What Is an Operator Interface

What Is an Operator Interface for Manufacturing Test

An operator interface is the screen a production floor worker sees when running a test. It handles serial number entry, displays pass/fail results, shows prompts for manual steps, and logs everything without the operator touching code. This guide covers what an operator interface should include, how the major test frameworks handle it, and how to set one up with OpenHTF and TofuPilot.

Why Operators Need a Dedicated Interface

Test engineers write Python scripts. Operators run them. These are different jobs with different needs.

Running a test from a terminal works during development. In production, the operator needs a purpose-built screen that removes complexity and prevents mistakes.

What an Operator Interface Should Include

How Test Frameworks Handle Operator Interfaces

NI TestStand

TestStand ships with pre-built operator interfaces in LabVIEW, C#, and VB.NET. The source code is provided so you can customize it. It supports user roles (operator, developer, admin), concurrent test executions, and report generation.

Strengths: Mature, full-featured, customizable. Weaknesses: Requires a TestStand license ($3-5K per seat), Windows only, tied to the NI ecosystem.

OpenTAP

OpenTAP offers an operator panel plugin that provides a simplified view for running test plans. It includes a "focus mode" that minimizes interactions to start/stop and pass/fail.

Strengths: Open source core, cross-platform. Weaknesses: .NET ecosystem, sparse documentation, basic operator UI.

OpenHTF

OpenHTF includes a built-in Station Server that serves a web interface at localhost:12000. It shows test status, phase progress, and handles operator prompts through the browser.

Strengths: Web-based (works on any device with a browser), no installation needed on the operator's machine. Weaknesses: The built-in UI is minimal. For production use, most teams pair OpenHTF with a dedicated frontend.

pytest with HardPy

HardPy adds a browser-based operator panel to pytest. It shows test hierarchy, dialog boxes for operator input, and real-time charts.

Strengths: pytest-native, modern web UI. Weaknesses: New project, limited adoption, basic feature set.

Comparison Table

Prerequisites

• Python 3.10+
• OpenHTF installed (pip install openhtf)
• TofuPilot Python SDK installed (pip install tofupilot)

Step 1: Add Operator Prompts to Your Test

OpenHTF handles operator interaction through prompts. The operator sees a message and optionally provides input before the test continues.

import openhtf as htf
from openhtf.plugs import user_input


@htf.plug(prompts=user_input.UserInput)
def phase_visual_inspection(test, prompts):
    """Ask the operator to perform a visual check."""
    prompts.prompt(
        "Inspect the board for solder bridges or missing components. "
        "Press Enter when done."
    )


@htf.plug(prompts=user_input.UserInput)
@htf.measures(
    htf.Measurement("operator_serial").with_args(docstring="Scanned serial number"),
)
def phase_scan_serial(test, prompts):
    """Prompt the operator to scan the DUT serial number."""
    serial = prompts.prompt(
        "Scan the barcode on the DUT label.",
        text_input=True,
    )
    test.measurements.operator_serial = serial

Step 2: Stream to TofuPilot Operator UI

TofuPilot provides a web-based operator interface that streams test progress in real time. The operator sees prompts, measurements, and pass/fail results in a browser. No terminal, no code.

from tofupilot.openhtf import TofuPilot

test = htf.Test(
    phase_scan_serial,
    phase_visual_inspection,
)

with TofuPilot(test):
    test.execute(test_start=lambda: input("Scan serial: "))

When the test runs, TofuPilot streams the interface to a URL the operator can open on any device. The console prints the URL automatically.

Step 3: Deploy for Production

For production use, set up the operator station so the browser opens automatically in full-screen mode:

The operator's workflow becomes: scan barcode, follow prompts, see pass/fail. No terminal, no file system, no Python knowledge required.

Choosing the Right Approach