Hi,
this is far from ideal, but it does something in the lines of what you want.
First you create a Databin and make that publicly available:
binstarttime = CreateDatabin[];
SetOptions[binstarttime, "Permissions" -> "Public"];
The data bin will have a short ID something like 4LilXAIZ; you obviously need to change that to your Databin's ID. This following command sets the count-down to 5 minutes:
DatabinAdd[Databin["4LilXAIZ"], {Now, Quantity[5, "Minutes"]}];
On each of the clients you run:
RunScheduledTask[dummy = Databin["4LilXAIZ"]["Latest"]["Data"];, 1];
Dynamic[Refresh[
If[dummy === {0, 0}, "Stop",
If[QuantityMagnitude[
UnitConvert[dummy[[2]], "Seconds"] -
UnitConvert[Now - dummy[[1]], "Seconds"]] < 0, "Time's up!",
UnitConvert[dummy[[2]], "Seconds"] -
UnitConvert[Now - dummy[[1]], "Seconds"]]],
UpdateInterval -> 0.01]]
That should initiate the countdown. If you or anyone wants to stop the countdown this works:
Quiet[DatabinAdd[Databin["4LilXAIZ"], {0, 0}];]
When you are done you should also remove the Scheduled task:
RemoveScheduledTask[ScheduledTasks[]]
This is, of course, not really optimal. The RunScheduledTask slows the display of the count-down down. (That sounds funny!). Anyway, I cannot improve it any further right now as I am invigilating an exam and we are nearly doneĀ
Cheers,
Marco
PS: If you can live with "distributing" a potential "Stop" with up to five seconds delay, this would work instead of the RunScheduledTask above:
RunScheduledTask[dummy = Databin["4LilXAIZ"]["Latest"]["Data"];, 5]
Then, the clock is much smoother and only stalls a bit every 5 seconds.
