A visual timer for a classroom projector or OBS

The technique

Digits ask you to do a sum. You read 12:40, then work out what that means for the job in front of you. A shrinking disc skips that step. You see how much is left the way you see how much is left in a glass.

That matters most when lots of people share one clock. In a classroom, a timer on the projector answers ‘how long left?’ before anyone asks. On a study stream, people working along at home can see where the session is without asking in the chat.

What the research says

Judging time is harder with ADHD on average, at least in lab tests. A 2022 meta-analysis by Marx and colleagues pooled 55 studies comparing people with and without ADHD. People with ADHD had more trouble telling very short spans apart (especially under a second), and their guesses of spans lasting a few seconds varied more. Those spans are seconds long, a long way from a 20-minute reading block.

We looked for solid studies of visual timers themselves and didn’t find one we could check, so we aren’t claiming one. The case here is practical, and it’s ours: a visible timer saves everyone from doing the sum, and it gives the whole room the same edge to work towards.

On a projector

• Press Full screen to hide the browser and make the disc and digits bigger. Press it again, or Esc, to leave.
• Look at it from the back row before the lesson. The visual timer uses the look chosen in the focus timer in the same browser. If it’s faint, open Settings → Look and reading there and try Dark or More contrast.
• Give each timer one job and a label that says it, such as ‘Pack up’.
• The face is fixed, like a clock’s. Up to an hour, 10 minutes is always a sixth of the disc and 2 minutes is a thin slice. Longer timers use a two-hour face.
• While it runs, the page asks the computer to keep the screen on where the browser allows it, so the projector doesn’t fall asleep halfway through.
• At zero it plays a short, quiet chime if sound is on in the focus timer and someone has pressed something on the page. A timer started by the link alone stays silent. Either way, don’t count on the back row hearing it.
• When time’s up, the big button says Again, for another round of the same length.

It works at a desk too: prop a phone beside the homework and it keeps the screen on.

Try this week

Pick one thing you time often: packing up, silent reading or a study block on stream. Make its link (below), open it where people will see it and check it from where they’ll be: the back row or your stream preview. Save the link as a bookmark, so next time it’s one click. If it doesn’t suit the room, change the label or the length another day. If the week gets away from you, that’s fine too.

Links that set it up

The visual timer is at timer.logicfire.app/visual-timer. Pick a length from 1m to 2h, or type any whole number of minutes from 1 to 120 in Any length and press Set. Each length has its own address, such as timer.logicfire.app/visual-timer/25 for 25 minutes. Nothing is saved or sent and no sign-in is needed, which suits a shared school computer.

Add any of these after the length, starting with ? and joined with &:

• ‘start=1’ starts it as the page opens.
• ‘label=Reading’ shows what the time is for above the disc, up to 40 characters. Type %20 for a space: ‘label=Pack%20up’.
• ‘obs=1’ shows only the disc, the digits and the label, on a clear background.

A 10-minute pack-up timer for class: timer.logicfire.app/visual-timer/10?label=Pack%20up

In OBS Studio

Open your link in a normal browser first, without ‘obs=1’, to check the length and label. Then:

1. Under Sources, press + and choose Browser. Name it ‘Timer’ and add it.
2. In the window that opens, paste your link into URL, for example timer.logicfire.app/visual-timer/25?obs=1&start=1&label=Reading
3. Set Width to 800 and Height to 400 for the disc beside the digits, or 400 and 460 for the disc above them.
4. Tick Refresh browser when scene becomes active if you want it to start again from the full length whenever you switch to that scene. Press OK.
5. Drag its corners in the preview to size it. OBS has its own browser, so your usual look doesn’t carry over: check the digits over your real scene, and place it where they stand out.

Without the refresh box, it keeps time by the clock: switch away for a while and it still shows the right time when you return.

With ‘obs=1’ there are no buttons. To pause, right-click the source, choose Interact, click inside the window and press Space. Press Space again to carry on. R takes it back to the full length, ready for Space. Refresh cache of current page, in the source’s properties, starts it over.

OBS lets pages play sound without a press, so the chime can play at zero. To turn it down or mute it, tick Control audio via OBS in the source’s properties, then use the audio mixer.

For a study stream, try two scenes: one with a 25-minute timer and one with a 5-minute timer labelled ‘Break’, each with the refresh box ticked. Switching scenes starts each one fresh.