4 layers50 × 50 mm Chua x7r, the printed circuit board in 3D

Chua x7r

Q: How big is the Chua x7r PCB?

It measures 50 × 50 mm and has 4 copper layers, 1.6 mm thick.

Q: What parts does the Chua x7r use?

17 parts, built around the TL072 and MMBF4118. The full list of its parts is on this page, with links to each part's symbol and footprint where PCBKit's library has them.

Q: Where can I download the Chua x7r KiCad files?

From the heurstc/Chua-memcapacitor repository on GitHub, at the commit this page was made from: the board is kicad/chua_x7r.kicad_pcb and its schematic kicad/chua_x7r.kicad_sch. PCBKit opens the board in the browser, with nothing to install.

Q: Can I use the Chua x7r design in my own project?

Its repository states no licence, so its author keeps all rights: ask heurstc before reusing the design.

heurstc/Chua-memcapacitor

5D chaos monitor: XIAO RP2350 + ADS1262 streaming Chua attractor data at 12kHz/ch over USB CDC to Linux

Full screen GitHub .kicad_pcb

Size: 50 × 50 mm
Copper layers: 4
Thickness: 1.6 mm
Parts: 17
Nets: 12
Pads: 41
Tracks, vias: 53, 17
Pours: 3
Routed: Yes
KiCad: KiCad 7 (file 20221018)
Created: 7 Aug 2026
Updated: 10 Aug 2026

Overview

Chua x7r is an open-source printed circuit board by heurstc, from the heurstc/Chua-memcapacitor repository on GitHub. It is a 4-layer board of 50 × 50 mm with 17 parts on 12 nets, routed with 53 tracks and 17 vias.

It is built around the TL072 and MMBF4118. Its parts include 10 resistors, 4 capacitors, 1 IC, 1 transistor and 1 inductor. It belongs with the computers and single-board computers boards of this library.

Main components

README

README.md

Chua-memcapacitor — 5D Chaos Monitor

Real-time acquisition and visualisation of a 5-dimensional chaotic attractor using a Seeed Studio XIAO RP2350 and two ADS1262 32-bit ADCs, streaming to Linux at 12 kHz per channel over USB CDC.

System Overview

text

Chua Circuit (±8 V)
  │
  ▼
Signal Conditioning Board  (×5 channels)
  │  R_IN 1kΩ → ±9V clamp → TL072-A input buffer
  │  → ÷4 attenuator (30k/10k) → TL072-B divider buffer
  │  → Sallen-Key 2nd-order Butterworth LPF @ 4.95 kHz
  │  → ±2.5V clamp → ADS_CHn
  ▼
XIAO RP2350
  │  Core 1: tight-poll SPI sampling (ADS1262 × 2)
  │  Core 0: USB CDC packetiser (14-byte frames, XOR checksum)
  ▼
Linux Host  /dev/ttyACM0
  │  capture.py  — packet parser, drop/error stats
  │  buffer.py   — lock-free circular numpy buffers
  │  plotter.py  — real-time 3D attractor + 2D projections
  ▼
matplotlib FuncAnimation @ 30 Hz

Hardware

Part	Role
Seeed XIAO RP2350	Dual-core Cortex-M33 MCU, USB FS CDC
ADS1262 × 2	32-bit delta-sigma ADC, 38,400 SPS max
TL072 × 8	Signal conditioning op-amps (SOIC-8)
BAT54 Schottky × 20	Input (±9V) and output (±2.5V) clamps
R 0402, C 0402 C0G	Divider and Sallen-Key filter passives

Channel mapping:

Channel	Chua variable	ADC
CH0	x	ADS1262-0 AIN0
CH1	y	ADS1262-0 AIN1
CH2	z	ADS1262-0 AIN2
CH3	w	ADS1262-1 AIN0
CH4	v	ADS1262-1 AIN1

SPI0 pin assignments (RP2350):

Signal	GPIO
SCK	GP6
MOSI	GP7
MISO	GP4
ADC0 CS / DRDY / RST	GP5 / GP0 / GP1
ADC1 CS / DRDY / RST	GP3 / GP2 / GP28

Signal Conditioning (Rev 2)

Each of the 5 channels uses a 3-op-amp topology:

text

Chua ──[R_IN 1kΩ]──[±9V clamp]──[TL072-A]──[÷4]──[TL072-B]──[SK LPF]──[TL072-C]──[±2.5V clamp]──► ADS1262

TL072-A — unity-gain input buffer; isolates Chua source impedance
÷4 attenuator — 30kΩ/10kΩ voltage divider; maps ±8V Chua → ±2V
TL072-B — unity-gain divider buffer; eliminates 7.5kΩ Thevenin source loading that would shift the filter cutoff from 4.95 kHz to 3.74 kHz
Sallen-Key LPF — 2nd-order Butterworth, fn = 4.95 kHz, Q = 0.731; R1=R2=10kΩ, C_FB=2.2nF C0G, C_SH=4.7nF C0G
TL072-C — SK active element / output buffer
±2.5V clamp — BAT54 Schottky protecting ADS1262 AVDD/AVSS rails

IC count: 15 TL072 units → 8 SOIC-8 packages (U1–U8, U8B spare).

Firmware

Built with the Pico SDK and TinyUSB.

text

firmware/
├── CMakeLists.txt
└── src/
    ├── ads1262.h / .c      ADS1262 SPI driver
    ├── ring_buffer.h       Lock-free SPSC ring buffer (4096 samples, ARM DMB)
    ├── sampler.h / .c      Core 1 entry — tight-poll sampling loop
    ├── main.c              Core 0 — USB CDC packetiser
    ├── tusb_config.h       TinyUSB configuration
    └── usb_descriptors.c   CDC descriptor

ADS1262 configuration:

Data rate: 38,400 SPS, filter: SINC1 (mandatory for single-cycle mux settling)
PGA bypassed; internal 2.5V reference

USB packet format (14 bytes):

text

[0xAD][0xC0][ch][seq_lo][seq_hi][ts0][ts1][ts2][ts3][val0][val1][val2][val3][XOR]
  sync         chan  seq (LE16)    timestamp µs (LE32)  value (LE32)   checksum

Build:

bash

mkdir firmware/build && cd firmware/build
cmake .. -DPICO_BOARD=seeed_xiao_rp2350
make -j$(nproc)
# flash: hold BOOT, connect USB, copy .uf2 to RPI-RP2 drive

Host Software

text

host/
├── capture.py    PacketParser — serial reader thread, sync/checksum/drop detection
├── buffer.py     ChannelBuffer — circular numpy arrays; SampleStore for 5 channels
├── plotter.py    FuncAnimation plots: 3D attractor, xy/xz projections, time series
└── main.py       Entry point — fanout thread, optional CSV logging

Install dependencies:

bash

pip install -r host/requirements.txt

Run:

bash

python3 host/main.py /dev/ttyACM0
# options:
#   --fps 30        animation frame rate
#   --trail 10000   number of points in attractor trail
#   --save FILE     log raw samples to CSV

The plotter opens a live window showing:

Left: 3D x/y/z attractor trajectory
Top centre: x–y phase portrait
Top right: x–z phase portrait
Bottom centre: w–v projection
Bottom right: per-channel time series + sample rate / error stats

SPICE Simulation

text

spice/
├── signal_cond.spice    ngspice netlist (BAT54 + TL072 behavioral models)
├── plot_response.py     scipy Bode / step / pole-zero plots
└── run_ngspice.sh       run simulation + plot (falls back to scipy-only if no ngspice)

bash

cd spice
./run_ngspice.sh

Produces ac_bode.dat, tran_1k.dat, tran_8k.dat, tran_step.dat and a Bode plot PNG.

KiCad Schematic

text

kicad/
├── gen_schematic.py              Python generator — run to rebuild .kicad_sch
├── signal_conditioning.kicad_sch KiCad 7 schematic (A2, 5 channels)
├── signal_conditioning.kicad_pro KiCad project file
└── bom.csv                       Bill of materials

To regenerate the schematic after editing the generator:

bash

python3 kicad/gen_schematic.py

Open signal_conditioning.kicad_sch directly in KiCad 7.

Throughput Budget

Parameter	Value
Channels	5
Effective SPS per channel	~12,800 (CH0–2) / ~19,200 (CH3–4)
Packet size	14 bytes
Raw USB data rate	~840 kB/s
USB FS CDC practical limit	~1 MB/s

License

MIT

Category and platform

Computers and single-board computers

Project files

Show this board on your page

https://pcbkit.io/boards/heurstc/Chua-memcapacitor

The board's own page, for a message or a post.

Source

Repository: heurstc/Chua-memcapacitor
Board file: kicad/chua_x7r.kicad_pcb
Commit: 582dafb
Licence: Not stated

Parts

Qty	Value	Footprint	References
2	18k	Resistor_SMD:R_0402_1005Metric	R3, R6
2	22k	Resistor_SMD:R_0402_1005Metric	R2, R5
2	3.3k	Resistor_SMD:R_0402_1005Metric	R1, R4
1	1.8k	Resistor_SMD:R_0402_1005Metric	R7
1	100nF	Capacitor_SMD:C_0402_1005Metric	C3
1	100nF X7R	Capacitor_SMD:C_0402_1005Metric	C2
1	10nF X7R	Capacitor_SMD:C_0402_1005Metric	C1
1	12R	Resistor_SMD:R_0402_1005Metric	R8
1	18mH	Inductor_SMD:L_Bourns_SRR1260	L1
1	1M	Resistor_SMD:R_0402_1005Metric	R9
1	47k	Resistor_SMD:R_0402_1005Metric	R10
1	47pF C0G	Capacitor_SMD:C_0402_1005Metric	C4
1	MMBF4118	Package_TO_SOT_SMD:SOT-23	Q1
1	TL072	Package_SO:SOIC-8_3.9x4.9mm_P1.27mm	U1

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Questions

How big is the Chua x7r PCB?

It measures 50 × 50 mm and has 4 copper layers, 1.6 mm thick.

What parts does the Chua x7r use?

17 parts, built around the TL072 and MMBF4118. The full list of its parts is on this page, with links to each part's symbol and footprint where PCBKit's library has them.

Where can I download the Chua x7r KiCad files?

From the heurstc/Chua-memcapacitor repository on GitHub, at the commit this page was made from: the board is kicad/chua_x7r.kicad_pcb and its schematic kicad/chua_x7r.kicad_sch. PCBKit opens the board in the browser, with nothing to install.

Can I use the Chua x7r design in my own project?

Its repository states no licence, so its author keeps all rights: ask heurstc before reusing the design.