Well, it’s been a minute.
I’ve been working on a pretty complex topic,
and in the meantime I need to think of something quick.
If only I had more time…
that’s it!
How ‘bout a little taste of November in January?
Do you have an electrical thing you want to have turn on at a specific time every day
and then also turn off at a specific time every day?
I know, so do I!
But that sounds really hard.
I mean, we all know how to make and break electrical connections with a switch -
you just gotta touch the metal together and then pull it apart real fast!
And we also have these clock things that have an hour hand that slowly turns in a circle twice a day.
But y’know…
some of ‘em only rotate once a day for those that prefer their time served that way.
I wonder if we could connect the technology of clocks with switches.
Oh look, it’s a that!
OK, like a door that’s left its frame,
that intro was unhinged.
I’m sure you’ve seen these things before, they’ve been around for a long time.
In fact, I’m not even sure how long they’ve been around.
Thanks to that Nintendo thing all the youngin’s are playing with
internet searches involving the word “switch” are ruined.
Now, I found a time switch from 1921 which automatically turns stairway lights off after three minutes,
but that’s not what I want to talk about here.
I want to talk about ordinary timer switches:
the kind where you tell it an on and off time and it repeats that daily.
I suppose this is a sufficiently obvious idea that it got implemented in one way or another
just as soon as we figured out the light bulb.
All we really need is a clock that can actuate a switch.
In theory this could be as simple as a rotary switch which gets hit by the hand of an ordinary wind-up clock.
When it collides with the switch, it would turn it from off to on and back.
To make this a little more flexible, instead of giving that clock hands
we can use a wheel that rotates once per day.
Then we could attach little actuators to that wheel that will hit the switch, and there you go -
you’ve just made a timer switch!
Let’s take a look at this consumer-grade timer switch.
This Intermatic Time-All was a staple of American life - or at least some American lives -
in the nineteen seventiesss? Probably?
I’m having a heckuva time tracking down specific dates for this model’s introduction
but it’s old enough that it doesn’t have a polarized plug - which makes it borderline useless today.
But, sure enough, it’s basically a weird-looking 24 hour clock that has a wheel instead of hands,
and hanging around the edges of that wheel are these little movable tabs marked “ON” and “OFF.”
You can move them by pushing them down, and then they’ll slide around the edge of the wheel.
Simply put the ON time where you want it, then the OFF time where you want it.
Of course, you also need the clock to be set to the right time.
You set the time by turning the wheel so that the current time lands where the “Time of Day” pointer is pointing.
Sticking out the side of the device near that spot is a little black knob that’s also marked “ON” and “OFF.”
That is the actual switch mechanism that the clock activates.
And when I turn the dial by hand, I encounter resistance once the tabs get near that knob.
Keep turning and you’ll see that the knob starts to move.
And right when the tab hits the “Time of Day” indicator
*click*
the knob snaps into the OFF position.
Cleverly, the ON tab can only turn the switch from OFF to ON -
if the switch is already on, well the ON tab doesn't do anything as it passes the switch.
Same goes for the OFF tab.
If the switch is already off, that tab won’t do anything.
This not only prevents the timer from slipping into the inverse of what you want,
but it also means that you can manually flip this to ON or OFF to give a temporary override without screwing up the programming.
The timer will resume normal timed operation when the correct tab hits the switch once more.
I’ll show you how that works in a moment
but I want to point out that since this really is just a clock attached to a switch,
that clock could be powered by anything.
It could be a wind-up mechanical clock,
or a battery-operated clock,
or even gravity driven with chains if you were particularly eccentric.
But as this thing's gonna get plugged into a wall outlet since...
that’s its whole thing, the clock mechanism is driven by a synchronous motor.
That's a special kind of motor that spins in lock-step with the frequency of incoming AC power.
Since grid operators do a fine job of making sure that power runs at exactly the right frequency,
and will even make adjustments day-by-day to account accidental for drift,
it serves as a reliable basis for keeping track of the time.
At least, usually.
Since the AC line voltage here runs at 60 Hz, that means the motor will spin at 3600 RPM (assuming it’s a single pole motor).
That’s, of course, way too fast so a ton of gear reduction is used to slow it down to
.00069 (nice) RPM or 1 RPD -
revolutions per day.
Anyway, here’s where the actual switching and the timing of that comes into play.
First let’s talk about the electrical switch that makes this thing useful.
In this timer it’s almost hilariously crude.
Incoming power from the blades runs right to the terminals of the outgoing receptacle, and -
woah.
Hang on, those terminals?
They’ve got bumps on them which actually engage with the holes in a plug!
Finally we found something!
No surprise it’s old.
Anyway, one blade has a simple wire link attaching it directly to the incoming power,
and the other runs through two formed pieces of brass that touch through a contact right here.
The pokey-outey knob of the power switch attaches to a shaft running through the timer body,
on the other end of which is a simple rectangular bit of plastic which either pushes the contacts apart or lets them the touch.
A simple 90-degree turn of that shaft is all that’s needed to change switch states.
As discussed previously on this channel,
electrical switches should have a snap-action to prevent arcing from damaging the contacts.
Here that’s accomplished with a simple arrangement of two pieces of metal which act like leaf springs.
They surround a square cross-section of the switch shaft,
keeping a slight amount of pressure on it and holding it in-place.
As the shaft is turned, the corners of the square start to distend the leaf springs by an increasing amount -
thus increasing the force required to turn the switch.
But once the square is just past the 45 degree mark into a turn, the springs will now help turn the switch
and it quickly snaps into the next position.
This design relies on the timer’s plastic shell to hold the top half of the spring in-place,
as well as to put pressure right on this spot of the brass link to make the contacts actually touch.
So then, here’s how the automatic switching happens.
There’s more going on with those sliding tabs than you can see from above.
As the dial turns with the passage of time,
the ON and OFF tabs slowly approach the switch knob.
The OFF tab has a protrusion that will collide with this wing on the switch shaft -
time marches on, though, so the tab will slowly rotate the switch.
And once it’s pushed it far enough, the switch snaps into the next position, opening the switch contact.
Notice that there are only two wings on the shaft - now that it’s in the OFF position,
the OFF tab on the timer’s wheel can no longer change the timer’s state.
The wings are parallel to the wheel and at this point are useless.
Further into the timer, though, we find another pair of wings on the switch shaft -
a pair in the opposite orientation as the first.
The timer’s ON tab has a protrusion just like the OFF tab,
but it’s positioned inward so it can only collide with this second wing.
Once it does, of course, it pushes the wing forward,
turning the shaft, and eventually it clicks over into the ON state.
This staggered arrangement is how the manual override can work without screwing up the timer settings -
the ON tab can only ever turn the timer on, and the OFF tab can only ever turn the timer off.
If it’s already in the same state as the tab would turn it to,
the tab has nothing to grab hold of.
This design also allows you to pull the switch knob out slightly,
which takes those tabs entirely out of alignment with the switch,
thus turning this into a manually-operated switch until you push the knob back in.
A nice feature, I suppose.
While this design works and works well,
it’s also somewhat limited.
You can only pick a single on and off time, and the shortest duration you can have between them is two and half hours.
To alleviate these limitations, eventually Intermatic would change this design from sliding tabs to removable tabs.
This timer here is one such example.
The overall method of operation is remarkably similar to the first timer.
We have a rotary switch, though now it’s up here,
and the on and off tabs simply push that switch into the next position when they collide with it.
The green tab turns it on, and the red tab turns it off.
The two tabs have their switch actuator pokey bits at different depths so, just as before,
the on tab can only turn it on and vice versa.
The similarities don’t stop there, though.
Internally we have a remarkably similar motor and gear reduction drive,
and the switch itself is still quite crude.
It’s also damaged on this one because
SOMEBODY decided they should hide a screw underneath the clock dial
and I didn’t figure that out until AFTER I went ham with a screwdriver and pliers.
Anyway, this time they’ve refined the switch
by making the switch blades double as the springs which provide that nice snap-action.
But otherwise it’s still just as crude -
are these wires even soldered to the motor leads?
Oh but this time they did at least take care to switch the hot leg.
In the old timer, if you installed it upright on the most-common outlet orientation you’ll find here,
the switch broke the neutral.
Very good.
I mean it wasn’t polarized anyway but still.
Anyway, since you actually remove and replace these tabs on this design to set the on and off times,
you can add more if you want a more complex program.
When new these timers came with two or maybe three pairs of tabs,
but tabs are very easy to lose and unfortunately Intermatic didn’t think of designing some sort of tab-holder into this to store them.
You’d think this might be for that purpose but nope, they don’t fit there,
so those extra tabs tended to disappear.
Don’t worry, they sell replacements!
Actually as a matter of fact you can still buy this timer new,
though stock appears to be dwindling.
Also, you can indeed put the tabs right next to each other and the timer will work -
so if you want something to be on for just a half-hour, well now you can do just that!
Luckily, at some point somebody asked
“why are we faffing with those tabs?” and designed a timer like this one.
Now, the face of the timer has 48 individuals tabs along its perimeter which can be up or down.
Annoyingly these things almost never bother with printing “up is off, down is on” so it’s always a game of trial and error setting one up,
but once you figure it out you’ve got all the flexibility this design could ever offer,
and without the risk of losing the tabs since they’re now permanently attached to the timer.
Internally, we still have a synchronous motor and gear reduction making the dial rotate once per day by way of this drive gear,
but now we have an off-the-shelf microswitch doing the switching with micro flair.
A simple lever connects the switch’s actuator to the perimeter of the dial.
In this design, the dial acts as a very slowly turning cam which that lever rides against.
When the tabs are in the down position,
they push on that lever which depresses the switch actuator allowing power to flow.
However, when they’re in the up position they leave space for the lever to fall into,
and that releases the switch, opening the contact.
Microswitches have their own internal spring mechanism to make the switch action happen quickly;
you can hear it clicking when I depress it manually.
*clicky clicky clicky click*
And since it always wants to push that actuator out,
the switch will in effect turn itself off as soon as the lever falls into the cam thanks to a pulled-up tab.
This design also allows for a simple slider to provide a program override -
slide this over and now the switch is pressed in regardless of the tab situation.
However, it won’t automatically resume the program like the Intermatic timers will.
It will only return to the program when you switch it back to timed operation.
Now, in case you haven't realized, it's 2023.
These days we have more phosticated ways of timing when things can and cannot get power.
But mechanical timers like these still have their applications.
I whip out a few during Christmas time for some indoor lighting displays.
And it can be nice to set up, say, a floor lamp on a timer like this to give you some light when you get back from a day out and about.
It may be basic, but it’s still automation.
And in the commercial realm, you still see similar timers used for things like defrost cycles in refrigeration equipment,
lighting signage so it goes out after closing time,
or even just exterior lighting in general.
Though photocells are usually a better option since the sun does that thing where the days get longer and shorter.
But as electronicals get cheaper and cheaper,
well now it’s just as likely that when you need a basic timer you’ll be getting something like this.
A microcontroller hooked up to a display, some buttons, and a relay
makes for a very flexible timer.
Want different programs for weekdays and weekends?
Knock yourself out.
Concerned about the time drifting with a power outage?
Well, just stick a little rechargeable cell on the board and use a clock crystal as your time base.
You can even get inexpensive timers which, after telling them where you are on the planet and the date,
will automatically adjust sunrise and sunset times throughout the year
all without needing WiFi or an app.
And that’s pretty neat.
Still though, I can’t help but admire the charm that is a clock which turns a switch.
Or, I guess, presses a button in some cases.
Take two basic things, smoosh them together,
and you can make a pretty handy new third thing!
Do it well enough, and you can even change the world.
Thanks to Mike for sending these timers my way way back when when,
and of course thanks for watching.
♫ regularly-scheduled smooth jazz ♫
I’ve been working on a pretty complex tompic…. Tompic?
Awwwghh
That’s it!
How ‘bout a taste of little November [laughs]
I mean, we all know how to make and break electrictcalkiconnec
I suppose this is a sufficiently obvious idea that it got incorp --
Dahh, I could’ve made that work.
I suppose this is a sufficiently obvious idea that…
it got implemented in one way or another…
just as soon as we figured out the light bulb.
Why is the pacing so wrong?
*click*
the knob snaps into the off position.
Except I just turned it on.
One blade has a simple wire link attaching it from the from the from the from thing.
Internally we…
good god!
So, it was just about time for this video, eh?
Do you think when doing inventory, after discovering a lack of certain herbs, a chef will yell
"we're running out of thyme!"?
I mean, if I worked as a chef, you can bet your bottom dollar that I would.
Every thyme.