Breadboard Primer. Experience. Objective. No previous electronics experience is required.

Transcription

1 Breadboard Primer Experience No previous electronics experience is required. Figure 1: Breadboard drawing made using an open-source tool from fritzing.org 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 in Figure 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. 1 of 16

2 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) 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 resistance to 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. Figure 2: Fluke 8808A Digital Multimeter (DMM) 2 of 16

3 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). Figure 3: Test probe cable ends, alligator clips (left) and banana plugs (right) 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. 3 of 16

4 Checking Breadboard Continuity Figure 4: Breadboard 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? These long lines can be called rails and are commonly used to hookup power and ground. Keep the rails in mind for the next procedure. 4 of 16

5 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. notch Figure 5: 18-pin DIP chip example 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 to by number. Pins are numbered beginning with 1 at the top left and continues counter-clockwise around the chip (as shown). As a general rule, place your chips with the top of the chip toward the top of the breadboard this can simplify troubleshooting later. Always check that the chips are oriented correctly. An upside-down chip may reverse the power connections (depending on the chip), which may destroy or damage the chip or breadboard. For this lab you will need to find a chip called a This number is written on the chip and can usually be found embedded with some letters. There are also symbols, codes and other markings on the chip, but what follows is a typical format (Figure 7). Figure 6: Pin numbering 5 of 16

6 Figure 7: 7400 series chip identification guide Figure 8: Chip labeling example 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 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 ). 6 of 16

7 Figure 9: Chip on breadboard 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. 7 of 16

8 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 how long 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 Figure 10). Through the rest of this lab, let s refer to the red rail as the positive rail and to the blue rail as 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 Figure 10: Chip with jumpers in place Now to add lights... 8 of 16

9 Connect the LEDs A light emitted diode (LED) is a component that glows when a limited amount of current passes through it in one particular direction. The positive terminal is called an anode and the negative terminal is called a cathode (Figure 11). Find 4 red LEDs from your kit. Notice the LEDs have one lead longer than the other the longer lead is the positive lead or the anode. Also, if the LED is clear enough you may be able to see the anvil and post shapes identified in Figure 11. For this circuit each cathode will be connected to its own 5 hole 'row' and all the anodes will be on a rail in this case the positive rail. Remember which leads should be connected to positive and which to negative and then insert the 4 LEDs. Figure 11: LED diagram from wikimedia.org An example is shown in Figure 12, but you can use any available breadboard rows. In Figure 12 the LEDs have 5 empty rows between them, but you may find it easier to build with only one empty row between each LED. Figure 12: LEDs in place 9 of 16

10 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. Figure 13: Various axial-lead resistors 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 10 of 16

11 closest to the edge or the opposite side from the tolerance band. To translate the colors to a value use Figure 14. Figure 14: Part of a resistor color chart from wikipedia.org 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 of 16

12 Figure 15: Circuit with 4 resistors 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 (Pin 4; yellow wire) in Figure 16. Figure 16: Circuit with external connection wires Now let s connect an input signal. 12 of 16

13 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. (Figure 17) Figure 17: ARB 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 help you configure the ARB for this lab. Figure 18: BNC to alligator clip cable 13 of 16

14 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 shown in Figure 19 Figure 19: Power supply 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 on the 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 of 16

15 Figure 20: Power supply on with probes attached STOP: Have the lab instructor review your setup and circuit before 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. 15 of 16

16 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. 16 of 16