axxpd 1.0.0

Python library for controlling AxxPD USB-C PD 3.1 EPR sink via SCPI

axxpd

Python library for controlling an AxxPD USB-C PD 3.1 EPR power source over its SCPI interface.

AxxPD is a programmable USB-C Power Delivery tool: it draws negotiated power from a USB-C PD charger (it is a PD sink) and re-exposes it as a controllable bench-supply output, from 3.3 V up to 48 V (up to 240 W), with voltage/current/power measurement, protection, and automation over a USB CDC serial port. This library wraps that SCPI command set as a Python API and auto-discovers the device's serial port.

Installation

pip install axxpd

Requires Python 3.8+ and pyserial (installed automatically).

Before you start

• AxxPD is a sink — plug a USB-C PD charger or power bank into its input.
• The output is off at boot; call output_on() to enable it.
• Voltages above 20 V (the EPR range, up to 48 V / 240 W) require both the charger and the cable to support EPR — use a 240 W e-marked USB-C cable. Without one you're capped around 20 V.
• The voltages you can actually reach depend on what the charger advertises; AxxPD requests the closest match and reports the contract it got.

⚠️ Safety: the output can reach 48 V at up to 240 W. Current-limit or disconnect your load before enabling the output, and set set_ocp() appropriately.

Quick start

from axxpd import AxxPD, AxxPDError

try:
    pd = AxxPD()                  # auto-detects the AxxPD serial port
except AxxPDError:
    pd = AxxPD("COM10")           # ...or pass the port explicitly

with pd:
    print(pd.idn())               # device identity
    pd.set_voltage(12.0, current=2.0)   # 12 V, 2 A current limit
    pd.output_on()

    m = pd.measure()              # dict: voltage, current, power, energy_wh,
                                  # charge_ah, temp_die, temp_ntc
    print(f"{m['voltage']:.3f} V, {m['current']:.3f} A")

    for sample in pd.stream(duration=10):   # ~20 Hz telemetry
        print(sample)

    pd.output_off()

All values are SI: volts, amps, watts, energy in Wh, charge in Ah, temperature in °C (or °F if the device's Fahrenheit setting is on).

Connecting

Auto-detect picks the STMicroelectronics Virtual COM Port (VID:PID 0483:5740) — not the ST-Link debug port. If no device is found, AxxPD() raises AxxPDError; pass the port explicitly instead. Ports look like COM10 on Windows, /dev/ttyACM0 on Linux, or /dev/cu.usbmodem* on macOS. To list candidates:

from serial.tools import list_ports
for p in list_ports.comports():
    print(p.device, p.description)

All library errors (connection failure, unparseable device response) raise AxxPDError, so wrap calls in try/except AxxPDError for robust automation.

A few terms

A PD charger advertises one or more PDOs (selectable voltage/current offerings); the sink negotiates one, forming a contract. PPS and AVS are adjustable-voltage modes; EPR (Extended Power Range) unlocks voltages above 20 V, up to 48 V / 240 W.

API overview

• Identity / system: idn(), reset(), reboot(), selftest()
• Output: output_on(), output_off(), output_state()
• Set point: set_voltage(v, current=None), set_pps(v, current=None), set_avs(v), set_pdo(index), set_mode(mode)
• PD info: list_pdos(), list_all_pdos(), contract(), enter_epr(), exit_epr()
• Measurement: measure(), measure_voltage(), measure_current(), measure_power(), measure_temperature(), measure_energy()
• Protection: set_ocp(amps), set_ovp(volts), protection_status(), protection_clear()
• Sequencing: seq_add(v, time_ms), seq_clear(), seq_list(), seq_run(), seq_stop()
• Streaming: stream(duration=None, callback=None) — yields telemetry dicts at ~20 Hz (omit duration to stream until interrupted)
• Errors: every library error raises AxxPDError

stream() skips malformed frames silently, so the sample count over a fixed duration isn't guaranteed. set_voltage() does not raise if the source can't satisfy the request — it falls back to the nearest PDO, so confirm with measure() or contract().

Troubleshooting

Symptom	Likely cause
AxxPDError on connect / wrong port	Device not enumerated, or the ST-Link port was picked — pass the port explicitly
Reads 0 V	Output not enabled (output_on()), no PD source connected, or no contract — check contract() and output_state()
Can't reach voltages above 20 V	No EPR — use a 240 W e-marked cable and a charger that advertises EPR

For the full SCPI command reference and device documentation, see the project repository.

License

GPL-3.0-only. Copyright Axel Johansson.