psychopy-chronos 0.0.1

Driver for the PST Chronos response box

psychopy-chronos

Python driver for the PST Chronos response box, with a drop-in PsychoPy keyboard replacement.

Installation

pip install psychopy-chronos

Windows driver

Install the USB driver from the chronos_driver_win/ folder before first use if you never installed E-Prime on your machine.

Usage

Standalone

from chronos import Chronos

with Chronos() as box:
    events = box.get_events()

PsychoPy Builder

Add a Code Component with this in the Before Experiment tab:

from chronos import HybridKeyboard
from psychopy.hardware import keyboard
keyboard.Keyboard = HybridKeyboard

All Builder Keyboard Response components will then capture Chronos button presses alongside regular keyboard input. Buttons are coded '1' through '5' left to right, so add them to the allowed keys list in your Keyboard Response component.

To save hardware timestamps, add this to the End Routine tab:

if key_resp.response_log:
    thisExp.addData('chronos_hw_us',
        [getattr(k, 'hw_timestamp_us', '') for k in key_resp.response_log])
    thisExp.addData('chronos_pc_time_s',
        [getattr(k, 'tDown', '') for k in key_resp.response_log])

Hardware timestamps and drift correction

Each press is timestamped by both the host PC (chronos_pc_time_s, seconds from experiment start) and the Chronos internal crystal (chronos_hw_us, microseconds).

The crystal drifts relative to the PC clock. I measured +68.7ppm on my laptop (1001 presses over 685s, about 47ms of total drift). The drift is linear and correctable offline by regressing chronos_pc_time_s onto chronos_hw_us:

import numpy as np
slope, intercept = np.polyfit(hw_us_array, pc_time_array, 1)
corrected_rt = slope * hw_rt_us + intercept

Drift magnitude will vary across units. The test script used for this measurement is in test_chronos_timing.py.

chronos_hw_us is a 32-bit counter that wraps every 71.6 minutes. Use modulo 2^32 arithmetic for elapsed time calculations across long sessions.