multicomp-mcp

MCP server for the Multicomp Pro MP711134 bench power supply with built-in multimeter (a rebadged OWON SPM-series source measuring unit), connected over USB serial. It lets an LLM agent control the PSU during live debugging sessions — e.g. power-cycling a board, watching its current profile during boot, or waiting for a rail to come up — without having to poll.

Tools

Setup

Requires uv. From this directory the server is already wired up via .mcp.json for Claude Code. To register it globally:

claude mcp add multicomp --scope user -- \
  uv run --project /path/to/multicomp-mcp multicomp-mcp

Configuration via environment variables:

• MULTICOMP_PORT — serial device path, overrides auto-discovery

• MULTICOMP_BAUD — baud rate (default 115200)

Without MULTICOMP_PORT the server discovers the instrument by enumerating USB serial ports, trying CH340 adapters (1a86:7523 — the bridge chip the MP711134 uses, which exposes no product string or serial number) first, and confirming with an *IDN? probe. Other serial devices on the bus are left alone unless the PSU isn't found, in which case they receive one harmless *IDN? query.

Protocol notes (verified on live hardware, firmware FV:V2.0.0)

The official command reference is the OWON SPM Series programming manual. Findings from probing the real device:

• 115200 baud 8N1, \n-terminated. Queries answer in ~10–20 ms.

• Set commands are silent on success and reply ERR on rejection (out-of-range value, unknown command). No SYST:ERR? queue to speak of (it always reads 0x0000).

• *IDN? → multicomp pro,MP711134,25280364,FV:V2.0.0

• PSU: VOLT, CURR, OUTP {ON|OFF}, VOLT:LIM (OVP), CURR:LIM (OCP), MEAS:VOLT?, MEAS:CURR?, MEAS:POW?

• MEAS:ALL:INFO? → V,I,P,OVP,OCP,OTP,mode (mode: 0 standby, 1 CV, 2 CC, 3 failure) — the workhorse status/poll query.

• MEAS:ALL? returns only V,I on this firmware (manual claims V I P).

• DMM readings come from CONF:ALL? → FUNC,value+unit,Auto|Manual,range (e.g. VOLT:DC,+0.0007V,AUTO,2V, RES,OL,AUTO,200k Ohm). MEAS:* always refers to the PSU output terminals, not the DMM.

• DMM function switch: FUNC:VOLT:DC, FUNC:VOLT:AC, FUNC:CURR:DC, FUNC:CURR:AC, FUNC:RES, FUNC:CAP, FUNC:DIOD, FUNC:CONT — takes ~0.8 s to apply. Ranging: VOLT:DC:RANG {200E-3|2|20|200|1000}, ...:RANG:AUTO {ON|OFF}, ...:RANG:NULL (relative mode); similar for CURR/RES.

• Compound commands (;-separated) are not supported — first command only.

• After OUTP ON the output ramps to the setpoint over ~1–2 s (no-load). Dropping the setpoint with no load is also slow (output caps discharge).

• The device occasionally drops a query sent immediately after a state change — the client retries empty reads.

• No sequencer/list mode over SCPI: every LIST/PROG/SEQ/TIMER style command returns ERR (the "waveform" feature in the marketing blurb is the on-screen V/I curve display). run_profile therefore drives the setpoint from the host.

• Do not flood the port: back-to-back writes with no gap wedge the instrument for several seconds (it stops answering). With ≥5 ms between transactions, sustained set+measure cycles at ~20-40 Hz are 100% reliable.

• Output slew (no load): ~5.5 V/s rising; falling is load-dependent — unloaded it droops at ~2 V/s, so downward steps need a real load to be meaningful.

• Quirks: SIM:KEY:* emulates front-panel keys; *RST is a factory reset (avoid); SYST:LOC returns control to the front panel.