Cyton Dongle
USB wireless receiver (RFD22301/RFDuino) for OpenBCI Cyton 8/16-channel EEG board.
Hardware
- Dongle: FTDI FT231X USB-UART → RFDuino 2.4 GHz radio
- Serial: 115200 baud, 8N1
- Device:
/dev/cu.usbserial-*(macOS) or/dev/ttyUSB*(Linux) - Sample Rate: 250 Hz
- Channels: 8 (Cyton) or 16 (Cyton + Daisy)
- Packet: 33 bytes (0xA0 start, 24 bytes channel data, 6 bytes aux, 1 byte counter, 0xC0 stop)
First-Time Pairing (Critical)
A new dongle and board are typically on different radio channels. The standard 0xF0 0x01 channel-set command requires both sides to handshake — it fails when they're on different channels.
Use 0xF0 0x02 (CHANNEL_SET_OVERRIDE) to force the dongle to each channel without requiring board response, then check system status:
import serial, time
ser = serial.Serial('/dev/cu.usbserial-XXXXX', 115200, timeout=2)
time.sleep(2)
for chan in range(26):
ser.reset_input_buffer()
ser.write(bytes([0xF0, 0x02, chan])) # override dongle (no handshake)
time.sleep(0.5)
ser.read(ser.in_waiting or 512)
ser.reset_input_buffer()
ser.write(bytes([0xF0, 0x07])) # system status query
time.sleep(0.5)
resp = ser.read(ser.in_waiting or 512).decode('utf-8', errors='ignore')
if 'System is Up' in resp:
print(f'FOUND BOARD ON CHANNEL {chan}')
break
else:
print(f'Ch {chan}: Down')
ser.close()
Radio Commands (0xF0 prefix)
| Bytes | Command | Notes |
|---|---|---|
0xF0 0x00 |
CHANNEL_GET | Returns current dongle channel |
0xF0 0x01 <ch> |
CHANNEL_SET | Coordinated change, requires board online |
0xF0 0x02 <ch> |
CHANNEL_OVERRIDE | Dongle-only, no handshake — use for pairing |
0xF0 0x03 |
POLL_TIME_GET | Current poll time |
0xF0 0x04 <t> |
POLL_TIME_SET | Set poll time |
0xF0 0x05 |
BAUD_DEFAULT | 115200 |
0xF0 0x06 |
BAUD_FAST | 230400 |
0xF0 0x07 |
SYS_STATUS | "System is Up" or "System is Down" |
0xF0 0x0A |
BAUD_HYPER | 921600 |
Channels are 0-25. Default for new boards is usually 1.
Serial Commands
| Cmd | Action |
|---|---|
v |
Firmware version + board info |
b |
Start binary streaming |
s |
Stop streaming |
C |
Enable Daisy (16ch mode) |
D |
Query Daisy module |
? |
Print ADS1299 registers |
1-8 |
Default channel settings (ch 1-8) |
!-* |
Default channel settings (ch 9-16, Daisy) |
d |
Reset all channel defaults |
Parsing Binary Packets
SCALE_UV = 4.5 / (24 * (2**23 - 1)) * 1e6 # ~0.02235 uV/count
def parse_24bit(b0, b1, b2):
val = (b0 << 16) | (b1 << 8) | b2
return val - 0x1000000 if val >= 0x800000 else val
33-byte packet: 0xA0 | sample_num | 8×3-byte channels | 6-byte aux | 0xC0
With Daisy: odd sample numbers = channels 1-8, even = channels 9-16.
Streaming and Channel Quality Check
import serial, time, math
ser = serial.Serial('/dev/cu.usbserial-XXXXX', 115200, timeout=5)
time.sleep(2)
ser.reset_input_buffer()
# Override to known channel
ser.write(bytes([0xF0, 0x02, CHANNEL]))
time.sleep(1)
ser.read(ser.in_waiting or 512)
# Reset board
ser.write(b'v')
time.sleep(3)
ser.read(ser.in_waiting or 4096)
ser.reset_input_buffer()
SCALE_UV = 4.5 / (24 * (2**23 - 1)) * 1e6
def p24(b0, b1, b2):
v = (b0 << 16) | (b1 << 8) | b2
return v - 0x1000000 if v >= 0x800000 else v
# Start stream
ser.write(b'b')
time.sleep(1.5)
ser.read(ser.in_waiting or 2048) # drain text
samples = {i: [] for i in range(16)}
t0 = time.time()
while (time.time() - t0) < 4:
avail = ser.in_waiting
if not avail:
time.sleep(0.01)
continue
buf = ser.read(avail)
i = 0
while i < len(buf) - 32:
if buf[i] == 0xA0 and buf[i+32] == 0xC0:
sn = buf[i+1]
is_daisy = (sn % 2 == 0)
for ch in range(8):
off = i + 2 + ch * 3
raw = p24(buf[off], buf[off+1], buf[off+2])
samples[ch + (8 if is_daisy else 0)].append(raw * SCALE_UV)
i += 33
else:
i += 1
ser.write(b's')
ser.close()
# Assess quality
for ch in range(16):
vals = samples[ch]
if len(vals) < 10:
print(f'Ch {ch+1}: NO DATA')
continue
mean = sum(vals) / len(vals)
std = math.sqrt(sum((v - mean)**2 for v in vals) / len(vals))
if abs(mean) > 187000: q = 'RAILED'
elif std < 1: q = 'FLAT'
elif std > 200: q = 'BAD CONTACT'
elif std > 100: q = 'NOISY'
elif std < 50: q = 'CLEAN'
else: q = 'OK'
print(f'Ch {ch+1}: {q} (std={std:.1f} uV)')
Ultracortex Mark IV 16ch Montage (10-20)
| Ch | Position | Ch | Position |
|---|---|---|---|
| 1 | Fp1 | 9 | F7 |
| 2 | Fp2 | 10 | F8 |
| 3 | C3 | 11 | F3 |
| 4 | C4 | 12 | F4 |
| 5 | P7 | 13 | T7 |
| 6 | P8 | 14 | T8 |
| 7 | O1 | 15 | P3 |
| 8 | O2 | 16 | P4 |
Daisy Module (16ch)
The Daisy stacks on top of the Cyton, adding a second ADS1299 for channels 9-16.
Verifying Daisy:
vshould report:On Daisy ADS1299 Device ID: 0x3EDreturns Daisy firmware version (e.g.,060110)Cenables 16ch mode, returns16c(lowercase) disables Daisy, returnsdaisy removed
Daisy interleaving: In 16ch mode, the board alternates packets:
- Odd sample numbers (1,3,5...): channels 1-8 (main board)
- Even sample numbers (2,4,6...): channels 9-16 (Daisy)
Expect ~1:1 ratio of main:daisy packets. If Daisy packets are missing or all-zero, check that the Daisy board is firmly seated on the Cyton header pins.
ADS1299 Registers
Query with ?. Key registers per channel:
| Register | Default | Meaning |
|---|---|---|
0x68 |
Normal input, gain 24x, powered on | |
0xE8 |
Powered down (bit 7 set) | |
0x60 |
Normal input, gain 24x, SRB2 off |
BIAS_SENSP = 0xFF: All channels feeding bias drive (good)CONFIG1 = 0xB6: 250 Hz sample rate, daisy modeCONFIG3 = 0xEC: Internal reference, bias enabled
Electrode Quality Thresholds
| Std Dev (uV) | Status | Meaning |
|---|---|---|
| < 1 | FLAT | Shorted to reference or no contact |
| < 50 | CLEAN | Good signal, usable for all analysis |
| 50-100 | OK | Usable for most band power analysis |
| 100-200 | NOISY | May work for gross features (eye blinks) |
| > 200 | BAD CONTACT | Electrode touching but loose |
| mean ±187500 | RAILED | Not touching skin, pinned to ADC rail |
Session Persistence
The dongle does not persist the channel override across serial sessions. Every time you open a new serial connection, you must re-send 0xF0 0x02 <channel>. Keep the serial port open for the duration of your recording, or store the known channel and re-override on connect.
The board also goes to sleep after extended idle with no streaming. Toggle the power switch OFF→PC to wake it, then re-scan.
Dongle Switch Position
The dongle has a small switch with two positions:
| Position | Mode | Use |
|---|---|---|
| GPIO_6 | Normal operation | Use this for data streaming |
| Reset | Bootloader/programming | Firmware upload only |
If the switch is on "Reset", commands may partially work (radio config, v, ?) but binary streaming will fail — the RFDuino stays in bootloader mode and cannot relay continuous data. This is easy to miss because single-shot commands still get responses.
Troubleshooting
| Symptom | Cause | Fix |
|---|---|---|
| "Device failed to poll Host" | Channel mismatch | Use 0xF0 0x02 override scan (see above) |
| "System is Down" | Board off or wrong channel | Check power, scan channels |
| Channel stuck on set | 0x01 needs board handshake |
Use 0x02 override instead |
| RAILED at ±187500 uV | Electrode not connected | Check pin seating and wire |
| FLAT near 0 | Shorted to ref or no contact | Apply gel, press electrode |
| FLAT at exactly 0.0 | Daisy wires not plugged in | Check header pin connections |
| High noise (>200 uV std) | Poor electrode contact | Tighten cap, add paste |
0 packets after b |
Dongle switch on "Reset" | Set switch to GPIO_6 position |
| Commands work, stream doesn't | Dongle in bootloader mode | Check switch is GPIO_6, not Reset |
| Daisy ch all zero | Daisy not seated or C not sent |
Reseat Daisy, send C before b |
| All channels railed one side | Cap too loose / wrong size | Tighten straps, try gel electrodes |
| Commands work but stream doesn't | Board slept during idle | Toggle OFF→PC, re-pair |
Firmware Source
- Dongle:
github.com/OpenBCI/OpenBCI_Radios - Board:
github.com/OpenBCI/OpenBCI_32bit_Library