Download GK-12 Breadboard Tips and Techniques for Digital Circuit

GK-12 Sensors! Breadboard Tips and Techniques for Digital Circuit Construction
The Bread-Board
Figure 1
The Structure of a Breadbroad
A breadboard, shown above, is a plastic shell with connections that connect certain parts
of the breadboard together underneath the shell. The breadboard here is mounted on a
metal frame for support.
Interconnections
The square “holes” that are visible are where electronic parts can be inserted. In the
above picture, there are two set of 64x5 grids. Each column of 5 running vertically above,
are connected together. For example, the green wires above are inserted at one end of
columns, while the LEDs are inserted at the other end of the column. There are
interconnections under the plastic shell that connect the green wires to the LED. The ease
with which electronics parts can be connected together is why breadboards are invaluable
for circuit prototyping.
Power Connectors
The Black and the Red connectors that can be seen in the upper right corner are
connectors that can be used to connect different power supplies. The “screw cap” can be
unscrewed to reveal a metal platform with a hole in it. A wire can be inserted into the
hole and the “screw cap” screwed down to clamp it tight. The power and ground cables
of a 9V battery connector can be inserted along with the wires going to the breadboard.
The screw cap can be screwed down to ensure a firm connection.
Power Rails
In addition to the two sets of 64x5 grids of holes, there are also two rows running across
the top and bottom of the breadboard. These are the power rails. Power rails are
connected together in rows rather than in column. For example, the red wire coming
down from one of the power connector connects the entire row. The black wire from the
other connector connects the other row. However, notice that the power rails are split at
the center. There are no internal connections between the right five “blocks” of the power
rail with the left five “blocks” of the power rail. In order to connected, both sides of the
power rails, a “jumper” wire has been used to connect the right and left power rails.
Using these wires, power can be provided on end of the breadboard to components
plugged at the other end of the breadboard. Note that the bottom power rails are also split
at the center. If the entire rows are to be used they need to be connected by a jumper wire
also. In addition, jumper wires from the top rails must be connected to the bottom rails,
otherwise there will be no power on the bottom rails.
Voltage Regulator/Transformer 5 Volt Connector
Figure 2
Although the power connectors described above can be used for delivering power, for
digital circuits this modified part must be used. The need for this part arose because
unregulated transformers were purchased to power digital circuits. These transformers are
labeled as outputting 5 Volts, however, they really output 8 Volts with a small load
attached. As the load increases and more current is drawn, the voltage decreases.
However, this voltage swing is not desirable in many circuits. The modified part shown
above is a 5 Volt regulator hot-glued to a power connector for the transformer. The 5
Volt regulator needs to be used for digital circuits. Using any other voltage will damage
the digital parts. The reason these parts were connected together was to prevent the use of
the transformer directly without the voltage regulator. The two leads of the regulator are
ground (center) and power (right). This part can be inserted into the breadboard, and the
transformer snapped into the connector for easy 5 Volt delivery. This part can be seen in
use on the breadboard above.
Dip-Switch/Resistor Network Pack Circuit for Input
Figure 3
Figure 4
Figure 5
This circuit provides an easy way of inputting values to a digital circuit. The Dip Switch
is the red component and the Resistor Network Pack is the blue component. The Resistor
Network Pack shown also in Figure 4, has a pin configuration that must be followed. The
side of the resistor pack with the print is the “front.” At the far left end of the component
a black circle can be seen in Figure 4. This pin must be connected to the power supply.
The other pins do not required to be connected to power. The circuit in Figure 3 depicts
how the red wire used for power is connected to the “power pin” on the resistor pack.
Notice in Figure 3 how the rightmost pin of the resistor pack is connected to switch 8 of
the dip switch. This is the recommended configuration.
Notice also how the dip-switch “straddles” the gap running the length of the breadboard.
In this way, the dip switch can now connect or disconnect two different columns. Notice
also how a jumper wire is used to connect the ground rail at the top of the breadboard to
the ground rail at the bottom of the breadboard. Remember that there is no connection
between the top and bottom rails.
Once the dipswitch and resistor pack is placed on the board, the next thing that needs to
be done is to connect wires from all the columns connected to the dip-switch to the
ground rail. This way one side of the dip-switch is “tied” to ground.
The dip-switch can now be used to “input” values. When the switch is pushed to one side
it disconnects the top column from the bottom column on the breadboard. Voltage
appears on the column due to the pin of the resistor pack pin connected to that column.
When switch is pushed to the other side, the dip-switch connects the top column to the
bottom column. Since the top column along with the pin of the resistor pack is “tied” to
ground, no voltage appears on the top column.
The dip-switch circuit can be tested to ensure correct operation.
1) Use green wires and connect dip-switch 7 and connect to another column
elsewhere on the breadboard.
2) Insert the long end of an LED into the same column as the green wire.
3) Connect the short end of the LED to the ground rail.
4) Plug in the transformer into a wall socket.
5) Push switch 7 to one side, then the other side. The LED should turn on when the
switch is pushed to one side and off when pushed to the other side. The dip-switch
is labeled ON, on one side. This ON indicates that the switch is closed or it is
connecting one side to the other side. This will result in the LED going off. This
may cause confusion, but it should be noted that the ON on the switch indicates
the opposite of the state of the LED.
The idea of the dip-switch is that when the dip switch is open, or there is no connection
between the top and bottom column, current flows from the resistor pack to the electrical
component. However, when the dip-switch is closed, or the top and bottom column are
tied together, current flows from the resistor pack to ground rather than to the electrical
component. The LED does not turn on because there is no current flowing through it.
This resistor-pack/dip-switch circuit should be placed as far to the left side of the
breadboard as possible to leave space for other components.
Logic Gates
Each GK-12 Electronic Kit contains a series of logic gates. The pin diagrams of each of
the gates are available on the kits themselves. Note that usually pin 7 in Ground and pin
14 is power (5 Volts).
The proper way to utilize a logic gate is to insert in such that it “straddles” the top and
bottom grids. The pins on each side of the gate can be used to input and output up to six
different values.
The following figures depict the correct construction of logic circuits.