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General
The Control Panel PCB connects to the Interface PCB via a single 26 wire at cable. This carries
row and column signals to the switches and LEDs. It also carries the three volume control
signals and headphone audio signals.
LED Matrix
The 12 individual LEDs and 70 display module LEDs are combined together into a single 12
column by 7 row matrix. The 12 columns are named C0––C11 and the 7 rows are named LR0––
LR6. An LED will turn on if the column it is connected to is a low voltage (less than +1.0V) and
the row it is connected to is a high voltage (more than +2.5V). The columns are driven to a low
voltage one at a time while the rows are driven high in various patterns to create the desired
light pattern.
Switch Matrix
The 12 individual switches are connected to a 6 column by 2 row matrix. The columns are
shared with the LEDs, but the 6 rows are separate. A pressed button switch will pull its row to
a low voltage (less than +1.5V) when its column is driven to a low voltage.
Volume Control
The three volume control signals simply connect to a single 10K potentiometer. The VOL W
voltage as a percentage of the VOL H voltage depends on the volume control position. Zero
percent (0V) is no volume and 100% (5.0V) is maximum volume. Because it is a DC control
voltage, small amounts of noise pickup will not be heard.
Headphones
One or two headphones may be plugged into the two jacks, J4 and J5. When headphones are
plugged in; resistors R2, R3, and the MUTE signal tell the Interface PCB to mute the speakers.
In practice, MUTE is at +5V and a small current, absorbed by the headphone amplier, ows
through the resistors. When one pair of phones is inserted, the current ow is reduced by 1/2.
This is detected by the Interface PCB and causes the Mute relay to close and silence the
speakers. When both headphones are inserted, the current is completely interrupted but still
operates the Mute relay.
Printed Circuit Boards
Control Panel PCB
2- 13
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