
• ADS1299 as the analog front-end — internal PGA, 24-bit, 8 channels
• LiPo battery for isolated power supply (no wall power on the headset side)
• Optical isolator on the SPI data channel — to physically separate the headset from the ESP32
• ESP32 for Bluetooth transmission to PC
• BrainFlow for data streaming

Before I buy anything, I have a few questions:

1. Does this architecture make sense for a functional EEG headset?
2. Is the optical isolator on the SPI channel the right approach, or is there a better way to handle isolation?
3. Any components I should swap or add?
4. What are the most common mistakes beginners make at this stage?

Any feedback is hugely appreciated. Thank you!

I have tried my best to search for relevant posts on the forum. Although some people mentioned similar issues, I have not found an accurate solution or explanation.

Many Thanks！！

Images:
DesignSpark

BOM:

Schematics:

I’m currently working on building my own Cyton board. I could manage to flash my PIC32 successfully but I’m struggling to flash the radio codes for HOST and DEVICE (newest version on GitHub) I’m using arduino IDE v1.6.6 and the Rfduino version 2.3.3 package. When I try to compile the codes I always get: “ exit status 1 class RFduinoGZLLClass' has no member named 'channel'”. Is there a way to compile the codes on this IDE (because the version 1.5.8 is not to find anymore). Or am I missing something?
Could someone please help me with this issue?
Thanks in advance!

I've been working on a custom EEG device using the ADS1299 AFE, loosely based on the OpenBCI Cyton design. I implemented the Cyton bias network 1-to-1, with similar components (as can be seen in Fig. 1). Additionally, I must note that I have been using a bipolar power supply with the ADS in single-ended mode. The N side of the PGAs is used as the analog input, and SRB2 is active as the reference electrode.

Some of my register settings:
CONFIG2: 11000000
CONFIG3: 11101100
CHset (all channels): 01101000
BIAS_SENSN: 00100001
BIAS_SENSP: 00000000

Fig. 1: Simplified custom schematic on my board

This design has worked, just unreliably. The bias drive has an unstable behavior where it will sometimes lock in and produce a stable inverted voltage to keep all of the electrodes relatively centered on the ADS's range. See Fig. 2 for some good EEG data readout.

However, if any of the electrodes that add to the bias generation (specified with the BIAS_SENSN register) lose contact with the patient, wild oscillations start up in the bias electrode and all other electrodes subsequently. If the electrode is reattached, the oscillations eventually die back down, but not always. These oscillations seem to have a RC-like timing characteristic, since they change frequency depending on what I can assume is the impedance of the electrodes that contribute to them. See Figures 3, 4, 5 for the unstable oscillations.

Fig. 2: Stable EEG data output with bias connected.

Fig. 3: Oscillating, low frequency behavior.

Fig. 4: Higher frequency oscillating behavior.

Fig. 5: Oscillating behavior when trying to adjust electrodes, showing variable frequency oscillations.

This behavior only occurs when the bias is connected. If I turn the bias amp off or just leave it disconnected, then there's no instability with the EEG readings: the only issue is that without the bias, the system cannot cancel out 60Hz line noise as effectively, and the system becomes much more sensitive to common mode noise.

My guess is that this behavior is a result of the bias drive network not being tuned properly. I know another post was made recently talking about BIASINV and how leaving it floating may contribute to the instability -- especially if there are no channels contributing to the bias. However, I'm posting here to see if any of you have seen this behavior before with the OpenBCI Cyton, and if so, what solutions worked to fix it.

I would really like to use this bias amplifier in my design as it greatly improves the data readout when it works. But I need to find a solution to keep it stable -- without that, the readings are useless.

TL;DR: The ADS1299 bias amplifier appears to have some unstable behavior that causes oscillations in the electrode readings. What can be done to remove these and make the bias amp stable again?

Thank you,
Reagan

Thanks!

I am a robotics engineer based in London and I have interest in sensing and electronics. As a part of a personal project, I want to design my own EEG setup (potentially to control a robot). I stumbled open work done by other people/companies, and the ADC of choice seems to be the ADS1299 from Texas Instrument.

I have a lot of experience with analog PCBs (I design PCBs for guitar amps), however I never had the chance to do SMD boards for sensing: I figured this would be a great learning experience

I have created my schematics and layouts in Eagle and the board is basically completed. I would love to have some expert opinion o the results, and any suggestions you might have that might increase the chances of success

A couple of things to note/doubts:

• I'm using a 2 layers PCB

• ground planes and fence vias on both sides

• I'm using an external oscillator for the clock: not sure the location of it on the board is best to avoid noise/interference

• I tried to separate the analog and digital signals, not sure if this is the best practice

• I'll be using SPI communication with a Raspberry PI (never used SPI before, so I hope the wiring is correct)

• I kept the supply and filtering components quite far from the chip and the digital signals as much as possible

Please let me know your thoughts, hope to learn more about circuit design and add some knowledge to my toolbox

Andrea

Now, can you tell me what might be wrong and what should I do next? gratitude!

I am working on a custom board based on Cyton board. I need to change a few things on the bootloader for my board.

Is it possible to get the source code for UDB32-MX2-DIP bootloader? I need to swap RX and TX pins for the bootloader, I realized that they are connected to remappable pins on the PIC as many pins are remappable.

Thanks!

Github link to the bootloader: https://github.com/openbci-archive/UDB32-MX2-DIP

DC offset.
One of the reasons that can cause these noises can be a large displacement between the reference electrode and the rest of the electrodes. The problem is not even the magnitude of this offset, but its change over time. The rate of this change can be fast enough to generate noise in the Delta range.
See Figure 7 for real EEG DC offset and Figure 8 for emulator DC offset.

Analysis using fragmentation.
The idea is that the entire data array is divided into small fragments.
Then, for each fragment, the FFT is performed and the TBR is calculated.
Then all fragments are sorted in ascending order of TBR and presented in graphical form.
In the figures below, you can see that for "good" records, only a small number of fragments have an abnormally high TBR and a clear boundary is visible between them and normal fragments. For "bad" records, such a boundary does not exist.

I really appreciate your help!
kidoom4@gmail.com

NOTE: The chipKIT github hosts a relatively newer version of UDB32_MX2_DIP.hex (~189 kB) which has been compiled by a newer version of MPLAB, but for some reason, the new one is NOT recognized as a valid firmware by their own IDE or IPE when you attempt to import or load the hex for flashing. Strange, I know.. but just thought I should mention this, incase someone experiences the same issue. Anyway, I stuck with the older version of the bootloader provided here on OBCI's Github archive (which is only ~8kb)
.
Next: Opened MPLAB IPE v4.15 (I havent installed their more recent v5+/v6+ versions, in the interest of saving space on my drive). Set the ICSP option to "Power Target Circuit from Tool" and then clicked Connect. PICKit3 detected the PIC32 chip successfully and this was the initial log output:

    Connecting to MPLAB PICkit 3...

    Currently loaded firmware on PICkit 3
    Firmware Suite Version.....01.51.08
    Firmware type..............PIC32MX

    Programmer to target power is enabled - VDD = 3.300000 volts.
    Target device PIC32MX250F128B found.
    Device ID Revision = A1

I loaded the working version of the UDB32_MX2_DIP.hex bootloader and was able to burn it successfully to the chip using PICKit3, that went well. The blue LED started blinking gleefully, so I knew it was ready to accept new code. So far, so good!
.
Next, I attempted to upload the DefaultBoard sketch to the PIC from within Arduino. I figured that since the bootloader was already flashed, it should be able to accept the firmware OTA, so I switched the Port# to that of the Dongle (which had already been flashed with RadioHost32.hex by now). The compilation was successful, however the upload failed. Please see the error as displayed below:

.
Out of curiosity, I decided to see what would happen if I flashed the PIC with a blank sketch instead, and lo & behold, that was flashed successfully to the PIC! (see below):

Coming back to the Cyton firmware: I tried uploading DefaultBoard several times, checked all the wiring, brought the RFDuinos closer to each other, etc.. but nothing helps. Btw, I've already read through this entire detailed thread for clues but none of the tips have worked for me at all: chipKIT uploading tips & restarting bootloader

.
Finally, I abandoned the Arduino-RFDuino-PIC route and decided to flash the firmware directly using PICkit itself. Copied the compiled DefaultBoard.ino.hex file from the Temp folder and placed it in a more convenient location. Loaded the DefaultBoard firmware hex into IPE, clicked Program and this is the error that results:

.
When I try to Erase the chip and do a Blank Check immediately after, the blank check fails with a similar error:

Blank Checking...
Program memory is not blank.
Blank check complete, device is not blank.

Seems to be an issue with writing to the chip's Flash starting from memory address 0x1d010000 onwards, I deduced this after running Verify.. this was the result:

Verifying...

The following memory areas(s) will be verified:
program memory: start address = 0x1d000000, end address = 0x1d01ffff
boot config memory
configuration memory

program memory
Address: 1d010000 Expected Value: 10600028 Received Value: 0
Verify failed

I do suspect that this Program Flash region is being write-protected, so is there a specific #pragma or predirective that needs to be specified in the code in order to disable the chip's protection scheme?

I also read on another forum that one person was able to get past this error by programming the PIC in Low-Voltage mode, while they weren't able to do so in regular mode. But I dont see anything specific about LVP mentioned in this PIC32's datasheet, does anyone have any information or clues to this??

.
Tagging @wjcroft , @Shirley , @retiutut for any help & guidance in this matter

I'm part of a senior design undergraduate engineering team attempting to use the Cyton board in an EEG project. We've built the board ourselves following a method similar to @alwayswearshats' procedure described here, albeit using a wired USB connection instead of the WiFi Shield. We're able to detect the Cyton board in the GUI and start a session, but receive a data streaming error after clicking the "Start Data Stream" button. We were able to successfully install firmware to the board from Arduino IDE and verified sending and consuming I/O between the board and computer. In rudimentary testing we know board.streaming is always false and so is board.channelDataAvailable. I have two main questions:

1. How might we root cause the problem?
2. Can any methods in the library be used to test if our sampling chip is dead?

I've included screenshots from the OpenBCI GUI below and attached the output from the console.

Thanks!

The first problem is, although the board can start session with GUI, it can't start streaming with version 5.0.4 and further version, I'm guessing if there is any change in the protocol that I don't know. It can open an access point with WiFi.softAP(ssid, password) this sentence, and my PC can connect this AP, but the streaming can't start. The log shows that Exception when starting stream, Errror in start_stream:BOARD_WRITE_ERROR. I have looked the source code of the GUI, but the code is way too complex, I can't locate what cause this problem.

The second problem is, I have set the default state of the ADS1299, my tutor's document said it should be BIAS DON'T INCLUDE & SRB1 OFF & SRB2 OFF, and that's what I write into the register CHnSET, I found that every channel is actually in the state I had set. But the GUI can't read my settings for every channel, it shows BIAS INCLUDE & SRB2 ON & SRB1 OFF in the Hardware Settings. But the other code project of my board, which is based on serial transfer, the hardware settings will be read actually by the GUI. Why the GUI can't read my settings for ADS1299 in CHnSET register?

And the third problem is the new one, when my PC get connect to my board's AP , what I supposed to do is start up the GUI right? But when I finished the Cyton settings and clicked the start system button, the GUI did not change into the analysis window that contains FFT diagram and wave and etc but showed what it was before I clicked the button which was empty. And I clicked the button again, the GUI finally showed the full diagram and can start the data stream.

Can you point me to the part in the code of OpenBCI_GUI where this is done? I have seen the scan_channels function in here, but that does not seem to answer my question.
My problem is that I have made my own cyton board and the serial channel does not show up in the GUI, while it shows up in custom software I'm currently developing. So the hardware connection is working. I 'think' the messages my board sends are identical to your reference, though.

Do you have ported the design files to any open source PCB design program, or at least to something that does not require a windows machine ?

I'm trying to build the futon board for my project - can I use ADS1298 instead ADS1299 - Is there any specific advantage to using 1299? If so please let me know.

We recently got OpenBCI Cyton and Dongle printed and assembled.

I would like to know what is the correct procedure to follow to program freshly printed cyton and dongle.

@wjcroft @retiutut Appreciate your help on this.

Regards,
Pluto

I have a few queries on the ADS1299 connection to PIC32. There are 2 ADS1299 - the cyton is master and daisy is a slave. With PIC32 acting as Master - Cyton ADS1299 will be Slave1 and Daisy ADS1299 as Slave 2.

In this case, if both the ADS had to function simultaneously (where Daisy CLK will be grounded, therefore both ADS runs on the CYTON ADS CLK (as suggested in your docs)). Now I would like to know how both ADS (MOSI (PIN34) and MISO (PIN43) are connected to PIC32 (MOSI (PIN3) and MISO(PIN22).

ADS_CYTON - MOSI to PIC32 MOSI
ADS_DAISY - MOSI to PIC32 MOSI
ADS_CYTON - MISO to PIC MISO
ADS_DIAYS - MISO to PIC MISO

Meaning both ADS get directly connected to the PIC for simultaneous processing.
or
ADS_CYTON - MOSI to PIC32 MOSI
ADS_CYTON - MISO to ADS_DAISY MOSI
ADS_DAISY - MISO to PIC MISO

Please suggest the best connection for both ADS to work simultaneously with microcontroller.

Looking forward to a suggestion.

regards
Ankit

I know this sounds like such a noob question but is there any other way I can determine the polarity of the TVS diode?? I dont want to solder it incorrectly and then fry something on the board in the process, lol
I will have further questions down the line, but I need to get this sorted out first.

The device (circa 2000) is a through-brain current modulated with a randomized mix of frequencies centering near natural brainwave frequencies.

Below is TeslaTech's video demonstrating and discussing the theory of Gerlator's TES device that can be seen by paid membership only, shucky darn.

Any information is helpful!