1. Agenda Introduction to circuits Building a simple circuit
Introduction to Engineering Lab 3 -1 Basic Electronics with Circuit Prototyping
Agenda
Introduction to circuits
Building a simple circuit
Originator: Mike Hoffmann 02/22/01
Assumes a lecture on basic electronic circuits was given in ‘basics’ class.
Presenter must be prepared to ‘talk’ the students through the construction and use of a simple electronic circuit. Time limits and program objectives limit the amount of info covered. The intent is to convey only very basic info and concepts, and to spend most time with hands-on activity. Schematic symbols appear with each electrical component where appropriate.
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2. OVERVIEW MAJOR TYPES of ELECTRONIC CIRCUITS COMPONENTS and SYMBOLS
PROTOTYPING BOARDS
POWER SUPPLIES
DIGITAL MULTIMETER
DIGITAL COUNTER
SCHEMATIC CIRCUIT DRAWINGS
SIMPLE CIRCUIT, BUILD AND USE
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3. ELECTRONIC CIRCUITS DIGITAL ANALOG
OPERATION EXHIBITS A FINITE NUMBER OF DISCRETE CONDITIONS (e.g., ON/OFF) AND IS RELATIVELY INSENSITIVE TO NOISE
ANALOG
OPERATION EXHIBITS AN INFINITE NUMBER OF DIFFERENT CONDITIONS AND IS RELATIVELY SENSITIVE TO NOISE
Digital or Analog. In ENG 181, analog and digital measurement systems were discussed. Remember that circuit operational characteristics determine whether a circuit is considered ‘digital’ or ‘analog’. Most digital circuits exhibit operation of active components in their ‘saturation’ region and usually have only two states; active components in analog circuits must avoid saturation and remain in a ‘proportional’ region with an infinite number of states. ‘Saturation’ is a state where an increase in input signal results in no additional increase in output signal (also when a decrease in signal results in no decrease in output signal). Operation in saturation offers higher noise immunity (a good thing). FM radio station audio signals are less noisy than AM signals because, by design, the FM circuit elements are in saturation (in amplitude) much of the time. Note the square wave and the sine wave. The square wave represents a system operating in saturation mode. The sine wave illustrates the continuous nature of an analog signal.
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4. ELECTRONIC COMPONENTS
SWITCHES
RESISTORS
CAPACITORS
LIGHT EMITTING DIODES
CADMIUM SULFIDE PHOTOCELLS
TRIM POTENTIOMETERS
TRANSISTORS
INTEGRATED CIRCUITS (ICs)
Most components used in 182 are presented
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5. SWITCHES NUMBER OF POLES (contact pairs)
TYPE OF ACTION (bi-stable, momentary, etc.)
BODY/ACTUATOR STYLE (micro, toggle, button, chassis mount, etc.)
MICROSWITCH, LEVER ACTUATED, SPDT C
ENG 182 labs have single pole, double throw, momentary switches (SPDT) that are used as single pole single throw switches. The switch body is a microswitch with a lever for actuation. Push on the lever and the switch changes state. Release the lever and the switch returns to its original state. The schematic symbol is to the right of the photo. This switch has two positions (states). Its ‘rest’ state (lever not pushed) determines the pole definitions. ‘C’ is the common terminal, ‘NO’ is the normally open terminal, and ‘NC’ is the normally closed terminal. In this lab we use the ‘C’ and the ‘NO’ terminals. The ‘resting’ normal position is illustrated. When the lever is pushed, the switch connects the ‘C’ terminal to the ‘NO’ terminal. A momentary switch is ‘active’ only while the actuator lever is held. Bi-stable and multi-position switches remain in the position they are put in. Other info about switches such as make-before-break or make-then-break, etc., is beyond the scope of this course. NO NC
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6. RESISTORS RESIST THE FLOW OF ELECTRICAL CURRENT NO POLARITY
POWER LIMITED
UNIT OF MEASURE IS OHMS
COLOR BANDS INDICATE VALUE, TOLERANCE
A 100 Kohm Resistor
Resistors are used to limit current flow in either direction (no polarity). The result is a drop in voltage across the resistor and the generation of heat. Resistors come in many standard values of resistance and tolerance, many power ratings, various materials, and many package styles. Too much power loss (i.e., heat generation) by a resistor will cause it to fail. Consequently, a resistor of at least the correct resistance and power rating must be used in a circuit design. We typically use 1/4 watt resistors. They are sometimes metal film 2% tolerance. Other types are carbon or wire wound.
Color band codes (are used left to right as viewed above for ten, units, scaling, tolerance):
Brown/Black/Yellow Red Means: x 10**4 = 100, % tolerance
Black-- 0
Brown—1
Red-----2
Orange-3
Yellow—4
Green---5
Blue-----6
Violet---7
Gray----8
White--9
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7. CAPACITORS
HOLD AN ELECTRICAL CHARGE THAT VARIES WITH CURRENT (VOLTAGE)
VOLTAGE LIMITED
UNIT OF MEASURE IS FARADS (but generally expressed in micro, nano, or pico farads)
Polarized and Non-polarized Capacitors
Capacitors ‘resist’ a change in voltage. If voltage across a capacitor is not changing, then there is no current flow through the capacitor. They give up charge (current now flows) when applied voltage drops, and take on charge when applied voltage increases. They can handle only up to a rated voltage, and can be damaged if the rating is exceeded. They may be polarized or non-polarized. Polarized capacitors must be properly oriented in a circuit. The circuit will not work as expected and the capacitor may be damaged if oriented incorrectly. They have a marked lead and that lead, sometimes marked +, but sometimes marked - , must go to the respective higher or lower voltage points in the circuit. Non-polarized capacitors may be oriented either way. Capacitors come in various values and tolerances, body styles, and materials. +
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8. LIGHT EMITTING DIODES PASS ELECTRICAL CURRENT IN ONE DIRECTION ONLY
EMIT LIGHT PROPORTIONAL TO CURRENT THROUGH DIODE (over limited range)
MUST HAVE CURRENT LIMITED BY A RESISTOR IN SERIES
Diodes are semiconductor devices that allow current to flow in one direction only. They will completely stop the current flow when reverse biased (as when it is inserted in the wrong orientation). A diode as oriented in the schematic illustration would conduct conventional current flow ‘left to right’. Certain diodes emit light when a current flows through them. They are called light emitting diodes, or LED for short. A resistor to limit the forward current flow (to less than 20 milliamps for the LED we use) must be used. Further, the one pictured above is a focused LED meaning the emitted light is focused to a somewhat narrow beam. Others emit diffused light. +
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9. CdS PHOTOCELLS RESISTANCE THAT VARIES WITH INCIDENT LIGHT
SENSITIVE TO ALL LIGHT (whether from LED or room lighting)
POWER LIMITED
Cadmium Sulfide Photocell is a resistive component that is sensitive to incident light. Generally, the more intense or direct the light, the lower the resistance of the photocell. The ‘dark’ resistance of the photocell may be tens of 1000s of ohms, sometimes higher; while ‘light’ resistance may be less than 1000 ohms. The ones we use are about 2000 ohms with normal flourescent room lighting. Because they are essentially resistors, photocells have limitations concerning power dissipation. They can stand only so much heat before they fail. In fact, photocells should be used at the lowest average current possible, especially if used with hot light sources.
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10. TRIM POTENTIOMETERS RESISTANCE THAT VARIES BY MANUAL ADJUSTMENT
SLOTTED KNOB USED TO MOVE INTERNAL ‘WIPER’ ACROSS RESISTANCE
POWER LIMITED
A trim potentiometer is a resistive element which has a slider that traverses a resistive material. The resistive material can be carbon, ‘cermet’ ( a ceramic type material), wound wire, or any of a number of synthetic substances. The mechanical parts of the potentiometer are a leadscrew, slider, and knob. Turning the knob causes the slider to traverse the resistive material, thereby varying the effective resistance as measured across terminals 1 and 2 or terminals 2 and 3. The resistance across 1 and 3 is constant, regardless of slider position, and is the resistance value of the potentiometer. Because it is a resistance element, its unit of measure is ohms, and it is power limited. 1 2 3
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11. TRANSISTORS CONTROL THE FLOW OF CURRENT IN ONE DIRECTION
MUST HAVE CURRENT LIMITED BY LOAD AND/OR ADDITIONAL RESISTANCE
A transistor is a semiconductor device that controls the flow of current in one direction. With a relatively small control current, a larger current can be controlled. That is current amplification. A transistor is like a diode with a ‘control valve’. The ‘control valve’ (base terminal) is used to change the current flow through the transistor. The transistor we use in lab is a bipolar, NPN, small signal transistor. We use it as a switch, either on or off. It will survive many more operations than an electromechanical switch (relay). Conventional current in an NPN flows from collector (C) to emitter (E). The base (B) is the controlling terminal.
Another type of bipolar transistor is the PNP where current flows from emitter to collector. There are various other types of transistors besides bipolar. Field effect (FET) would be an example. E B C
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12. INTEGRATED CIRCUITS
MANY TRANSISTORS, RESISTORS, AND CAPACITORS ON A SINGLE SILICON WAFER TO PERFORM SPECIFIC FUNCTIONS
THE WAFER IS MOUNTED TO A CARRIER FOR EASE OF USE AND HEAT DISSIPATION 1 5 8 4 7
Some ICs are analog because they deal with continuously changing input. Some are digital because they are designed to deal only with binary (two state) inputs. They have various pin counts but 8, 14, 16, 18, 20, 24, 28, 40 are typical for dual-in-line-packages (DIP). The pins are numbered consecutively and counterclockwise around the IC. The pin 1 end or pin 1 itself is marked with a notch. However, there are many package designs for today’s many different ICs. Some are encased in plastic, some ceramic (heat transfer reasons). Surface mount are popular because they save board space, can be easily mounted by machines, and have good heat transfer character. We use standard plastic DIP packaged ICs in the labs. That type is illustrated above.
Notches mark pin 1 end or pin 1 of IC
(highlighted for clarity)
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13. PROTOTYPING BOARDS Bare Prototyping Board
The prototyping board allows you to easily build analog and/or digital circuits without the need for a printed circuit board. It has many sets of holes. Each set of holes is electrically ‘common’ (connected) within its group. This makes it easy to build a circuit. It also allows for re-use of the components. Also, the board has power and ground ‘busses’. These are special groupings of holes throughout the board which can bring current to various places (power bus) and return current to the supply (ground bus).
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14. PROTOTYPING BOARDS Bare Board Power and ground terminal posts
This prototyping board requires an external power supply. Seen here are four terminals, allowing for a ground connection and three different voltages. You must still connect from these to the power and ground buses on the board.
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15. PROTOTYPING BOARDS Bare Board Power and ground terminal posts
5-hole sets, electrically common (connected) internally
The board has simple electrical connections internally. There are two sets of rows of five holes, separated by a groove. Each row of five holes is electrically connected, and is not connected to the row of five holes on the other side of the groove. The groove allows parts such as ICs to have separated sets of connections for each pin.
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16. PROTOTYPING BOARDS Bare Board Power and ground terminal posts
Power bus (red/solid)
Ground bus (blue/dashed)
The ground bus is conventionally marked with blue. The power bus is marked in red. It has gaps between sections that must be jumpered if the same power source is to be distributed thru all sections.
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17. PROTOTYPING BOARDS Bare Board Power and ground terminal posts
Jumpers for complete distribution of power
To supply power to the entire board, jumpers are installed at the gaps in the power and ground buses. You should choose the jumper length so that it is the same as the gap between the holes. That method allows all the jumpers to lie flat, and not be easily snagged.
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18. PROTOTYPING BOARDS Bare Board Power and ground terminal posts
Connecting to the work space
To connect power to the work space, just connect a jumper from the power bus to a hole in a row of five. Then connect a jumper from ground bus to a different row of five.
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19. POWER SUPPLIES BATTERIES AC to DC POWER SUPPLIES
Most people are familiar with batteries. Batteries can be used in portable equipment or in cases where an electrical source is needed on a temporary basis. And in situations where the voltage source does not have to be regulated (battery voltage decreases with power draw).
AC to DC power supplies are used in many, many applications. They convert ‘house’ power (120 VAC) to a direct current and voltage. They can be voltage or current regulated, or can be unregulated. In lab we will use a regulated power supply to provide the stable 5 volt direct current source needed by the circuits. Two styles of power supplies, as pictured above, are used in the labs.
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20. DIGITAL MULTIMETER MEASURE RESISTANCE, CURRENT, or VOLTAGE
WE WILL USE IT FOR VOLTAGE MEASUREMENTS
Explain the use of the DMM for measurement of voltages. We use DC Volts settings. The knob is set to point to the function and range. The picture shows the DMM set to 20 Volts DC Full Scale Range. That is the range used in ENG 182 Labs.
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21. DIGITAL COUNTER ACCUMULATES AND DISPLAYS ‘COUNTS’
EACH ‘CLEAN’ SWITCH CLOSURE (OR EQUIVALENT) ON THE INPUT CAUSES THE DISPLAY TO INCREMENT BY ONE
RESET DISPLAY TO ZERO WITH FRONT PUSHBUTTON
This is the counter we use in labs. It is complex digital circuitry with a liquid crystal display (LCD). A ‘clean’ switch closure means a closure with no ‘bounce’ that would result in electrical noise spikes. The low speed input (pin 3) accepts closures and is filtered to a max count rate of 20 per second. The high speed input (pin 4) accepts rates to 10,000 per second. Using a switch on pin 4 is not appropriate. Pin 1 (silver mark) is the ground pin. A small front panel button switch will reset the counter to zero. (Also note that a transistor can be used as a switch to effect a count with this unit).
Must be careful with small connector…always handle it by the connector body…NO PULLING BY THE LEADS !!
Pin 1
Silver Mark
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22. SCHEMATIC CIRCUIT DIAGRAMS
TO COMMUNICATE THE DESIGN IN A STANDARD WAY
Standard symbols are used to communicate the circuit design. Here is a simple series circuit. Point out and identify the components. Why is it a series circuit ? (The same current flows through all components). The points AA, BB, EE might be test points for voltage measurements. The symbol with three horizontal lines is the GROUND (GND) symbol. As shown it really means EARTH GROUND but is loosely used to indicate a return path to the power source.
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23. Assignment
Read Lab 3 Procedure Carefully
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