In the modern world, when we want to make
something happen automatically,
we use these newfangled computer things.
Whether that means a huge industrial automation
system controlling robots in a factory, or
an Arduino you learned how to program to do…
whatever the kids do with Arduinos these days...
our modern world is based on bits of silicon
executing instructions.
It’s a pretty great place to be
- for now -
but to me it’s not all that interesting.
What is much more interesting to me is the
wild world of electromechanical wonders that is...
pretty much all general-purpose automation
from 1975-ish and before.
Electromechanics is my favorite kind of automation.
Why?
Because using nothing but switches, some motors,
some relays, maybe a solenoid or two,
and a heckuva lot of ingenuity, you can make surprisingly complex things happen,
all without a single bit of code.
For example, a jukebox!
This here is the Statesman, by Wurlitzer.
This beautifully brown beast hails from the
year 1970.
I mean of course it does.
This may be the ugliest jukebox ever produced.
It’s… even as an outspoken fan of the
color brown, this is not very attractive.
But!
At least with the lights on we get some purple!
Also known as the 3400 series, this jukebox introduced the new Wurlamatic record changer mechanism.
Which, sadly, was a radical departure from
Wurlitzer’s previous designs which put the
mechanism on full-display.
Here it’s hidden, but luckily I have the
key to open it up.
Now what this mechanism does is fairly obvious
upon a short glance.
I mean, it’s got a carousel of records,
an arm to grab hold of one of them and place it on
this little turntable, and so obviously the
carousel will rotate to a specific record,
stop, the arm will grab it, put it on the
turntable with the selected side facing up,
let go of it, then the tone arm will move
into position to play it, and once it’s
done the tone arm will return to its resting
position, the record-grabby arm will grab
it again, put it back, and we’re done.
So, let’s see how that works in action.
I’ll be selecting M3 which will play the
A side of the green record.
Pay attention to the sounds it makes.
[two clicks as buttons are pressed]
[a whirring mechanical sound]
[a clunk and a loud buzzing as the carousel moves]
[another clunk, whirring]
[two clicks]
[another click]
[whirring stops]
♫
Alright, and now that the record is over,
watch what happens.
[a click, followed by the whirring again]
[various mechanical sounds as the record is put back]
[carousel buzzes as it moves]
You might think that the carousel will stop
once it gets back to its starting position
[faint double-click]
but it actually continues for one more rotation.
Then, it comes to a halt.
[clunk, and buzzing stops]
Now you might ask, how does it know what record
to play?
What was the point of that sound before the
carousel started to move?
[button being pressed; whirring]
[buzzing of carousel]
And more generally, what are the brains of
this operation?
If there isn’t a microcontroller controlling
things all micro-like, how can it be controlled?
The answer is a whole bunch of weird, purpose-built
mechanisms,
rats nests of wires,
and a staggering number of switches.
That’s it.
Electromechanics are really quite simple as
a concept, but the applications can be a little complex
at least on the surface.
Before we get too far into the electro-side
of things,
let’s look at the mechanics more closely.
The heart of the Wurlamatic mechanism is right
here.
This controls everything the jukebox does
aside from record selection.
And all of its functions are performed by
a simple electric motor and a gear reduction drive.
Here, I’ve re-wired the motor to a constant
power source.
You’ll notice that it simply repeats the
same actions over and over again.
Grab the record.
Put it down.
Move the tone-arm.
Then the same thing in reverse.
It’s just a constant back and forth.
But notice how much it’s actually doing.
It may look like it’s just moving the arm
back and forth but it’s a lot more than that.
Most of everything that’s happening is happening
because of this one very complex mechanism.
The mechanism is powered by the main cam
motor underneath it,
and as the mechanism rotates, so do a series of cams.
A cam is a sort of oddly-shaped wheel that
rotates around a shaft, and thanks to its
odd shape, it translates rotational movement
into linear movement with the help of a cam
follower which gets pushed as the cam rubs
against it.
In fact built into the drive gear is a vaguely-heart-shaped
groove which serves as the cam that operates
the record arm.
It’s a little hard to see, but there’s
a little peg riding in this groove, and it
causes the record arm to pivot backwards,
away from the record carousel with the help
of this little ratchet and gear thing.
At its pivot point, these three gears serve as the means by which each side of the record is selected.
Pins on the two side gears will stop either
one of them from turning when they hit these catches.
This then causes the arm to rotate sideways
as it continues to pivot backwards.
Depending on which pin is stopped, it will
rotate in either one direction or the other,
and this solenoid moves the catch points back
and forth, therefore its position determines
which side is played.
In its resting state, it will rotate to play
side B by default, and when the solenoid
is energized, it catches the other pin to
play side A.
Obviously the most noticeable thing this mechanism
does is move the record take-out arm,
which is its official name, by the way.
But thanks to a series of other cams adjacent
to the main drive gear, and the various linkages
they attach to, it does much more, too.
The single cam in front of the main drive
gear releases the record from the arm by way
of this linkage, which also pulls the turntable
slightly to the left so the record can spin
freely of the arm.
Two of the cams behind the drive gear move
the tone arm to play the record, with one
responsible for lifting it up and the other
for moving it left and right, and there’s
even a cam just for activating this little
button which switches the amplifier from its
auxiliary input to the phonograph input when
a record is being played.
Take a look at this exploded diagram.
This is everything going on inside the Wurlamatic
mechanism.
There are 7 cams in total, though that’s
not perfectly true as you’ll see later.
But anyway, these seven cams are the programming
of the physical actions that take place.
Their shape and position dictate at what points
in the mechanism’s 360 degree rotation
each action will occur.
This may not look like a program, but it very
much is.
Note that the cams could be made to cause one
action to happen multiple times per cycle,
if required.
However, this clever mechanical program doesn't
make for a useful jukebox all by itself.
If it just runs all the time, well then that
wouldn’t do anything but make a bizarre
record flinging dance.
We need a way to control when the program
starts.
Of course we also need to pause the program
in the middle when the arm has reached the
turntable so the record can actually play.
And then we'll need to restart the program to
put the record back.
Of course, finally there needs to be a way to shut down
that program altogether once that task is complete.
So we need some sort of additional control.
Of course, before I re-wired the motor, it
didn’t start moving until the correct record was in place,
and it was automatically stopping
in both the record playback and its resting positions.
How did it do that?
Well, what makes it automatic is the plethora
of micro-switches you see all over the place
that function as interlocks, interrupts, start-stop
points, and triggers for other ancillary actions.
OK, so here’s something that’s super common in electromechanics
and is gonna come up a few times here.
Self-latching circuits with interrupts.
Using a relay, we can design a circuit that
will latch itself in a closed state
until another action occurs.
What is a relay?
Well, a relay is an electrically operated
switch.
A small electromagnet within the relay opens
or closes any number of switch contacts.
One of the most common things we do with relays
is control high power devices with low voltage,
low current control circuitry.
But we can also be almost endlessly clever
with them.
So, let’s say we want to turn on this light
bulb with a momentary pushbutton switch.
We could wire the bulb right to the pushbutton,
but of course that means it’s only lit
so long as the button is held in.
And it also means the button has to handle
all of that current.
What I want is for the button to turn the
light bulb on, and for it to stay on
after the button is released.
Here’s a simple circuit which will accomplish
that by latching itself closed.
12 volts DC power is used here on the control
side of the relay,
but the load side of the relay can be whatever we want it to be.
This relay is now the switch which turns the
light bulb on, and it will do so whenever
the relay receives 12 volts DC power.
So, we’ve got a 12 volt supply and a ground for the relay, with the bulb wired on a completely separate
120V circuit through one of the normally
open contacts of the relay.
If I wire the 12 volt supply through the pushbuton,
now the relay will energize whenever the button
is depressed, which closes the switch contacts
inside the relay, and turns on the light.
This also has the benefit of making the button’s
electrical connections safe to touch, since
they’re now just handling 12 volts.
But, the light still goes out as soon as you
release the button because the relay loses
its 12v power source.
However, if I branch off the 12 volt supply to another of the normally open switch contacts of the relay,
then feed the other side of
that back into the control side input,
what now happens is that as soon as I push the
button, the 12 volt control side becomes self-powered.
The button is now completely out of the picture,
as it becomes bypassed by the relay itself.
The relay is now stuck in the closed position,
or latched… forever.
At least, until the power supply is cut.
Taking a closer look, we now have a second
power source coming from before the switch.
This has 12 volts on it at all times.
Again, it’s going to the second set of switch
contacts of the relay, and its output is being
fed back to the control side.
If there’s no power from the button, well nothing
happens.
But as soon as the button supplies power,
that second wire snaps into action,
bypassing the button, and keeping the relay energized.
But, if I cut that second wire feeding the
relay and put a second button across it,
this one with normally closed contacts, that means I
can interrupt the 12v supply that’s keeping
the relay energized in order to deactivate it.
Now, I press the “on” button, which energizes
the relay.
This of course turns on the light bulb, but
also creates that new 12-volt supply for the relay
to stay on indefinitely, but that new supply
now travels through this second button.
When I press it, it momentarily breaks the
12-volt supply to the relay, which de-energizes it,
and the light goes out.
However, as soon as the green button supplies
12 volts again, even for just a tiny fraction of a second,
the relay provides a bypass
for itself once more, and the light stays on.
Pretty clever, huh?
There are all sorts of applications for a
circuit like this.
For example, a garage door opener!
Push one button, the motor starts, and it
doesn’t stop until a limit switch at the
end of the door’s travel opens the circuit.
Of course, you’ll also want to design in
some safety interlocks, and other stuff, but hey.
It would work.
It might also kill someone.
But it would work!
So then, how does this apply to the jukebox?
Well, the Wurlamatic has a microswitch that
serves as an interrupt to a latched relay.
It’s the red button in our previous example.
It rides along the edge of the main gear.
That’s why I said there are more than seven
cams, because this is also its own kind of cam.
Once the program is started, it will continue
to run on its own because a relay, specifically
the Main Cam Relay, is latched in.
But it’s latched through this, the transfer
switch.
Now, you’ll notice that the switch doesn’t
actually get actuated...
♫ abruptly slow jazzy blues kinda music ♫
Ooh, twangy!
Now, you’ll notice that the switch doesn’t
actually get actuated until the main cam has
moved a little bit.
Why is that?
Well, because at first, either the Side 1
or Side 2 relay serves as the power source
for the main cam relay.
Electromechanics can get a little complicated.
The same device can receive power from multiple
places, but so long as you sequence things
correctly, you can manage it.
When the carousel has reached the correct
selection, either the side one or side two
relay will be activated.
That starts the main cam program, just like
pushing the green button.
However, the signal from the first relay will
disappear shortly after the record arm has
moved from its resting position.
We’ll get into the specifics of why that
happens when we get to the delightfully named
Selection Accumulator.
To put it more simply, a signal caused this
motor to start turning, just like the green
button turned on the relay.
But to keep it turning we need to generate
a new signal because we’re gonna lose the
first one, just like releasing the green button.
And that’s what this switch does.
The transfer switch keeps the main cam relay
energized, and thus the main cam motor running,
all the way through its rotation, until the
record is put back at which point it is released.
But wait.
That’s…
a problem.
Doesn’t it need to stop midway through to
actually play the record?
Indeed, it does!
So, there is another switch at play here,
appropriately called the Play Switch.
This is actually a sort-of second red button
in this scenario,
but it’s not going to totally kill the circuit.
Instead, it will just sort of pause it.
Ironic for a switch named Play.
Whenever the transfer switch is engaged, the
main cam relay is, too.
So it wants to move the mechanism.
But, once the play switch is activated by
this cam, it interrupts the flow of power
from the transfer switch and de-energizes
the main cam relay.
This then causes the entire Wurlamatic mechanism
to stop.
And now the record can play.
Incidentally, this switch does double-duty
and the same switch which mutes the
amplifier’s auxiliary input to give priority
to whatever record is playing.
The key difference here is that the transfer
switch is still trying to sending power to
the main cam relay, but it’s being interrupted
by the play switch.
So what happens when the record is over?
If this circuit was designed like our red
and green button thingy,
well if the red button's being held in,
we would need another green button to provide power and start it back up.
Do we have one?
Well, yes!
That’s the trip switch, located right here.
It’s activated by the tone arm once it’s
near to the run-out groove of the record.
This then bypasses the play switch, allowing
current to go around it, and thus re-energize
the Main Cam relay to restart the program.
Now here’s a bit of nuance which is very neat and I want to highlight it.
The trip switch works as a bypass for the
play switch, right?
Which, again, the play switch stops everything
so the *record* can play.
The play switch isn’t letting power through
to the main cam relay, but the trip switch
provides a workaround.
But that means that the programming of all
these cams needs to be done such that the
play switch gets released before the tone
arm is pulled back to its resting position.
Otherwise, the play switch would just cause
things to come to a halt once more as soon
as the tone arm moved away from the trip switch.
You can see that things were programmed just perfectly
so that the play switch gets released, then the tone arm moves
This is why electromechanics are so fascinating
to me.
It’s a delicate ballet of logical circuit
design and physical interactions.
You need to make this action to stop?
Well, just make it hit a switch that kills
it.
Oh, you need it to start up again?
Well, just add another switch that un-does
the first one.
And make sure you get the timing right or
it won’t work at all!
Basically, there are a ton of if/then statements
in here, but manifested as wires and switches.
It’s a form of logic, but very rudimentary.
When you combine that with crazy mechanisms
like the Wurlamatic, you find yourself with
a machine that can do surprisingly complex
things all through whatsists and doodads.
None of that there computery business.
And you'll also find some important safety interlocks,
too.
For example, notice how when the record grabby
thing grabs the record from the carousel,
it ends up between the two records surrounding the one it’s grabbing.
Well, what if the record carousel were to
move with it in that position?
A bunch of records would be broken by the
little hook.
To keep that from happening, the motor which
turns the carousel is wired through this microswitch,
which is only depressed when the Wurlamatic
mechanism has opened the jaw of the…
right, the take out arm.
That’s what it’s called.
This prevents what we in the business call
"a bad day".
And of course you’ll find some other switches
here that do other groovy things, like the
Side 2 Release Switch.
This is what actually releases the side 2
relay.
There’s another one, of course, for the
side 1 relay, and these function just like
the red buttons in our little demo rig.
Both the side 1 and 2 relays are self-latching
to get the main cam relay, and thus the entire
mechanism going, and these two switches are
responsible for releasing them.
You’ll notice that it’s the same pins
which are used to turn the take-out arm that
actually actuate these two switches.
But of course, we haven’t answered perhaps
the most important question about this machine.
What gets this all started?
How does it know to start turning the carousel,
and how does the carousel know what record to stop at?
Or what side to play?
Well, I’m gonna save that for the next video.
Yeah I know, I know, I’m sorry, but this
is already, what,
[NINETEEN]
minutes long?
Or thereabouts?
But before I go, let’s look at one more
thing.
I bet you didn’t think you could just remove
the record carousel, but you can.
It’s actually just sitting in here.
Just select a record to be played, then shut
if off.
[sound of music stopping[
Now, the carousel can simply be lifted up
and out.
Look at what’s underneath.
It’s connected to this black arm which can
be spun around.
This is clearly going to some sort of mechanism
below it.
That mechanism is the Read-out Arm and it,
along with the Selection Accumulator,
are perhaps the most amazing parts of this entire
machine.
The Selection Accumulator is what made the sound you
heard before everything got started.
This one.
[rapid clicking, followed by whirring]
[click]
[carousel spinny-buzz begins]
Notice when I select a record that the buttons
stay depressed until that sound stops.
Then they pop back out.
That's actually the reason there's a reset button in the middle,
so that way if you press the wrong button you can pop it out.
Now, listen closely as I select a series
of records.
A1
[whirring]
[clunk as it stops]
C1
[whirring]
[click]
[whirring]
[clunk as it stops]
E1
[whirring]
[click]
[whirring]
[clunk as it stops]
G1
[whirring]
[click]
[whirring]
[clunk as it stops]
and J1.
[whirring]
[click]
[clunk as it stops]
Did you notice something changing with each selection?
[whirr...
[whirr...
click]
[whirr...
click]
[whirr...
click]
[whirr...
click]
What's going on?
Well, stay tuned because in the next video
we’ll find out.
Thanks for watching.
I really hope you enjoyed this video and that
my explanations were easy enough to follow.
Electromechanics are really quite simple,
but they can be a little confusing.
When you use switches and relays to make sequences
and interlocks,
it can seem to get out of hand.
In fact, these here are the schematics for
this machine.
They’re super easy to read!
You might have thought this was a pretty simple
device with what you’ve seen up ‘till now,
but trust me.
When we explain where these buttons go, it’s
gonna get a lot more complicated.
I think I’ll play some music now.
How about…
T1?
[ buttons being pressed ]
[ selection accumulator whirring ]
[ buzzing as carousel moves ]
this is gonna take a while...
shoulda picked something in the C's or D's...
[ clunk, followed by various mechanical sounds ]
[a low hum]
♫ scratchy low-fidelity smooth jazz ♫
♫ audibly improved smooth jazz ♫
I liked that delivery so much and then it
fell apart!
And a staggering number of switches, rel … ooh.
Ha, that’s the, that’s the end of the
sentence!
[laughs]
oops.
Did I say “of course” weirdly?
It’s a little late now, ‘cause I’m already
moving it back, but I think I did.
However, this clever mechanical program wouldn’t
make for a useful jukebox…
it’s later than you think it is, I’m kinda tired.
When I press it, it morment...
[weird stress
sounds]
Those are fun words!
They aren’t words, they’re just sounds
So what happens when the record is over?
Oh.
It’s not phrased as a question that I know
the answer to.
I should have added a paragraph here.
I need to…
I need to say something that’s not in the
script.
That’ll go well.
Stay tuned for next time when we 
ACCUMULATE SOME SELECTIONS
I'm very excited for the next video.
I think you're gonna like it.
doo doo doo doo
