Day of the week clock
Let’s say we want to create a clock which doesn’t show the time of day, but instead which day of the week it is.
We could of course design an electronic timer circuit or write a computer program or App to do this. But my aim here is to do something really simple, something that anyone can do.
So this is my solution:
The basic hardware setup is a clock, powered by an external supply (not batteries) coupled to a timer unit that controls the supply being either off or on according to pre-set time window. With this we can repeatdly switch the clock off and back on, to slow it down so that instead of one revolution of the hour hand taking 12 hours, it would take 1 week. (We need to change the face of the clock too).
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A suitable control unit is one of those timer devices for heating systems as shown below. This can be programmed to be on, and off with different settings every day of the week.
To make the hour hand of the normal clock go one circle in 7 days rather than 12 hours, we need to introduce an on/off duty cycle to the clock of the ratio 1:14 (i.e. seven days times 2, as the clock normally does two revolutions each day).
If the granularity of the timer was in minutes, then it would to be set to be off for 24 x 60/14 = 27.428.. minutes each day. Clearly this can’t be set, unless we rounded down to 27 minutes, but then the clock wouldn’t be too accurate. A way around this is to set the timer for slightly different lengths each day over seven days.
One day is equal to 24 x 60 = 1440 minutes.
Therefore to achieve a week calendar, we need to switch the clock on for 1440 minutes over a seven day period.
We can achieve the this with two days with ‘on’ set for 3 hours 25 minutes and for the other five days, set ‘on’ for 3 hours 26 minutes (total 180 minutes). Example below.
Note the ‘on’ time can be set to happen in the middle of the night so the clock hand moves when (probably) everyone’s asleep and is static during the daytime pointing to the day of the week.
Now we have our clock..
