Analog bridge

Analog Bridge

A modular, open hardware 16-channel measurement and logic-monitoring platform built around an ATtiny3226 and four ADS1115 ADCs. The bridge exposes a line-oriented SCPI interface over Ethernet and USB serial, making it useful for automated test fixtures, digital logic observation, and lightweight data acquisition.

Status: Work in progress. The hardware, firmware, and host tools are under active development.

Features

• 16 single-ended analog inputs per device
• 3.3 V logic-level classification in the included monitor application
• Four ADS1115 converters on a shared I²C bus
• ATtiny3226-based firmware
• Ethernet connectivity through an ENC28J60
• USB-UART access at 115200 8N1
• SCPI commands for identification, channel configuration, status, and measurements
• Python web dashboards for live channel monitoring and oscilloscope-style plotting
• KiCad PCB and schematic sources
• 3D-printable enclosure plates and manufacturing files

Repository layout

analog-bridge/
├── analog-bridge-PCB/       # KiCad project, schematic, and PCB layout
├── analog-bridge/            # PlatformIO firmware and Python host tools
│   ├── src/                  # Firmware sources
│   ├── include/              # Firmware headers
│   ├── lib/                  # Project libraries
│   ├── test/                 # PlatformIO tests
│   ├── platformio.ini        # Build and upload configuration
│   ├── API_README.md         # Complete SCPI and transport reference
│   ├── analog_bridge_monitor.py
│   └── analog_bridge_oscilloscope.py
└── manufacturing/            # 3MF and SVG enclosure/manufacturing files

Channel mapping

Each ADS1115 contributes four single-ended inputs:

The firmware uses the ADS1115 GAIN_ONE setting, with a nominal input range of approximately ±4.096 V. Always observe the electrical limits of the ADC and the assembled hardware.

SCPI interface

The device accepts one command per line. Commands are case-insensitive and can be sent over either transport:

• Ethernet: DHCP, TCP port 5025
• USB serial: 115200 8N1

Example Ethernet session:

printf '*IDN?\n' | nc 192.168.1.42 5025
printf 'MEAS:RAW? 6\n' | nc 192.168.1.42 5025

Frequently used commands include:

Supported rates are 8, 16, 32, 64, 128, 250, 475, and 860 SPS. For the full command reference, wiring information, response formats, and transport details, see analog-bridge/API_README.md.

The SCPI interface has no authentication or encryption. Use Ethernet access only on a trusted network.

Firmware development

The firmware is built with PlatformIO and the Arduino framework.

Prerequisites

• PlatformIO Core or the PlatformIO IDE extension
• An ATtiny3226 UPDI programmer
• pymcuprog for UPDI upload:

python3 -m pip install pymcuprog

Build and upload

From the firmware directory:

cd analog-bridge
pio run
pio run -e Upload_UPDI -t upload

Configure the upload port and speed for your UPDI adapter according to your local setup. The default PlatformIO environment is Upload_UPDI.

ADC diagnostic firmware

The repository includes a direct ADC test firmware that bypasses the normal SCPI scheduler:

pio run -e ADC_TEST -t upload

Open the serial port at 115200 8N1 to view probe and raw conversion output. Use this mode to isolate ADC, I²C, power, address, or wiring problems.

Python host tools

The host applications use only the Python standard library unless USB serial discovery is needed.

Live channel monitor

The monitor discovers up to two bridges over Ethernet or USB serial and serves a live 32-channel dashboard. Ethernet discovery scans local IPv4 /24 networks for TCP port 5025; USB discovery requires pyserial.

cd analog-bridge
python3 -m pip install pyserial  # optional, required for USB discovery
python3 analog_bridge_monitor.py

Open http://127.0.0.1:8080. By default, channels are classified as:

• HIGH: ≥ 2.00 V
• LOW: ≤ 0.80 V
• doubt: between the two thresholds

Customize the thresholds, serial port, or web server:

python3 analog_bridge_monitor.py \
  --serial-port /dev/ttyUSB0 \
  --high 2.2 \
  --low 0.7 \
  --port 8080

Network oscilloscope

The oscilloscope discovers up to four Ethernet bridges and plots AIN0 from each ADS1115: logical channels 0, 4, 8, and 12.

python3 analog_bridge_oscilloscope.py

Open http://127.0.0.1:8090. Adjust the rolling history and polling interval with:

python3 analog_bridge_oscilloscope.py --history 60 --poll 0.1 --port 8090

The tools use the device’s millisecond timestamp, which is relative to device boot rather than synchronized Unix time.

Hardware sources

The KiCad project is in analog-bridge-PCB/. It includes the main PCB, project configuration, and analog-section schematic. Manufacturing and enclosure assets are in manufacturing/, including SVG and 3MF files.

The primary ATtiny3226 connections are:

Safety and limitations

• Verify input voltage, grounding, and signal integrity before connecting external equipment.
• The analog inputs are not isolated and the SCPI network service is unauthenticated.
• Measurement rates are per-channel scheduling targets; use returned timestamps to determine the achieved rate.
• Configuration is held in RAM and returns to the default state after reset or power loss.

Contributing

Issues and pull requests are welcome. When reporting a hardware or firmware problem, include the board revision, firmware environment, transport used, wiring, and relevant serial or SCPI output.

License

This project is licensed under the Open Community License v1.1 (OCL v1.1), without add-on conditions.

OCL v1.1 grants non-commercial users the right to use, copy, modify, and repair the project and requires distributed derivatives to remain under OCL. Commercial business use is limited to internal use unless a separate business or repair license is obtained. See LICENSE for the complete terms.

Third-party components and dependencies distributed with or alongside this project remain under their respective licenses where those licenses are incompatible with OCL. The authoritative OCL text and available add-ons are maintained by the OpenCommunityLicence project.