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All of the button selections are handled using ten control lines in a matrix. A matrix is similar to the rows and
columns of a table. The matrix is as follows:

On power-up, the rhythm is stopped, rhythm selection is set to Pop, timbre selection is set to Piano, Tempo is
set to medium, and Vibrato is OFF.

Percussion (drum-like) sounds are created by playing a short pattern stored in the IC 9037’s electronic memory.
All four percussion sounds may be played at the same time. If the demo or one of the rhythms is selected then
a much longer pattern is played from the part’s memory in a similar manner. This will include both the tone and
percussion circuitry just described and will be repeated until the user presses the stop button. The tempo is
adjusted by changing the rate at which this tone pattern is played from memory (by dividing the 523.252 kHz
timing reference differently). The vibrato effect is created by varying the divide ratio to the tone circuitry slightly,
which will vary the tone frequency and hence the pitch of the sound.

The outputs from the two tone circuits and the percussion circuits are combined. The two volume control
switches adjust the strength of the tone and percussion signals before combination; weaker electrical signals
will resulting in weaker sound waves from the speaker. The combined result is smoothed (to remove unwanted
higher frequency signals that were created along with the desired tone and percussion signals), increased in
strength (amplified), and applied to the speaker where it is converted from electrical waves to sound waves.

If you are unfamiliar with

printed circuit boards (PC boards) then observe the advantages that the AK-900 board

provides. Notice all of the long, thin copper traces on the board; these are equivalent to having wires connecting
all of those points but is much easier to manufacture, much smaller, more reliable, easier to inspect for mistakes,
looks nicer, and costs much less. This board has only a single layer of copper traces; circuit board technology
has progressed to where boards with 6 layers of traces are not unusual. The board also provides stable
mounting for all of the other components.

Solder is used to connect the copper traces to the components

mounted on the board; it is metal that melts at temperatures typically between 400

F and 800

F. Electronics

manufacturers have refined their soldering processes into a fine art through the years. Observe that IC 9037 is
the only component in the AK-900 mounted directly on the printed circuit side of the board with no holes through
the board; this is called surface-mounting and today many electronics products have ALL of their components
surface-mounted due to its advantages in saving space (this was not a concern on the AK-900 due to the space
required for the keys and buttons).

Column 0

Column 1

Column 2

Column 3

Column 4

pin 66

pin 67

pin 68

pin 1

pin 2

Row 0

Pop rhythm