that every connection represented in the schematic diagram is faithfully re-created on the breadboard. For example, the schematic diagram in Figure 6-4 indicates that pin 1 of the 555 timer IC must be connected to ground. Thus, when you build the circuit on a breadboard, you must ensure that this connection is properly made.
One of the first challenges you face when building a circuit on a breadboard is connecting the pins on an integrated circuit. In a schematic diagram, the pin connections on an integrated circuit are rarely drawn in numerical order. For example, in the schematic diagram shown in Figure 6-4, the pin connections on the 555 timer IC are listed in this order, going counterclockwise from the top left: 7, 6, 2, 1, 3, 8, and 4. (Pin 5 is not used.)
But the pins on an actual 555 timer IC chip are arranged in numerical order starting at the top-left corner of the chip, as shown in Figure 6-8. Notice also that there are pins on the left and right side of the chip but none on the top or bottom. (The dot imprinted on the top of the chip is used to identify pin 1.)
FIGURE 6-8: How the pins are numbered on a 555 timer integrated circuit.
You’ll have to use your wits to re-create a circuit represented by a schematic diagram on a solderless breadboard. Here are some pointers to get you started:
Start by designating the top row of bus strips as the positive power supply and the bottom row as the ground. Connect your battery connector to holes in one end of these bus strips, but don’t yet connect the battery; it’s never a good idea to apply power to your circuit before you’ve finished assembling it.
Next, insert any ICs required for the circuit. Insert them so that they straddle the ditch in the middle of the terminal rows and, if your circuit has more than one IC, orient them all the same. You’ll only confuse yourself if pin 1 is on the bottom-left corner of some of your ICs and on the top-right corner of others.
Each pin of each IC is connected to a terminal strip that has four additional connection holes. Thus, you can connect as many as four additional components or jumper wires to each pin. If your circuit requires more than four component connections to a single pin, use a jumper wire to extend the pin’s terminal strip to an unused row anywhere on the breadboard.
Use jumper wires to connect the voltage source and ground pins for each IC to the nearest available connection hole in the voltage and ground buses.
Now work your way around the rest of the pins for each IC, connecting each component as needed. If one end of a component connects to an IC pin and the other end connects to either the voltage source or ground, plug one end of the component into an available connection hole on the terminal strip for the IC pin and plug the other end into the nearest available connection hole on either the voltage supply or ground buses.
If you want, you can trim the leads of the various components so that the parts fit closer to the breadboard. This results in a breadboard circuit that’s neater, and with fewer bare leads sticking up high above the breadboard, the likelihood of leads accidentally coming in contact with each other and creating a short-circuit are less likely. I usually don’t trim the leads, however, unless the circuit is complex enough that I’m not able to keep the component leads away from each other without cutting them down to size.
Assembling the coin-toss circuit on a solderless breadboard
This section presents a complete procedure for assembling the coin-toss circuit on a small solderless breadboard. When you get all your materials together, you should be able to complete this project in about an hour.
All the parts required to build this prototype circuit can be purchased from RadioShack, or you can order them online from any electronic parts supplier. For your convenience, here is a complete list of the parts you’ll need to build this prototype circuit, along with the RadioShack catalog part numbers:
| Quantity | Description |
|---|---|
| 1 | Small solderless breadboard |
| 1 | Solderless breadboard jumper wire kit |
| 1 | LM555 timer IC |
| 1 | 1 kΩ, ¼ W resistor (5 per package) |
| 1 | 10 kΩ, ¼ W resistor (5 per package) |
| 2 | 470 Ω, ¼ W resistor (5 per package) |
| 1 | 0.1 μF polyester film capacitor |
| 1 | Red LED 5 mm |
| 1 | Green LED 5 mm |
| 1 | 9 V battery snap connector |
| 1 | 9 V battery |
You can build this circuit using equivalent parts from any supplier. So if you already have equivalent parts on hand, you don’t need to run out to RadioShack and purchase them just for the sake of spending money.
You won’t need many tools for this project. You can probably assemble it without any tools at all, but you may want to keep your wire cutters, wire strippers, and tweezers handy.
The steps that follow identify specific holes in the terminal strip area of the breadboard using numbers and letters. If you’re using a different breadboard than the one listed in the parts list, you might encounter a different numbering system. If so, you can refer to Figure 6-7 to translate the numbers given in the steps for the breadboard you’re using.
After you have everything you need, follow these steps to assemble the circuit:
Follow these three steps to insert the IC and connect it to power.
1 Insert the 555 timer IC.Take a close look at the 555 timer IC. On the top, notice a small dot in one corner; this dot marks the location of pin 1. Carefully insert the leads of the 555 timer IC into the breadboard near the middle of the board, inserting pin 1 into hole E14 and pin 8 in hole F14. The IC will straddle the groove that runs down the center of the board.
2 Connect pin 1 of the 555 timer IC to the ground bus.Insert one end of a small jumper wire into hole A14 and the other end into the nearest available hole in the bottommost bus strip.
3 Connect pin 8 of the 555 timer IC to the +9 V bus.Insert one end of a small jumper wire into hole J14 and the other end into the nearest available hole in the topmost bus strip.
4 Connect pins 2 and 6 of the 555 timer together.Insert one end of a small jumper wire into hole C15 and the other end in hole H16. The jumper wire will reach over the top of the 555 timer chip.Figure 6-9 shows what the breadboard looks like after these three steps.
The next five steps connect the LEDs and resistors R3 and R4. The LEDs will use the terminal strips in rows 19 and 21.
1 Connect pin 3 of the IC to row 19.Insert
