In this laboratory project a simple electronic keyboard will be constructed using an integrated circuit. Most modern consumer electronics use a wide variety of integrated circuits (also called ICs or chips). Integrated circuits are electronic components in which a large number of discrete devices such as transistors, diodes, and resistors are miniaturized and combined into a single compact package. Each integrated circuit is designed to perform a function which the individual discrete devices could not do alone. The integrated circuits then form the building blocks of more complicated products. In this lab we will be using the LM324 integrated circuit, produced by National Semiconductor Incorporated.
While ICs contain a great deal of internal components they still require some external circuitry to operate. Often the IC provides a general capability, and the external circuitry customizes the operation to a specific situation. This is the case for our keyboard project. Starting with the basic chip we will add some external components to create the specific circuit we desire.
In building the keyboard we will use a printed circuit board. A printed circuit board is used as the base for the mounting and interconnection of electronic components in all commercial electronics devices. All manufactured electronics from the personal computer to the TV remote control use this technology. The circuit board is made by drawing the connections between desired points in the circuit and then removing unwanted copper by a chemical etching process. In a manufacturing setting the production of circuit boards is a highly automated process. In our case the circuit boards will be hand-made, but the same procedures will be used as in a manufactured circuit board.
After making the circuit boards, we will solder the components into place. Soldering is a humble yet important aspect of electronics. Solder itself is a mixture of the metals tin and lead. It has the property that it melts at a relatively low temperature compared to other metals. Solder is used to make permanent electrical connections.
This project has three parts. The circuit board is made in Part I. Part
II involves building the base for the keyboard. The base is a wooden platform
that contains the "keys" or switches that activate various tones, and provides
a mounting surface for the circuit board, speaker, and battery. In Part
III circuit board is attached to the base and the keyboard is assembled
Part I: THE CIRCUIT BOARD
Part IA: Drawing the pattern:
Position the circuit board as shown in Figure 1. For easier reference remove the pages of the lab containing Figures 1 to 5. Turn the board so the copper side is facing up. Make sure your board is oriented in the same way as the one in Figure 1.
Using the permanent marker, connect the holes as shown in Figure 2. Follow the pattern carefully if the wrong points are connected, the circuit will not work. . First start by drawing a small circle around each hole. Be careful to keep adjacent lines from touching.
In the last part of this step the lines are made wider. Continue to
make sure that adjacent lines do not touch. This may be difficult to do
in some places. If you have an accidental overlap, the easiest way to fix
it is to let the ink dry and then scrape the unwanted ink away with a knife
blade. After this step, the ink should cover as much of the board as possible
to reduce the amount of copper that has to be etched away (except of course
for the space needed to keep the connections separate.) Refer to Figure
3 for an example of how you board should look after this step. The ink
should be thick, avoid thin spots with copper showing through. Write your
name or other identifying mark in the open space to aid in later identification.
Etching will take 20 minutes. It will be obvious when the copper has
been removed. The plastic will be visible on the marked side of the board.
In this part, the electronic components will be installed on the circuit board. All components go on the side opposite the copper. A note on terminology: The side without the copper is called the "component side" of the board. The components such as the resistors are mounted on this side. The component wires (called "leads") stick through the holes and are soldered on the copper side. The locations of the various components are shown in Figure 4. The zig-zag lines represent resistors.
There are a few additional components: A 14-pin socket to hold the integrated circuit, a 0.1mfd capacitor (small green, orange, or burgundy object, looks like a tic-tac or cough drop with two wires) and a photocell (flat orange and white disk with two wires). It will be useful to tape these to the Figure 5 sheet. There are also 8 black and white variable resistors (also called potentiometers, a black disk on top with 3 wires). The potentiometers do not need to be taped to the sheet.
Note on how to read resistor colors. The majority of the components
are resistors. These are the small brownish cylindrical objects with colored
stripes. The resistors are used to control either the voltage or the amount
of current flowing in a particular part of a circuit. Resistance is measured
in ohms. Typical resistors are several thousand ohms. A thousand ohms is
abbreviated using the symbol K. For example a 1000 ohm resistor is often
written as 1K. Resistors are coded with bands of color to identify their
resistance. There are usually 4 bands. In all of the resistors used
the last band is gold colored for our purposes this last gold band can
be ignored. This is used to indicate the quality of the resistor and
can be ignored for our purposes. It is only the first three bands that
we have to worry about. The colors are assigned the following numbers:
The first two colors are used to find the first two digits in the value,
and the last is used to determine the number of zeros following those digits.
For example: Green, Brown, Red is: 5, 1, and 2 zeros or 5100 ohms.
Use Figure 4 to locate the holes for the battery connector. Make sure you put the red and black wires in the proper holes. Bend the wires down to touch the copper. All components go on the side opposite the copper. Use a piece of tape on the component side if needed to hold the component in place.
How to solder: To solder touch the tip of the iron to both the
wire and the copper. Wait about 5 to 10 seconds for both pieces of metal
to heat up. Touch the solder to the copper and the pin. Remove the tip
of the soldering iron and let cool. The solder should flow smoothly and
make contact with both metals being joined.
The board measures 7 1/4 inches by 8 inches. With the 8 inch side facing you mark the spots for the tacks that hold the keys and the connecting wire. If possible try to avoid "knots" in the wood as it is difficult to drive nails or tacks into these "knots." Draw a line along the 8 inch side at a distance of 1/2 inch from the edge. This will be the location of the connecting wire. Draw another line at a distance of 2 and 1/8 inches from the edge. This line will be used to locate the tacks holding the keys. Refer to the sample keyboard photograph on the first page if you are unsure about this step.
Obtain 9 brass strips. BE CAREFUL THE EDGES ARE SHARP. Use sandpaper to smooth out the edges. This step is very important. An efficient way to do this is to put the sandpaper down flat on the bench top rough side up. Then hold the brass and rub the edges against the sandpaper. When done set the keys aside.
Locate a 15 inch piece of gray wire remove all of the insulation from the wire. This will be used to connect all of the keys together. To remove the insulation, try removing some of the insulation from one end of the wire, hold this end with a pair of pliers, then slide off the rest of the insulation.
Turn the base on the side and mark a spot 1/2 inch from the edge on the side of the board. Using the hammer, nail a blued tack part of the way in at this spot. The blued tack looks like a small nail. DO NOT bang it all of the way in yet. Turn to the other side of the board and do the same. Again DO NOT bang the blued tack all of the way in yet.
Wrap one end of the bare wire three times around one of the tacks. Carefully pull the wire tightly across the board to the other side and wrap it around the other tack. It is extremely important that the wire lay flat against the surface of the board. Now pound the blued tacks the rest of the way in. This should secure the wire into place. Leave the excess wire hanging off the second tack for now. See the sample photograph if you have questions.
First mark the location for the nail in each of the 9 brass strips. This will be in the middle of the strip 1/4 inch from the end. Position the strips evenly along the length of the base. There should be about 3/4 inch between the centers of each strip.
Use a hammer and the large nail to make a small dent in the strip and wood at the proper location on the base. Do not pound the large nail all of the way in, just use it to pierce the brass strip and then remove the large nail. The dent made in the brass strip and the wood will make it easier to put the blued tack through the strip.
Install the keys by pounding blued tacks into the brass strips. DO NOT
PUT THE TACK IN ALL THE WAY. LEAVE PART STICKING UP FOR LATER USE. This
is easier to do if you use a pair of pliers to hold the tack while you
attempt to pound it in. Leave about 1/8 to 1/4 of the tack exposed. Later
wires will be wrapped around the tacks. The keys are now complete.
Find the aluminum u-shaped battery holder. The holder itself will be used to mark the position of the mounting holes. Position the battery holder on the upper right side of the board, about 2 inches from the top and 1.5 inches from the side. Mark the spot of the two mounting holes. Remove the holder. Drill holes in the board at these two spots. Obtain two silver-colored screws and install the holder.
Connect the wires from the circuit board to the keys. Some of the wires may need to be trimmed for a neater appearance. Remove the insulation from the end of the wire. Form a hook on the end of the and place it around the tack or wrap the wire twice around the corresponding tack. Pound the tack the remainder of the way into the board. Repeat for each wire. It may be more convenient to wrap all of the wires first and then pound in all of the tacks.
If necessary bend the keys slightly so they do not touch the wire running across the bottom of the wooden base.
Trim the bare wire connecting all of the keys and solder this to the gray wire from the common of all keys on circuit board. If needed, use tacks to hold this into place neatly along the wooden base. Refer to the sample keyboard.
Install the three long screws (1 1/2 inches long) that will hold the speaker. Be careful not to extend the screws through the bottom of the board. Locate the speaker and use a rubber band to hold the speaker in place.
Part IV Tuning
Part V On/Off Switch
Part VI Final Check
© 2001 John J. Krupczak, Jr.
All rights reserved. Reproduction in whole or in part in any form or medium without express written permission of the author is prohibited.