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DAVID MALAN: --start to implement
this notion of something

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either being one or a zero.

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Indeed, we could just do it over here.

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You know this next demo is actually
the result of a progression of demos.

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It was a few years ago where I had
always kind of talked in the abstract

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about turning light bulbs on as
representing one and zero, the presence

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or lack of electricity, and
then just on a whim I think,

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before one year's first lecture, drove
down the road to a Target, big store

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like Walmart, and grabbed
a few inexpensive desk

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lamps, the kinds of things
that you would like clip

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onto your shelf in college and--

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DOUG LLOYD: Those are flexible, yeah.

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DAVID MALAN: --and you've
got a few light bulbs.

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Yeah, these little goose-neck
things, and then I just

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attach them to the lectern on stage.

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And then it was actually
a great demonstration

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I thought, in retrospect, being able
to then literally turn the switches on

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and off, all our transistors on stage,
and have something very visible,

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let alone in a big space like this.

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DOUG LLOYD: Right, but the CS50 is
constantly reinventing itself every

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DAVID MALAN: I know,
creating work for myself.

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So these are-- yes, are binary bulbs.

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So you might recall, Ansel
Duff, a former advisee of mine,

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and an undergraduate here
majoring in engineering sciences,

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actually built these for us.

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And the vision was, he machine this
long tube that held eight light bulb

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sockets, and then we were really
on a kick with Hue light bulbs

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that semester, which are these
Internet of Things devices where

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you can actually control via an API
or application programming interface.

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And you'll see, we also went on Amazon
and got these little grade school

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refrigerator magnets for the one's
place, two's place, all the way up

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to the 128th's place.

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And so you'll see eventually
that I can take out

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an iPad where Ansel wrote some software
that talks via Wi-Fi to the light bulbs

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so that our student volunteers can turn
the lights on and off in a pattern.

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DOUG LLOYD: And the other cool thing
about having this magnetic tube

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or magnetic paint on
there is that a little bit

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later on when you see a second demo of
this, where we can sort of magically

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wipe the place values away--

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DAVID MALAN: Dramatically
wipe the place values away.

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DOUG LLOYD: And suddenly
we have the hacker edition

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version of the binary bulbs problem.

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DAVID MALAN: Indeed, which gets some
good like, oh, from the audience there.

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Though admittedly, I
think we actually over

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engineered the solution so to
speak, whereby this past year

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we actually reverted to not using
Hue's, but just using old school light

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bulbs and little toggle switches, which
were just so much easier to set up.

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These things are great when they work,
but honestly setting up the Wi-Fi,

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making sure we had our own private
network that all eight light bulbs were

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on, and the iPad was working,
it was just so many variables

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and it would be just awful if that
doesn't work in the first few minutes

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a class when you're trying to send a
message that, hey look how simple this

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is, but you can't even get it to work.

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DOUG LLOYD: What was great
about a demo like this,

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is you don't even need a rig as awesome
as the one that Ansel helped put

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together because a lot of
schools that might be--

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there's the dramatic wipe away--

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A lot of schools might want
to do something like this,

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but it's really easy to do
with just cell phones now,

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just turning on your
flashlight or your an app--

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DAVID MALAN: Indeed.

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DOUG LLOYD: --or an app like that.

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DAVID MALAN: And that's what I've
started doing when traveling and giving

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little demonstrations like this.

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It's just much easier than packing like
three big light bulbs in your suitcase,

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you just ask for volunteers.

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DOUG LLOYD: I can imagine getting
three of those lamps through the TSA

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would be very easy.

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DAVID MALAN: No.

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These days, no.

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So any form of lights work, or
barring that, a piece of chalk

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and a one and a 0.

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