DPS-150 API

Python API and MCP server for the FNIRSI DPS-150 programmable DC power supply (0-24V, 0-5A).

Designed for automated testing workflows where an LLM (via MCP) or a Python script needs to control a bench power supply with built-in safety checks.

Files

File	Description
dps150.py	Python library + CLI — single-file DPS150 class wrapping all serial communication
dps150_mcp.py	MCP server — exposes the library as tools for Claude Code, Codex, Cursor, Amp, etc.
PROTOCOL.md	Full protocol specification reverse-engineered from the official FNIRSI Windows app
tests/	79 pytest tests covering protocol, library, and MCP layer — all serial I/O mocked, no device needed

Requirements

• uv (recommended) or Python 3.10+ with pip
• Dependencies are declared inline via PEP 723 script metadata — uv run installs them automatically

Command Line

Every function in the library is available as a CLI subcommand. Commands that set state (voltage, current, output on, protection thresholds, etc.) leave the device running — only read commands and sweeps turn the output off on exit.

# Device info
python dps150.py info
python dps150.py -p /dev/ttyACM0 info       # specify port

# Full state as JSON
python dps150.py state

# Read measurements
python dps150.py voltage
python dps150.py current
python dps150.py power
python dps150.py input-voltage
python dps150.py temperature

# Set voltage / current (does NOT enable output)
python dps150.py set-voltage 5.0
python dps150.py set-current 1.0

# Set voltage + current and turn output ON in one command
python dps150.py set-output 5.0 1.0

# Toggle output
python dps150.py on
python dps150.py off

# Protection thresholds
python dps150.py set-ovp 25.0
python dps150.py set-ocp 5.5
python dps150.py set-opp 130.0
python dps150.py set-otp 80.0
python dps150.py set-lvp 3.0

# Presets
python dps150.py presets
python dps150.py set-preset 1 3.3 0.5

# Display / sound
python dps150.py set-brightness 128
python dps150.py set-volume 5

# Metering (Ah/Wh counters)
python dps150.py start-metering
python dps150.py stop-metering

# Voltage sweep: 0→12V, 0.5V steps, 0.5s hold, 1A limit
python dps150.py sweep-voltage 0 12 0.5 0.5 1.0

# Current sweep: 0→3A, 0.1A steps, 0.5s hold, 5V fixed
python dps150.py sweep-current 0 3 0.1 0.5 5.0

# Enter firmware upgrade mode (WARNING: requires USB replug to recover)
python dps150.py dfu

The default port is /dev/cu.usbmodem065AD9D205B31. Override with -p PORT.

Python Library

from dps150 import DPS150

with DPS150("/dev/cu.usbmodemXXX") as psu:
    print(psu.model, psu.firmware_version)
    print(psu.read_state())

    # Set 5V at 1A and enable output
    psu.set_output(5.0, 1.0)

    # Read measurements
    print(f"{psu.read_voltage():.2f}V  {psu.read_current():.3f}A")

    # Voltage sweep: 0-12V in 0.5V steps, 1A limit, 0.5s per step
    results = psu.sweep_voltage(0, 12, 0.5, 0.5, 1.0)
    for r in results:
        print(f"  {r['voltage']:.2f}V  {r['current']:.3f}A  {r['power']:.2f}W")

Output is automatically turned off when the context manager exits (even on exceptions). Use psu.close() instead of psu.disconnect() if you want to detach without turning the output off.

MCP Server

Add to your MCP client config (Claude Code, Cursor, Amp, Codex, etc.):

{
  "mcpServers": {
    "dps150": {
      "command": "uv",
      "args": ["run", "/path/to/dps150_mcp.py"]
    }
  }
}

The server exposes these tools:

Tool	Description
connect(port)	Open session, read device info
disconnect()	Output off + close session
read_state()	Full state dump as JSON
set_voltage(volts)	Set voltage setpoint
set_current(amps)	Set current limit
set_output(volts, amps)	Set V/A then enable output
output_on() / output_off()	Toggle output
set_ovp(volts) / set_ocp(amps) / set_opp(watts)	Protection thresholds
sweep_voltage(start_v, stop_v, step_v, hold_s, current_limit)	Voltage sweep with readings
sweep_current(start_a, stop_a, step_a, hold_s, voltage)	Current sweep with readings

Safety

• All setters validate against the device's reported maximums (read on connect)
• Protection thresholds validate against the device's ceiling values
• set_output() always sets voltage and current before enabling
• disconnect() always turns the output off first
• Context manager __exit__ calls disconnect() even on exceptions
• Sweeps validate the full range before starting and turn output off when done
• CLI commands that set state use close() (output stays on); read-only commands and sweeps use disconnect() (output off)

Tests

79 tests covering protocol encoding (against PROTOCOL.md examples), validation, state parsing, telemetry, and the MCP tool layer. All serial I/O is mocked — no device needed.

just test

Protocol

See PROTOCOL.md for the full serial protocol specification, including packet structure, register map, command bytes, and data formats. All register addresses and offsets in the code reference sections from this document.