Fun with solderless breadboards
When building a circuit for the first time, it is often very useful
to have a way to quickly change connections or parts placement.
In the early days of electronics, quick, temporary circuits were
sometimes built on a piece of wood, similar to the boards that
bread is sliced on. Building a first prototype came to be known
as
breadboarding.
Back when components like tubes and transformers were large and
long wires were common, it was easy to solder and unsolder connections.
Modern circuits, made with small transistors or many legged integrated
circuits, are much harder to solder and especially to unsolder.
To make life easier, solderless breadboards were invented.
These are blocks of plastic with holes into which wires can be inserted.
The holes are connected electrically, so that wires stuck in the
connected holes are also connected electrically.
The connected holes
are arranged in rows, in groups of five, so that up to five parts can
be quickly connected just by plugging their leads into connected holes in
the breadboard. When you want to rearrange a circuit, just pull the
wire or part out of the hole, and move it or replace it.
Click on photo for a larger picture
In the photo above, we have a complete radio, with an antenna coil, a tuning
capacitor, a three-legged integrated circuit, a battery, and earphone, two
resistors, and three capacitors. This radio is the Three Penny Radio kit
from the
Scitoys Catalog, which is usually soldered, using three pennies as
convenient places to connect the various parts.
The three-penny radio needs these parts:
- An antenna coil
You can wind one by hand, but in this project we use a much
smaller coil with a ferrite rod inside, from our
catalog.
- An MK484-1 AM Radio Integrated Circuit
This is the heart of the radio. We carry it in our
catalog.
- A Piezoelectric earphone
Also in our
catalog.
- A tuning capacitor
We use a variable capacitor, from 0 to 160 microfarads.
We have it in our
catalog.
- A 100,000 ohm resistor
This resistor will have four colored bands on it.
The colors will be brown, black, yellow, and gold.
- A 1,000 ohm resistor
This resistor will also have four colored bands on it.
The colors will be brown, black, red, and gold.
- A 0.01 microfarad capacitor
This capacitor will be marked something like ".01M" or "103".
- Two 0.1 microfarad capacitors
These capacitors will be marked something like ".1M" or "104".
- A 1.5 volt battery
- A 1.5 volt battery holder
And, in this version:
- A solderless breadboard
Also in our
catalog.
and later:
- A printed circuit board
Also in our
catalog.
Click on photo for a larger picture
In the closer view, you can see that the parts we want to be electrically
connected are plugged into one of the five holes marked A, B, C, D, or E,
(or in this case, where we used the second half of the board, marked
F, G, H, I and J) in rows marked 1 through 63.
Along each side of the breadboard are two strips of power supply rails,
making it convenient to connect a battery when many parts need power.
In our simple radio, only one part needs power, so it is convenient
to simply plug the battery wires directly into the main circuit area.
The solderless breadboard is designed to accept the leads from parts such as
resistors, integrated circuits, transistors, and other parts with round
solid wire for leads. Some of the parts for the radio have thin, stranded
wire that is not stiff enough to poke into the holes, or (like the variable
capacitor) have flat strips of metal that are too big to fit into the holes.
For these parts, we solder their leads to pieces of wire cut from the leads
of other parts, such as resistors or capacitors. Most such parts have leads
that are longer than we needed anyway, so they will fit more snuggly onto
the board with shorter leads. In the photo you can see that the antenna
coil, the variable capacitor, and the piezoelectric earphone have wires
soldered to their leads to make it easy to plug them into the breadboard.
Click on photo for a larger picture
Having the holes arranged in a labeled grid is convenient for describing the
parts layout. We can list each part, and the letter and number of each lead:
- Antenna coil: J9 and G16
- Tuning capacitor: F9 and F16 (only the two rightmost leads are used)
- MK484 IC: H15, H16, and H17 (flat side facing row G)
- 100,000 ohm resistor( brown, black, yellow): I9 and J17
- 1,000 ohm resistor (brown, black, red): I17 and I20
- 0.01 microfarad capacitor (marked 103 or .01M): G9 and G15
- 0.1 microfarad capacitor (marked 104 or .1M): F15 and F17
- 0.1 microfarad capacitor (marked 104 or .1M): F17 and F22
- Piezoelectric earphone: F20 and F22
- Negative battery wire (black): J15
- Positive battery wire (red): J20
This makes it very simple to build the circuit, and easy to double check
all of the connections.
Making the circuit permanent
Solderless breadboards are great for building circuits the first time,
and getting them to work, or experimenting with design changes. But when
you get the circuit working the way you want it to work, you will want to
copy it to a more permanent form, by soldering it onto a circuit board.
The printed circuit boards we carry in our
catalog
also have five holes
that are electrically connected. The holes are grouped into 3 holes and
2 larger holes, to make it convenient to connect larger wires leading out
from the board, for power connections and other external parts.
The radio shown below was built by a student as a first exercise in soldering:
Here is the back side:
It worked the first time!
Next:
A simple audio amplifier.
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Simon Quellen Field
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sfield@scitoys.com
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