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E-Paper Refresh Lab

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About This MicroSim

An e-paper clock that shows minutes must update its screen 1,440 times a day. There are two ways to do it:

  • A full refresh flashes the whole screen between black and white before showing the new picture. It takes about 2 seconds and leaves a perfectly clean image.
  • A partial refresh changes only the pixels that need to change. It takes about 0.3 seconds and does not flash, but each one leaves a faint ghost of the old digits.

This lab uses a simple ghost model: every partial refresh adds 1.6 percent to the ghost level, and a full refresh resets it to zero. The preview shows the ghosts as faint copies of earlier times behind the current one, the meter shows the ghost level (above 50 percent the ghosts are easy to notice), and the timeline shows the last 120 refreshes with the ghost level drawn above them as a red sawtooth.

How to Use

  1. Choose a Refresh mode: always full, always partial, or mixed (a full refresh after every N partial refreshes).
  2. In mixed mode, set N with the slider.
  3. Press Advance one minute to step through refreshes one at a time. A full refresh shows a short black-and-white flash.
  4. Press Run a day to fast-forward 24 hours (1,440 updates). Press Pause to stop early.
  5. Read the counts, the total refresh time and the ghost level. Changing the mode or N starts a fresh test; Reset also starts over at 07:00.

Iframe Embed Code

You can add this MicroSim to any web page by adding this to your HTML:

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<iframe src="https://dmccreary.github.io/clocks-and-watches/sims/epaper-refresh-lab/main.html"
        height="537px"
        width="100%"
        scrolling="no"></iframe>

Lesson Plan

Grade Level

9-12 (Clocks and Watches with AI)

Duration

15 minutes

Prerequisites

  • Full and partial e-paper refresh and ghosting (Chapter 19)
  • The if partials >= 30 scheduling code in Chapter 19

Learning Objectives

Students will be able to:

  • Analyze how full and partial refresh strategies trade speed and flashing against ghosting
  • Calculate the total refresh time for a day from the counts of each refresh type
  • Evaluate a value of N that keeps ghosting below the noticeable level with the fewest flashes

Activities

  1. Three strategies (6 min): Run a full day in each mode (mixed with N = 30). Record the partial count, full count, total refresh time and final ghost level in a table.
  2. Check the math (3 min): For the mixed run, multiply the partial count by 0.3 s and the full count by 2.0 s. Does your total match the readout?
  3. Tune N (6 min): Find the largest N that never lets the ghost level reach the noticeable mark. Why might a real clock still choose a smaller N, or add a full refresh once an hour?

Assessment

  • The student explains why "always full" is the cleanest but slowest and most distracting choice.
  • The student explains why "always partial" eventually becomes unreadable.
  • The student justifies a value of N using the ghost meter and the flash count.

References

  1. Electronic paper - Wikipedia article on how e-paper particles move and why images persist.
  2. Screen burn-in and image persistence - Wikipedia article on ghost images left on displays.
  3. Waveshare e-Paper Driver HAT wiki - Notes on full and partial refresh for Waveshare panels.
  4. MicroPython framebuf module - The frame buffer used to prepare each e-paper image.