Digital Logic – Simple Computing System Example (2 of 2)
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Digital Logic – Simple Computing System Example (2 of 2)


In our last video, we
looked at what exactly a computer system was; and
we defined a digital computer system as being something
that had an input, and which produced an output based on some processing system in the middle. What we’ll do in this video
is take a look at very simple processing systems, or very
simple digital computer systems. For example, take a look at
a very simple porch light, or a garage light. Typically, garage lights or
porch lights, like these, are available in a lot of homes. Here’s a porch light
that turns on the light if it is dark outside, and stays
on until it’s morning time. What exactly… Let’s use this particular
porch light as an example to see if we can relate as
to exactly what the input to the system is, what the output is, and what the processing logic might be. What is the input to the system? The input is a sensor that measures the brightness outside. The output is the light; or
the light bulb being turned on. What is the processing logic here? The processing logic basically
is: this particular statement that we stated in plain English. We want to take the
plain English statement and decipher what the
processing logic would be if we were a computer. The processing logic
basically relates the input, which is sensor that measures
brightness in this case, to an output, which is the light. What is the processing logic in this case? Light, if we write it in
the form of an expression, the computer’s processing
logic would be that the light is equal to not bright. This basically means: the
output light is turned on if it is not bright outside. This is the input: if it
is not bright outside, this is the processing
logic that takes place, which results in the output
light bulb being turned on. So: input, output; in the
computer’s processing logic. Let’s make this a lot more complicated. Here’s an example of something else; I could find it on Ace Hardware. This particular kind of porch
light, or a garage light, basically turns on the light
not only if it is dark outside, but also only if it is dark outside and there is some sort of a motion. In plain English, I would
say: if it is dark outside and a motion sensor detects
someone at the door, turn on the lights. Let’s go through this particular example, and see if we can find
out what the input is, what the output is, and
what the processing logic of this computing system might be. The input is a sensor that
measures the brightness, and then the sensor that
measures or detects the motion. The output, again, is the
light bulb, and the computer’s processing logic says… Let’s take a look at this in plain English description, again. If it is dark outside, so the
sensor is saying it is not bright outside, and
there’s motion outside, then we should have the light on. Looking at the processing
logic: here’s the input from the motion sensor. If there’s motion outside
and it is not bright outside, meaning it’s dark outside,
then the left-hand side of this expression: the
light bulb should come on; that’s the computer’s processing logic. Let’s get a lot more complicated. What if I had this particular scenario: I love to work outside,
especially when it’s dark and I don’t want to have to
wave my hand at the motion sensor so that I can have light
outside when I’m doing work. So, maybe I’d tell you:
if it is dark outside and a motion sensor
detects someone at the door or I manually turn the switch
on, then keep the lights on. If it’s dark outside and
motion sensor detects someone at the door or if the light
switch is manually turned on, then turn on the lights. What are my inputs? In this case, my inputs
are a sensor that measures brightness just like before,
a sensor that detects motion just like before, and a manual switch. What is my output? The output is the light
bulbs, just like before. The processing logic for
this particular case is: Light sensor detects whether
it’s light or dark outside, so if it’s not bright
outside and the motion sensor detects there’s movement
or if my switch is manually turned on; my light bulb should come on if there’s motion and if it’s dark outside or if I turn on the switch manually. That’s my simple processing logic. You’re it’s feed different
versions of a computing systems of different degrees of complexity. Not bright; that was a very
simple computing system. A little more complicated systems; which was motion and not bright. Finally, the processing
system on the most complicated system we looked at, also
involved a manual switch; motion and not bright, or
if the switch is turned on. A computer system is basically something that acts on these inputs with some logic that’s embedded in it to
produce a desired output.

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