Electronics can generally be divided into two types: Digital and Analog.

Whenever we’re measuring a voltage from a sensor or whenever a record player needle feels the scratches in a groove on a plastic record we’re dealing in the realm of analog.

Analog is useful because its what nature uses.  The sights, sounds and motion of the world around us are all working in analog.  In most modern technologies, however, we really are a digital age.  What distinguishes digital from analog for me is the fact that digital signals are represented as pulses or square waves that signal “on” and “off” as a “1” and  “0”.  This looks like a pulse to me and so I’ve told you that digital electronics begins with the pulse or heartbeat.

When we looked at some of the instruments we’ll be using to diagnose our circuits and programs in the robot we connected a signal generator to the oscilloscope and generated a series  of square, sine and V shaped waves at various frequencies.  We also saw how the signal generating probe would generate either a 400 pulse per second or a .5 pulse per second signal that we could trace in a circuit using the logic probe.  Later, we connected the oscilloscope to the output of the BOE-BOT board that gave instructions to the servo motor to move.  We saw that as we changed the pulse length in the program that the pulse-up and the pulse-down got further and further apart.

The true pulse, however is the one that is called the clock and is essential to any microprocessor, computer or digital process.  This is different than the “1”s and “0”s we spoke of.  This is the set of pulses that determine how fast the central processing unit (CPU) of a computer steps through its instructions and how often a microprocessor sends or receives signals.

boebot processorWhen I introduced you to the BOE-BOT I showed pointed out the chip that housed the microprocessor of the robot and called it the brains of the robot.

Unfortunately, its very small and hard to see.  What the company that makes the BOE-BOT has done is to take a very small microprocessor called a PIC (the largest chip on the board) and placed it on a little circuit board of its own called a BASIC STAMP.  On this board we can see a silver component with 20.o M written on it.  This is a crystal that oscillates at 20 megahertz (20 million cycles per second) but ours works at 50 megahertz.  This little computer can execute 75 million instructions per second at that rate!  You can’t tell from the picture but the crystal has two wires that are connected via the circuit board’s traces to the second- and third-pin-from-the-top on the right side of the PIC chip.  If your robot suddenly stopped working or was working sporadically, you might want to check the pulses at either of these two pins using the oscilloscope.

Want to know more

https://learn.sparkfun.com/tutorials/analog-vs-digital

http://www.parallax.com/sites/default/files/downloads/BS2-IC-Schematic-Rev-J_0.pdf

http://www.parallax.com/sites/default/files/downloads/27218-Web-BASICStampManual-v2.2.pdf

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