Make: Electronics by Charles Platt (classic books to read TXT) 📗

as possible to the component and as far as possible from the joint. (You don’t want to suck too much heat away from the joint.)

3. Make sure there is a metal-to-metal connection between the alligator clip and the wire to promote good heat transfer.

Fundamentals

All about perforated board

For the remainder of this book, you’ll be using perforated board whenever you want to create permanent, soldered circuits. There are three ways to do this:

1. Point-to-point wiring. You use perforated board that has no connections behind the holes. Either the board has no copper traces on it at all, as in Figure 3-70, or you will find a little circular copper circle around each hole, as in Figure 3-71. These circles are not connected with each other and are used only to stabilize the components that you assemble.

Point-to-point wiring allows you to place the components in a convenient, compact layout that can be very similar to a schematic. Under the board you bend the wires to link the components, and solder them together, adding extra lengths of wire if necessary. The advantage of this system is that it can be extremely compact. The disadvantage is that the layout can be confusing, leading to errors.

Figure 3-70.

Figure 3-71. Either this type of perforated board or the type in Figure 3-70 can be used for point-to-point wiring in Experiment 14.

2. Breadboard-style wiring. Use perforated board that is printed with copper traces in exactly the same pattern as the conductors inside a breadboard. Once your circuit works on the breadboard, you move the components over to the perfboard one by one, maintaining their exact same positions relative to each other. You solder the “legs” of the components to the copper traces, which complete the circuit. Then you trim off the surplus wire. The advantage of this procedure is that it’s quick, requires very little planning, and minimizes the possibility for errors. The disadvantage is that it tends to waste space. A cheap example is shown in Figure 3-72.

3. You can etch your own circuit board with customized copper traces that link your components in a point-to-point layout. This is the most professional way to complete a project, but it requires more time, trouble, and equipment than is practical in this book.

Point-to-point wiring is like working with alligator clips, on a much smaller scale. The first soldered project will use this procedure.

Figure 3-72. Perforated board etched with copper in variants of a breadboard layout. This example is appropriate for Experiment 15.

Experiment 14: A Pulsing Glow

You will need:

Breadboard

15-watt pencil-type soldering iron

Thin solder (0.022 inches or similar)

Wire strippers and cutters

Plain perforated board (no copper etching necessary)

Small vise or clamp to hold your perforated board

Resistors, various

Capacitors, electrolytic, 100 µF and 220 µF, one of each

Red LED, 5 mm, rated for 2 volts approximately

2N6027 programmable unijunction transistor

Your first circuit using a PUT was a slow-speed oscillator that made an LED flash about twice each second. The flashes looked very “electronic,” by which I mean that the LED blinked on and off without a gradual transition between each state. I’m wondering if we can modify this circuit to make the LED pulse in a more gentle, interesting way, like the warning light on an Apple MacBook when it’s in “sleep” mode. I’m thinking that something of this sort might be wearable as an ornament, if it’s small enough and elegant enough.

I’m also thinking that this first soldering project will serve three purposes. It will test and refine your skill at joining wires together, will teach you point-to-point wiring with perfboard, and will give you some additional insight into the way that capacitors can be used to adjust timing.

Look back at the original circuit in Experiment 11, on page 82. Refresh your memory about the way it worked. The capacitor charges through a resistor until it has enough voltage to overcome the internal resistance in the PUT. Then the capacitor discharges through the PUT and flashes the LED.

If you drew a graph of the light coming out of the LED, it would be a thin, square-shaped pulse, as shown in Figure 3-73. How can we fill it out to make it more like the curve in Figure 3-74, so that the LED fades gently on and off, like a heartbeat?

Figure 3-73.

Figure 3-74. The original PUT oscillator circuit in Experiment 11 made the LED emit sharp, short flashes. The upper graph shows what we might find if we measured light output over time. The second graph shows a gentler onset to each flash, followed by a slow fade-out. Capacitors can be used to create this effect.

One thing is obvious: the LED is going to be emitting a greater total amount of light in each cycle. Therefore, it’s going to need more power. This means that C1, in Figure 3-75, must be a larger capacitor.

When we have a larger capacitor, it takes longer to charge. To keep the flashes reasonably frequent, we’ll need a lower-value resistor for R1 to charge the capacitor quickly enough. In addition, reducing the values of R2 and R3 will program the PUT to allow a longer pulse.

Most important, I want to discharge the capacitor through a resistor to make the onset of the pulse gradual instead of sudden. Remember, when you have a resistor in series with a capacitor, the capacitor not only charges more slowly, but discharges more slowly.

Figure 3-75 shows these features. Compare it with Figure 2-103 on page 85. R1 is now 33K instead of 470K. R2 and R3 are reduced to 1K. R4 also is 1K, so that the capacitor takes longer to discharge. And C1 is now 100 µF instead of 2.2 µF.

Figure 3-75. The first step toward creating a gentler flashing effect is to use a larger capacitor for C1 and discharge it through a resistor, R4. Lower-value resistors are necessary to charge the capacitor rapidly enough.

R1: 33K

R2: 1K

R3: 1K

R4: 1K

C1: 100