pmd-pycore

Python interface for ElmorLabs PMD power measurement devices (PMD2, PMD2X, PMD-USB).

Supported devices

PMD-USB (discontinued)	PMD2 (discontinued)	PMD2X (current)
4 channels (PCIE1, PCIE2, EPS1, EPS2) over a CH340 USB-serial bridge. No ATX24/motherboard rail, no 12VHPWR.	2x EPS, 3x PCIe, 1x ATX24, 1x 12VHPWR connector. STM32 USB-serial interface. Superseded by PMD2X.	Same rail set as PMD2, plus per-wire 12VHPWR monitoring and connector thermistors.

PMD-USB was superseded by PMD2, which was in turn superseded by PMD2X -- the only one of the three still sold. All three measure voltage/current/power on CPU, GPU, and (PMD2/PMD2X only) motherboard power cables, with an OLED display and USB connection to a PC for logging.

Pre-requisites

• Python >= 3.11, with pyserial (and numpy for the example scripts)
• PMD-USB uses a CH340 USB-serial chip. Linux has an in-kernel driver for it (binds automatically, nothing to install). Windows does not ship one -- if the device shows up in Device Manager but never gets a COM port, install the CH340/CH341 driver from the chip manufacturer's site (wch-ic.com, search "CH340"/"CH341") and replug. PMD2/PMD2X use an STM32 VCP instead and don't need a separate driver on either OS.

Install

pip install -r requirements.txt
pip install -e .

Usage

PMD2 / PMD2X

from pmd_pycore.core import (
    get_pmd2_ports,
    read_pmd2_welcome_string,
    read_pmd2_device,
    read_pmd2_uid,
    read_pmd2_sensors,
    translate_pmd2_sensor_struct,
)
import serial

port = get_pmd2_ports()[0]["port"]
ser = serial.Serial(port, 115200, timeout=1, rtscts=False, dsrdtr=False)

device_info = read_pmd2_device(ser)
sensors = read_pmd2_sensors(ser, device_info["ProductId"])
readings = translate_pmd2_sensor_struct(sensors, device_info["ProductId"])
print(readings["12V"])  # {'voltage': 12.0, 'current': 1.0, 'power': 12.0}

Currently implemented are the device's read-only commands: CMD_WELCOME (read_pmd2_welcome_string), CMD_READ_VENDOR_DATA (read_pmd2_device), CMD_READ_UID (read_pmd2_uid), and CMD_READ_SENSOR_VALUES (read_pmd2_sensors). Writing/action commands (continuous TX, config read/write, reset, bootloader) are not implemented.

See examples/read_sensors.py — a polling/averaging loop that mirrors the original sample script.

PMD-USB

PMD-USB is a different device family -- a CH340 USB-serial bridge rather than PMD2/PMD2X's STM32 VCP, with its own command set and a simpler sensor set (PCIE1, PCIE2, EPS1, EPS2 only; no ATX24 rails, no 12VHPWR). There's no firmware source for it, so this was ported from and verified against the reference implementations linked below plus a real device.

from pmd_pycore.core import get_pmdusb_ports, read_pmdusb_id, read_pmdusb_sensors, translate_pmdusb_sensors
import serial

port = get_pmdusb_ports()[0]["port"]
ser = serial.Serial(port, 115200, timeout=1)

device_info = read_pmdusb_id(ser)
sensors = read_pmdusb_sensors(ser)
readings = translate_pmdusb_sensors(sensors)
print(readings["EPS1"])  # {'voltage': 12.0, 'current': 1.0, 'power': 12.0}

Implemented: CMD_WELCOME (read_pmdusb_welcome_string), CMD_READ_ID (read_pmdusb_id), and CMD_READ_SENSOR_VALUES (read_pmdusb_sensors/translate_pmdusb_sensors). This command already returns calibrated readings -- confirmed against the official PMD-USB GUI app's source, which uses it directly with no client-side calibration math -- so CMD_READ_ADC's raw path isn't needed. translate_pmdusb_aggregate_power adds GPU/CPU/Total power (PCIE1+PCIE2 / EPS1+EPS2 / sum), computed client-side the same way the official app does; PMD-USB's firmware doesn't compute these on-device the way PMD2/PMD2X's does.

Note: PMD-USB has no per-unit UID/serial number anywhere -- not in the UART protocol (no command for it), and not at the USB level (the CH340 chip's serial number field reads empty on the device tested here). If you have more than one, there's no way to tell them apart besides which COM port they land on.

See KNOWN_LIMITATIONS.md for what's deliberately out of scope and why.

Examples

• examples/quickstart.py — connect to the first device found, trying PMD2/PMD2X first and falling back to PMD-USB, print its identity, and read sensor values once (for PMD2/PMD2X: per-rail readings, firmware-computed aggregate power, chip health, and PMD2X's 12VHPWR connector temperatures).
• examples/read_sensors.py — a polling/averaging loop, refreshing in place, for whichever device family is connected (same PMD2/PMD2X-first-then-PMD-USB detection as quickstart.py).

Status

This repository is under active development at ElmorLabs-P1/pmd-pycore. It provides an installable pmd_pycore package (serial discovery, UART command helpers, sensor structures, and readable-unit translation for the supported devices), a test suite, and CI for tests and tagged releases.

Tagged releases build an sdist/wheel and attach them to a GitHub Release. A PyPI-publish job is wired into the release workflow but not yet active -- it needs PyPI Trusted Publishing configured for this repo first (no credentials are stored in GitHub either way). Until that's set up, install from the GitHub Release assets or pip install -e . from a checkout.

Related repositories

• PMDLogger — C# reference implementation for PMD-USB (there's no public PMD-USB firmware source); PMD_USB_Device.cs has the command set and sensor scaling used here.
• PMD-USB — the official PMD-USB GUI app; FormPMD.cs confirmed CMD_READ_SENSOR_VALUES is already calibrated and has the CMD_READ_CONFIG struct layout.
• pmd-usb-serial-interface-fast / elmorlabs-pmd-usb-serial-interface — Python sample scripts for PMD-USB, cross-checked against PMDLogger and a real device.