DESIGNING PHYSICAL INTERFACES:
interacting with our world
New Mexico Highlands University
May 31 - June 9, 2004
instructors: eric forman & cynthia lawson
LECTURE 1: ELECTRONICS PRIMER
ELECTRICITY
CIRCUITS
- Closed circuits: the types of circuits needed in electronics applications.
- Open and short circuits are important to define and understand since
they are the first steps in troubleshooting a design.
- Series and parallel circuits:
- In a series circuit, elements have the same current flowing through
them. In a parallel circuit, components have the same voltage across
them, with the current branching off to one component and the other.
- The total resistance of two or more resistors in series is equal
to the sum of the individual resistances. For n number of resistors
in parallel, 1/Total R = 1/R1 + 1/R2 + ... + 1/Rn
TOOLS
- Multimeter: Measures Voltage, Current, Resistance, Continuity
- Most multimeters can be used to measure voltage, current, resistance
and continuity, among other electrical properties. To measure voltage,
the red probe should be placed at the point where voltage needs
to be measured, and the black probe should be placed at ground.
The number on the screen will then need to be multiplied by the
factor being used in the measurement (usually on the voltage dial
on the multimeter). A negative number indicates either a negative
voltage drop or that the tips are inversed.
- To measure the resistance of a resistor, with the dial on Ohms,
each probe should go to one of the ends of the resistor. Again,
the number on the screen has to be factored by the multiplier indicated
on the dial. It is important to remember that to measure current,
the tips of the multimeter must replace that segment of the circuit,
so as to not cause a short.
- The test for continuity is essential in troubleshooting a circuit,
and checking that connections are where they should be. Continuity
between two points, indicates that current will flow freely between
one of those points and the other. To test this, the dial on the
multimeter should point to an icon indicated a speaker, or sound.
Then, each probe should touch one of the ends of the continuous
(multimeter will beep), or not (nothing will happen), connection.
For example, to make sure a circuit is not shorted, with the multimeter
on the sound icon, place one probe on power and the other on ground.
If a sound is produced, power and ground are connected, i.e. the
circuit is shorted.
- Soldering Iron: Creates a solid union between elements for electrical
continuity (Wire to wire, chip pin to wire, wire to resistor, etc.)
- Prototyping Boards (Breadboards)
- When designing a circuit, a prototyping board (or breadboard)
is used to test connections, and even an entire circuit, before
soldering or making a printed circuit board. It is important to
understand how a breadboard is wired, so as to ensure continuity
between desired elements. Although there are different types and
sizes of breadboards, it is safe to assume that continuity extends
along the side perforations (horizontal in this picture), and in
rows in the middle section (vertical in this picture). To be sure,
however, it is a good idea to test the continuity of the board (with
a multimeter) before starting to put the circuit into place.
- Note that the central gap in the middle section cuts continuity
between rows. You’ll see later how this is useful to keep the
sides of IC chips isolated.
- Blue and red lines are commonly printed on the board as a convenient
reference to power and ground. Some boards only have one power or
ground line, or “bus,” on each side - the kind pictured
here, with power and ground buses on each side, are easier to use
but are a bit more expensive.
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