Download UMass Amherst FFYS 197 ECE Fall 2014 Course Note1. Prof

UMass Amherst
FFYS 197 ECE
Fall 2014
Course Note1. Prof. M cLaughlin
Class meeting #1 took place Monday 9/8/14. We spent ~ 30 minutes in introductions, discussing
the basic concept for the course, and touring the craft center. Participants were asked to spend
some time thinking about the kinds of projects they might like to spend the semester working on
(eg, working alone or in a 2 or 3 person team or a larger group; making a sound-activated, lightup tie; making a piece of art; a lightscape for a room; etc…)
Class meeting #2 will take place Monday 9/15/14.
Our first topic will be a brief brainstorming session about projects. We’ll come up with a list of
ideas, including some that are very straightforward/practical/doable, some that are wildly
creative/probably not doable, and some in-between.
Next, we will arrange ourselves into 2-person teams and do some basic electronics work using
a lab kit that will be provided to you. The components in your kit are as follows:
Wire Stripper (1)
Multimeter (1)
4xAA Battery holder (2)
Resistors:
Asssorted (10 of each)
LEDs:
Red (2) Yellow (2)
Green (2)
Capacitors:
0.1 µF (2)
10 µF (2)
Gemma w/ USB cable
(1)
CdS cell (1)
Medium Breadboard (1)
Large Breadboard (1)
Arduino w/USB cable
(1)
DC Connector (1)
Wire (4ft/ color) (3)
AA Batteries (8)
1 Electricity basics:
Circuit: a closed loop comprised of batteries, resistors, light emitting diodes (LED’s), and other
devices, interconnected by conducting wire.
Voltage: a measure of the energy difference between the two terminals (the two wires) of a
circuit element having units of Volts or Joules/coulomb. The AA batteries supplied in your kit
each produce 1.5 V between the terminals. Two of these batteries hooked up in series (end-toend) will produce 3 V. Charges that enter the – terminal and exit the + terminal will have gained
3 Joules per coulomb as a result of the chemical forces in the battery. When hooked up in a
circuit, these voltages will drive charges around in a loop. The LED’s in your kit have a 2 V drop
across their terminals. Charges entering the + terminal (anode, or longer lead) and exiting the –
terminal (cathode, or shorter lead) will have lost 2 Joules/coulomb of energy. (Where will the
energy have gone?) You can measure voltage using the digital multimeter (DMM) in your kit.
Current: the flow rate of charges around a circuit having units of Amps or coulomb/second
The circuits we deal with will involve currents measured in fractions of Amps. LED’s typically
produce a satisfactory glow with 20 mA (0.02 A) of current.
Power: the product of voltage times current, having units of Watts or Joules/second.
Energy: the product of power times time, having units of Joules. Each of the AA batteries
supplied in your kit has a stored energy (when fresh) of ~ 5000 Joules or 5 kJ.
Kirchoff’s Voltage Law (KVL): the sum of the voltage around any closed circuit = 0.
Ohm ’s Law: the voltage across a resistor is equal to the resistance times the current flowing
through it. V=IR.
Resistor Color Code: Resistance is measured in Ohms. You can determine the resistance of
any resistor by noting the colored bands and using the table below. Or you can measure the
resistance using your DMM.
2 With these definitions and concepts, you can now build and analyze simple circuits and begin
designing light circuits.
1. Build this circuit and measure the voltage across each device as well as the current flowing
through the loop. Try changing the value of the resistor and note what happens to the
brightness of the LED. Can you determine how long the LED would glow if you kept the circuit
running until the batteries were depleted? How many hours would you get if you ran the LED
very bright? Medium intensity? Low intensity?
3 2. Try this circuit, which shows you how to hook up multiple LED’s. How long would the
batteries last in this case if you left this circuit running?
3. This circuit shows what happens when you try to run current “the wrong way” through an
LED. It won’t glow. Try reversing the red and black wires used to bring battery power to the
breadboard. Make sense?
4. Now take the Arduino UNO microcontroller out of its package and inspect it. The next set of
experiments will involve using this device to blink some LEDS under software control.
Download “Arduino in a Nutshell,” version 1.8 from this URL: http://hci.rwth-aachen.de/arduino
This is a free e-book by Prof. Jan Borchers, from Aachen University (Germany). Read the first 8
pages and see of you can hook up an LED to the Arduino Board and make it blink under
software control. As discussed in Prof. Borchers’ book, you’ll need to download the opensource Arduino Integrated Development Environment (IDE) from this site,
http://arduino.cc/en/main/software
We will spent some time in next week’s class getting all the teams up to speed with this blinking
light experiment. Then we’ll begin to plan our projects.
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