Soft clay can be shaped a hundred ways, and pressed back into a ball between them. Only the shape worth keeping goes into the fire to harden.
⟨ transmission ends ⟩Twisting wires together is fine for one circuit, but it is slow when we want to try a circuit and then change it. Most builders use a breadboard instead. It is a plastic board full of holes that part legs and wires push into. Some of the holes are joined to each other underneath. Here is a typical one.
A full-size solderless breadboard. Solderless means no solder is needed. Solder is a soft metal that is melted onto two parts to join them permanently.
Parts
- holes
- Push part legs and wires straight in. The holes are 2.54 mm apart, the same spacing as the legs of most parts.
- numbers and letters
- Every hole has a name, its column number and then its row letter, like 12c.
- trench
- The gap down the middle. It splits the rows a to e from the rows f to j.
- power rails
- The long rows along the edges, with a red line for + and a blue line for −. Many full-size boards split each rail in the middle, so check a new board’s rails end to end with the beep.
Boards also come smaller. A mini board like the one below has 17 columns and no power rails, and we will build our first circuit on one.
From above, every hole looks the same, so we cannot see which ones are joined. The multimeter’s continuity beep will tell us. On the bench below, the meter is on continuity and its black probe is in hole 12c. Which holes do you think are joined to it?
On a phone, this bench uses a mini board with 17 columns and no power rails. Two joined holes read 0.1 Ω, and holes that are not joined read OL. The x-ray view draws the metal under the plastic.
Four other holes beeped, all in column 12 on the same side of the trench. Under 12c and those four holes is one piece of springy metal, called a clip. Whatever you push into any of the five holes touches that same clip, so all five are joined.
Sometimes we need the two halves of a column joined. On the next bench the black probe is in 12e, just above the trench, and a short jumper wire is on the bench. Can you use it to make the meter beep with the red probe in 12f?
The meter always shows what the jumper wire joins, wherever you put it. On a full-size board, the rails on this bench run from end to end, with no split in the middle.
Once the jumper wire was in, 12e and 12f were joined, and so were the two clips of column 12. Full-size boards also have power rails along their edges, one for + and one for −. A rail works like one long clip along the board, so a part anywhere along it can reach the battery. On boards that split their rails in the middle, each half is a clip of its own.
Now let’s build our first circuit again, this time on the mini board. The circuit has a 9 V battery, a 470 Ω resistor and a red LED, joined by two jumper wires. The battery’s red lead is already in the board for +, and its black lead for −.
The battery gives 9 V and has about 2 Ω inside it, and it is drawn smaller than the board. Its leads are in column 2, + above the trench and − below it. The clips under the holes in use are drawn so you can see them, which a real board does not show.
Wherever two parts meet, they meet in a clip, as the resistor and the LED did. So when a circuit on a board does not work, we switch the power off and check each place where two parts should meet. With the multimeter on continuity, touch one probe to each of the two legs, and a beep means they are joined.
With red wires for + and black wires for −, it is easy to see which wires carry the battery’s power. Keep the jumper wires short, and push each part down until it sits close to the board. Then no wire hides a leg, and the probe can reach every one of them.
Three questions, if you want to check yourself.
You push an LED’s two legs into 14c and 14d and turn the power on. The LED stays dark. Why?
A resistor’s legs go into 10c and 10h. Does the board join its two legs?
On a full-size board, the battery is joined to the left end of the + rail. An LED circuit at the left end works, but one at the right end gets no power. What do you check first?
Laying out a circuit on a board is much easier with a drawing of it in front of us. In The Schematic we will learn how builders draw a circuit, so that anyone can build it from the drawing.
Lesson 7 done.
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