Electronics All-in-One For Dummies. Doug Lowe

Electronics All-in-One For Dummies - Doug Lowe


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6-2: A hand-drawn sketch for an electronic coin tosser.

      After you have an idea for a project, the next step is to design a circuit that meets the project’s needs. At first, you’ll find it very difficult to design your own circuits, so you’ll turn to books like this one or to the Internet to find other people’s circuit designs. With a bit of Google searching, you can probably find a schematic diagram that’s very close to what your project needs.

      In many cases, you won’t be able to find exactly the circuit you’re looking for. You may find a circuit that’s close, but you may need to make minor modifications to make the circuit fit your project’s needs. At first, making modifications to a circuit may seem beyond your abilities. But as you gain experience, you’ll find yourself tweaking circuits all the time to fit specific applications.

       A circuit to detect when someone has entered the room to trigger the prop’s action

       A circuit to open and close the jack-in-the-box

       A circuit to time how long the jack-in-the-box should stay open

       A circuit that plays a screaming sound

       A circuit that provides a 30-second delay before the prop is activated again

      The schematic diagram shown in Figure 6-3 differs from our project’s needs in just two ways. First, it doesn’t have an on/off switch. And second, it uses a push button instead of the user’s fingers to start and stop the LEDs from flashing.

      Remember Please don’t worry at all if you don’t understand how the circuit depicted in Figure 6-4 works. I wouldn’t expect you to at this point in the book! Understanding how a circuit works and building that circuit are two entirely different things; you can (and probably will) build plenty of circuits whose operation you don’t understand. The only thing you should focus on at this point is how the schematic diagram indicates the various connections between the parts in the circuit. You learn the details of how this circuit works in Book 3, Chapter 2.

      One final step you might want to consider when designing a circuit is to create a final version of the schematic diagram that indicates what components will be mounted on your final circuit board and what components won’t be on the circuit board. This diagram will come in handy later when you’re ready to create the circuit board that will become the permanent home of your circuit.

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      FIGURE 6-3: A schematic diagram for a simple coin-toss circuit.

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      FIGURE 6-4: The schematic diagram for the coin-toss circuit after it has been modified a bit for our project.

Part ID Description
R1 1 kΩ, ¼ W resistor
R2 10 kΩ, ¼ W resistor
R3 470 Ω, ¼ W resistor
R4 470 Ω, ¼ W resistor
C1 0.1 μF capacitor
LED1 5 mm red LED
LED2 5 mm green LED
IC1 555 timer IC
SW1 Momentary-contact, normally open push button
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      FIGURE 6-5: A schematic diagram that indicates which components are on the main circuit board and which aren’t.

      Before you commit your circuit to a permanent circuit board, you want to make sure it works. The easiest way to do that is to build the circuit on a solderless breadboard. The solderless breadboard lets you quickly assemble the components of your circuit without soldering anything. Instead, you just push the bare wire leads of the various components you need into the holes on the breadboard and then use jumper wires to connect the components together.

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      FIGURE


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