keithley2400 0.1.1

Simple library for Keithley 2400 Source Measure Unit (SMU) control over RS-232/USB-serial

keithley2400

Simple, clean Python library for controlling the Keithley 2400 Source Measure Unit (SMU) over RS-232 / USB-serial.

Features

• Full V/I/R sourcing and measurement control via SCPI
• Pure-Python — no National Instruments VISA required
• Works natively on macOS (including Apple Silicon M1/M2/M3/M4), Linux, and Windows
• Statistical sampling with mean and standard deviation
• Generator-based voltage sweep (sweep_iv) for IV curves
• One-liner convenience function: quick_iv_sweep()
• Context manager support for safe resource cleanup
• Serial port discovery helper: find_serial_port()
• Automatic Keithley 2400 port discovery via *IDN? probing when resource=None or when a stale configured port fails

Installation

pip install keithley2400

Requirements

• Python 3.6+
• pyvisa >= 1.11.0
• pyvisa-py >= 0.5.2
• pyserial >= 3.4

Hardware Setup

The Keithley 2400 communicates over RS-232 using a USB-serial adapter.

1. Connect the USB-serial cable between the instrument's RS-232 port and your computer.
2. Ensure the instrument's baud rate matches (factory default: 9600 baud, 8N1).
3. Find your port:

from keithley2400 import find_serial_port
ports = find_serial_port()
# Example output: ['ASRL/dev/cu.usbserial-FTRTKC3X::INSTR']

Quick Start

1. Connect automatically (recommended)

from keithley2400 import Keithley2400

with Keithley2400(resource=None) as k:   # auto-discovers by probing *IDN?
    print(k.idn())

2. Find your serial port manually

from keithley2400 import find_serial_port
print(find_serial_port())

3. Run an IV Sweep (one-liner)

from keithley2400 import quick_iv_sweep

voltages = [v * 0.5 for v in range(0, 21)]  # 0 to 10 V in 0.5 V steps

csv_file = quick_iv_sweep(
    voltages=voltages,
    out_csv="iv_curve.csv",
    compliance_amps=0.01,    # 10 mA current limit
    stabilize_s=0.5,         # wait 500 ms after each voltage step
    n_samples=50,            # average 50 readings per point
)
print(f"Saved: {csv_file}")

4. Full Manual Control

from keithley2400 import Keithley2400

# Using context manager (automatically turns output off and closes on exit)
with Keithley2400(resource="ASRL/dev/cu.usbserial-FTRTKC3X::INSTR") as k:
    print(k.idn())

    k.set_source_v(5.0)
    k.set_current_compliance(0.01)  # 10 mA limit
    k.configure_measure_vi()
    k.output_on()

    v, i = k.read_v_i()
    print(f"V={v:.4f} V  I={i:.6e} A")

    # Statistical sampling
    stats = k.sample_stats(param="I", n=100, delay_s=0.01, stabilize_s=0.5)
    print(f"I mean={stats['mean']:.6e} A  stdev={stats['stdev']:.2e} A")

5. Resistance Measurement

from keithley2400 import Keithley2400

with Keithley2400() as k:
    # 2-wire resistance
    k.configure_measure_ohms(method="2W")
    k.set_ohms_source_current(1e-3)  # 1 mA test current
    k.output_on()
    r = k.read_r(mode="ohms")
    print(f"R = {r:.2f} Ohm")

6. Custom IV Sweep with Generator

from keithley2400 import Keithley2400
import csv

voltages = [round(v * 0.1, 2) for v in range(0, 101)]  # 0 to 10 V

with Keithley2400() as k:
    k.output_on()
    with open("iv_data.csv", "w", newline="") as f:
        writer = csv.writer(f)
        writer.writerow(["V_set", "I_mean_A", "I_stdev_A"])
        for v, i_mean, i_stdev in k.sweep_iv(voltages, compliance_amps=0.05):
            writer.writerow([v, i_mean, i_stdev])
            print(f"V={v:.2f}  I={i_mean:.4e} A")

API Reference

Keithley2400 Class

__init__(resource, backend="@py", settings=None)

Open connection to the instrument.

Parameter	Type	Default	Description
resource	str or None	None	PyVISA resource string. None or "auto" triggers auto-discovery by probing serial ports with *IDN?.
backend	str	"@py"	PyVISA backend ("@py" = pyvisa-py, no NI-VISA needed)
settings	SerialSettings	None	RS-232 parameters (default: 9600 8N1)

Output Control

Method	Description
output_on()	Enable source output
output_off()	Disable source output

Source Configuration

Method	Description
set_source_v(volts)	Source a voltage
set_source_i(amps)	Source a current
set_current_compliance(amps)	Set current limit (when sourcing V)
set_voltage_compliance(volts)	Set voltage limit (when sourcing I)

Measurement Configuration

Method	Description
configure_measure_vi(auto_range=True)	Measure V and I simultaneously
configure_measure_ohms(method="2W")	Resistance measurement (2W or 4W)
set_current_range(amps)	Manual current measurement range

Readings

Method	Returns	Description
read_v_i()	(float, float)	Voltage and current
read_v()	float	Voltage only
read_i()	float	Current only
read_r(mode="calc")	float	Resistance (R=V/I or instrument ohms)

Statistical Sampling

Method	Returns	Description
sample_stats(param, n=50, delay_s=0.01, stabilize_s=0.0)	dict	Mean and stdev over N readings

Returns: {"mean": float, "stdev": float, "n": float}

IV Sweep

Method	Returns	Description
sweep_iv(voltages, ...)	Iterator[(V, I_mean, I_stdev)]	Voltage sweep generator

Utilities

Method	Returns	Description
idn()	str	Instrument identification string
get_error()	str	Error queue query
close()	—	Close VISA session

SerialSettings Dataclass

Field	Default	Description
baud_rate	9600	Communication speed
data_bits	8	Data bits per character
parity	none	Parity check
stop_bits	one	Stop bits
terminator	"\r"	Line terminator (CR confirmed working)
timeout_ms	5000	Read timeout in milliseconds

Convenience Functions

find_serial_port(backend="@py") -> list

List all detected USB-serial ports.

find_keithley_resource(backend="@py", settings=None, verbose=True) -> Optional[str]

Probe detected serial ports with *IDN? and return the first one that identifies as a Keithley 2400.

quick_iv_sweep(voltages, out_csv=None, resource=..., ...) -> Optional[str]

One-liner: connect → sweep → save CSV → disconnect. Returns the CSV path.

CSV Output Format

voltage_V,current_mean_A,current_stdev_A,n_samples
0.0,+1.234567e-09,2.345e-11,50
0.5,+5.678901e-09,3.456e-11,50
1.0,+1.234567e-08,4.567e-11,50
...

Notes

• Always call output_off() before close() (the context manager does this automatically)
• FORM:ELEM VOLT,CURR is set in initialize() — this makes read_v_i() parsing deterministic
• If you switch to configure_measure_ohms(), FORM:ELEM changes to RES; call configure_measure_vi() again to switch back
• If a configured serial port goes stale, Keithley2400(..., auto_discover=True) will scan candidate serial ports and accept only one whose *IDN? response looks like a Keithley 2400
• The @py backend works without a NI-VISA installation — fully compatible with Apple Silicon

License

MIT License