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15.6 Parts placement diagram for PC interface

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100K-ohm resistors (color bands brown, black, yellow, gold, or sil-
ver) labeled R1 through R10. Next mount the fives diodes D1 to D5,
making sure the black band on the diode faces toward the DB25
connector, as shown on the white line component drawing. Next
mount 15K-ohm resistors (color bands brown, green, orange, gold,
or silver) R11 and R13. Mount the red light-emitting diode (LED) in
the R12 position on the board. The positive lead of the LED is
mounted in the label R12 hole. Next mount the 14- and 20-pin
sockets in the U1 and U2 positions. Mount and solder the DB25 right
angle connector. Do not force the DB25 pins through the board; it is
a precision fit. If necessary, gently rock the connector in, making
sure not to bend any pins. Mount the slide switch and the 7805 volt-
age regulator. Cut and solder four wires above the switch. Take care
to keep the wire orientation as shown. Mount and solder the TIP 120
and TIP 125 transistors. Finish the project by mounting the eight-
position header and 3" connection cable. The header is mounted so
the longer leads face upward. Insert the two ICs, the 74LS373 and
74LS164, into their respective IC sockets. Be sure to orient the chip
indentation on the top side of the chip with the indentation on the
white line drawing. You may notice that there are places for addi-
tional components. This is for an additional AC adapter. Figure 15.7
shows the top side of the finished interface.
Team LRN
Robotic arm and IBM PC interface and speech control