breadboard primer - portland community collegespot.pcc.edu/~dgoldman/labs/eetdig-1-0.pdfdavid...

David Goldman, Portland Community College 12000 SW 49th Ave., Portland, OR 97219

Breadboard Primer

Experience

No previous electronics experience is required.

Objective

A solderless breadboard (or protoboard) is a building platform for rapid circuit development. This lab guides you through the process of assembling and testing the simple circuit shown inFigure 1. It's a light controller; it turns on and off lights in what will become a particularly important pattern as you learn more about electronics. Other important skills used in electronics are also introduced:

• Taking continuity measurements

• Understanding how the holes in breadboards are electrically connected

• Identifying and placing DIP chips, jumper wires and through-hole resistors

• Hooking up a power supply for digital circuits.

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Figure 1: Breadboard drawing made using an open-source tool from fritzing.org

http://fritzing.org/welcome/


Equipment

• Breadboard (x1) and assorted wire• Electrical bench equipment (DMM, Power Supply and ARB)• Test probe cables (x2 banana plugs to alligator clips)• Text probe cable (x1 coaxial to push clips)• 74193 IC (x1)• 470 ohm resistors (x4)• LEDs (x4)

Procedure 1: Check the Breadboard

Configure Equipment for a Continuity Check

A simple check to determine if two points are electrically connected (have very little resistanceto electrical conduction) is called a continuity check. This check can be useful to find broken wires or to find a particular wire in a large bunch. To demonstrate a continuity check let's configure a piece of bench equipment call a Digital Multimeter (commonly called a DMM) to perform a continuity check.

Identify the DMM at your bench, it should look something like Figure 2.

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Figure 2: Fluke 8808A Digital Multimeter (DMM)


If it is not already on, turn it on now by pressing the green power button in the lower right corner. Some numbers and symbols should appear on the screen.

Now let's configure it to measure continuity.

The continuity button (shown on the left) has a symbol meant to represent sound waves moving from a point. There is another symbol just below the continuity symbol,but this is for a different functionality, which is not used in this lab. Find and press the

button until the continuity symbol appears on the display.

Next you'll need a pair of probe cables. Figure 3 shows two types of cable ends called banana plugs and alligator clips. For the continuity check one end of the cables should have banana plugs. The other end should have alligator clips (if you don't find alligator clips, other types may work just as well). Connect the banana plugs to the DMM's HI and LO inputs (they are the top left and middle left inputs on Figure 2).

Notice that when you touch the metal of the two alligator clips together the equipment makes a beep. This indicates that there is very little resistance between the probes, which is reasonable since the probes are touching.

Try putting the probes on either end of a piece of wire. Hear the beep? As you experiment a little, you should get the idea. Next, let's use this setup to check the internal connections in the breadboard.

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Figure 3: Test probe cable ends, alligatorclips (left) and banana plugs (right)


Checking Breadboard Continuity

Create a sketch of your breadboard (Figure 4) and draw dots to represent holes in the board. Now do a continuity check between various holes. (Depending on your probe ends you may use wires to help—for example put one end of a wire in a alligator clip and ‘probe’ with the other end of the wire.) If there is continuity, draw a line between the dots (connect the dots!) on your sketch. You are building a map of your breadboard.

An understanding of the internal connections on your breadboard is important, but you are also checking the board for defects. If you happen to find a defect on your board, make a note, so you can avoid this area of the breadboard in the future.

With your continuity map completed, do you notice any patterns? Make a brief comment about your results. Did you find 4 long connected lines running the length of the board? Theselong lines can be called rails and are commonly used to hookup power and ground. Keep the rails in mind for the next procedure.

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Figure 4: Breadboard


Procedure 2: Build the Circuit

Place the Chip

A computer chip is a collection of tightly packed circuits embedded in a black plastic case. Access to the circuits inside is through metal leads (or pins) that extend from the edges. There are many different package styles, but in this lab you will use a style used for breadboards. It is called dual-inline package (DIP) and has an even number of pins that project from the sides and bend down (see Figure 5). DIPs are also known as through-holes, since they are designed to be inserted through holes in a printed circuit board.

The ‘top’ of the chip is identified with a notch (or sometimes an indented or painted dot). Figure 6 shows a 16-pin chip drawing with a notch at the top.Identifying the top is important because pins are commonly referred toby number. Pins are numbered beginning with 1 at the top left andcontinues counter-clockwise around the chip (as shown).

As a general rule, place your chips with the top of the chip toward thetop of the breadboard—this can simplify troubleshooting later. Alwayscheck that the chips are oriented correctly. An ‘upside-down’ chip mayreverse the power connections (depending on the chip), which maydestroy or damage the chip or breadboard.

For this lab you will need to find a chip called a 74193. This number iswritten on the chip and can usually be found embedded with someletters. There are also symbols, codes and other markings on the chip,but what follows is a typical format (Figure 7).

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Figure 5: 18-pin DIP chip example

Figure 6: Pin numbering

notch


In the example image (Figure 8), SN and the logo identify the manufacturer as Texas Instruments. LS stands for Low Power Schottky (a particular speed and power consumption) and N stands for DIP, in this case. The 74 and 193 identify the family (TTL) and logic, respectively. You will learn more about the functionality of this chip later on in the lab.

Find a 74193 from your kit and set it notch side ‘up’ on the breadboard (in the Figure 9 the notch is on the left since the breadboard is rotated 90 degrees counter-clockwise from ‘up’).

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Figure 8: Chip labeling example

Figure 7: 7400 series chip identification guide


Notice the chip straddles the center groove of the breadboard. (This groove is designed to accommodate a placement or extraction tool, but if you don’t have one, just use your fingers.) Make sure the pins are aligned with holes in the breadboard and press the chip into place. Press it all the way down until the plastic body of the chip is in contact with the breadboard.

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Figure 9: Chip on breadboard


Connect the Jumpers

A jumper is a small piece of wire that connects two parts of a breadboard. For this part of the lab you will need 5 small pieces of wire to serve as jumpers. These may be part of a kit with solid-stranded wire or you may have to cut a few from the wire cutting station in the lab.

Use the shortest piece of wire you can for each particular connection. (Even better is to find the shortest wire that will be flush with the surface of the breadboard.) Later you will learn howlong wires can disrupt the function of your circuit. Most importantly for the moment: shorter wires will make your circuit significantly easier to build, troubleshoot and repair.

From the breadboard continuity exercise you known that breadboards have rails. This circuit will use two rails—a red rail (at the top of Figure 10) and a blue rail (on the bottom of Figure10). Through the rest of this lab, let’s refer to the red rail as the positive rail and to the blue railas the negative rail.

Now make the following connections (use Figure 10 to assist you):• Pin 5 to Pin 16• Pin 8 to the negative rail• Pin 11 to the positive rail• Pin 14 to the negative rail• Pin 16 to the positive rail

Now to add lights...

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Figure 10: Chip with jumpers in place


Connect the LEDs

A light emitted diode (LED) is a componentthat glows when a limited amount of currentpasses through it in one particular direction.The positive terminal is called an anodeand the negative terminal is called acathode (Figure 11).

Find 4 red LEDs from your kit. Notice theLEDs have one lead longer than the other—the longer lead is the positive lead or theanode. Also, if the LED is clear enough youmay be able to see the anvil and postshapes identified in Figure 11.

For this circuit each cathode will beconnected to its own 5 hole 'row' and all theanodes will be on a rail—in this case thepositive rail.

Remember which leads should beconnected to positive and which to negativeand then insert the 4 LEDs.

An example is shown in Figure 12, but you can use any available breadboard rows. In Figure12 the LEDs have 5 empty rows between them, but you may find it easier to build with only one empty row between each LED.

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Figure 12: LEDs in place

Figure 11: LED diagram from wikimedia.org

http://commons.wikimedia.org/wiki/File:LED,_5mm,_green_(en).svg


In the next section, the LEDs will connect to the chip through resistors.

Connect the Resistors

Resistors are electrical components that resist the flow of current in a circuit. Resistors come in different package styles, but the most common for breadboards is a through-hole type, a cylindrical shape with metal leads projecting from either side (also known as an axial-lead). A few of this type are shown in Figure 13.

Notice that each resistor has colored stripes. These indicate the amount of resistance it provides—also known as the value of the resistor. Units of resistance are called ohms, indicated with a greek letter, the upper-case omega (Ω).

There can be 3, 4 or 5 color bands on a resistor, but most resistors in your kit (and in the lab) have 4 color bands. With 4 color bands the first 3 indicate the value and the fourth indicates the tolerance (the error between the actual value and the color band value). The colors gold and silver are reserved to indicate tolerance.

To determine the resistance value from the color bands, start reading the colors from the band

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Figure 13: Various axial-lead resistors


closest to the edge or the opposite side from the tolerance band. To translate the colors to a value use Figure 14.

Here is a simple procedure to determine the value: write the first two numbers, then write the number of zeros (or additional zeros) given by the third.

Some examples:• brown (1), black (0), red (2 additional zeros) equals 1000 Ω, which should be written

as 1k Ω• red (2), red (2), black (0 zeros) equals 22 Ω

At this point, determine (and record) the resistance for each of the different types of the resistors in your kit.

For this lab you’ll need four 470 Ω resistors. The resistors should be placed as shown and jumper wires can be used to connect to the chip. Note that from left to right the resistors are placed in Pins 3, 2, 6, 7, as shown in Figure 15.

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Figure 14: Part of a resistor color chart from wikipedia.org


Complete the Circuit

Finally complete the circuit with some more jumpers to use for external connections. The external connections are power (Pin 16; red wire), ground (Pin 8; black wire) and a signal (Pin4; yellow wire) in Figure 16.

Now let’s connect an input signal.

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Figure 15: Circuit with 4 resistors

Figure 16: Circuit with external connection wires


Connect the ARB

For this lab a square wave pulse is used to change the LED patterns. This pulse is generated from an Arbitrary Waveform Generator (ARB). Identify this equipment at your bench. (Figure17)

Also you’ll need a cable with a BNC coaxial connector (sometimes referred to as a Bayonet Nut Connector) on one end and two clips on the other (see Figure 18). The instructor will helpyou configure the ARB for this lab.

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Figure 17: ARB

Figure 18: BNC to alligator clip cable


Next, let's take a closer look at the power supply.

Configure the Power Supply

Identify the analog Power Supply at your bench. It has two analog meters on the faces shownin Figure 19

Unplug any probe cables that may be attached to the Power Supply.

The upper left knob labeled “METER” should be set to “+6 V”. If it is not, turn the knob so it is.

Switch the power supply ON by flipping the “LINE ON” toggle switch up—the meter needles may move.

The meter on the left is labeled “VOLTS” and has two ranges: one from 0 to 25 and another from 0 to 7. For this lab look at the range from 0 to 7 on the bottom of the meter.

Turn the dial on the lower left labeled “VOLTAGE”. As you do you will see the meter needle onthe left move. Use this knob to adjust the needle so that it is aligned with the number 5 (remember to use the 0 to 7 range). This sets the output voltage of the Power Supply to about+5 volts.

Plug the banana ends of the probe cables into the Power Supply as shown in Figure 20, but don’t attach the other ends to the circuit yet. Also, avoid having the probe cables touch each other.

The +5 V Power Supply configuration is shown in Figure 20.

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Figure 19: Power supply


STOP: Have the lab instructor review your setup and circuitbefore you continue.

Connect the Power Supply

• Switch off the power supply.• Connect the cable connected to the ‘+6 V’ terminal on the power supply to the power

rail of the circuit. And connect the ‘COM’ terminal on the power supply to the ground rail of the circuit.

• Switch on the power supply.

Are the LEDs turning on and off in a sequence? If so, congratulations! If not, your instructor will assist you in troubleshooting your circuit and setup.

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Figure 20: Power supply on with probes attached


Procedure 3: Test the Circuit

Test the Circuit

A) Record the sequence of the LEDs in your lab notebook.

B) Using the wall clock estimate how long it takes the cycle to repeat.

C) Label each of the 4 LEDs with A, B, C, D. How long is each LED off and then on for?

D) Record what happens when you swap the connection at Pin 4 and Pin 5.

Analysis:

A) How would you describe the pattern of LEDs in this lab? What could you do with these lights?

B) Complete the lab with a conclusion in your lab logbook. Record what you did, any problems you encountered and how you solved them. Also describe what you learned from this lab.

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breadboard primer - portland community collegespot.pcc.edu/~dgoldman/labs/eetdig-1-0.pdfdavid...

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