Caple C871i Manual de usuario descargar pdf (Pagina 92)

100

101

Apple II Computer Info

The new circuit uses transistors to drive the LED sections. By

getting LED power from the +12V line switched by power transistor Q1 in

response to /Drive Enable, the transistor used for this purpose in the

old circuit is eliminated. So, the new circuit needs only two

transistors-- just one more than before-- and drives the Green/Red LED

at higher brightness.

As in the original design, the new circuit shows Green for Drive

Enabled + no Write and Red for Drive Enabled + Write. That is, a Read is

assumed if the drive is ON and no Write is occurring. The advantage of

this approach is that you always have a lighted LED 'drive ON' indicator

and, so, there is no need to drill a new hole in your drive panel. The

new LED can use the hole occupied by the old "in Use" indicator LED.

Parts

IC- 74121 or 74LS121 1-Shot multi-vibrator

Qgreen- 2N2222A gen purpose NPN transistor

Qred- 2N2222A gen purpose NPN transistor

Rcath- 120 Ohm 5% 1/4 watt resistor

Rgreen- 3.3k 5% 1/8 watt resistor

Rred- 3.3k 5% 1/8 watt resistor

Rp- 20k 5% 1/8 watt resistor

Cp- 10uF/10v 10% "dipped tantalum" capacitor

LED- 2.2V 20ma 3-lead (common cathode) Green/Red bi-color LED

Building the Circuit

IC- locate pin-1 and mark it on bottom side with white-out.

'Dead-bug' mount the IC using epoxy in the open area near

top-middle of board with pin-1 end pointing to the right.

connect Rcath to solder pad at - (minus) end of C2

connect #20 wire from IC pin-7 to solder pat at - end of C2

connect Rp from IC pin-11 to IC pin-14

connect Cp + to IC pin-10 and Cp - to IC pin-11

connect #20 wire from IC pin-14 to solder pat at + end of C4

connect a wire from IC pin-3 to end of R16 closest to 74LS125

connect Rgreen to IC pin-1 (74121 "/Q" output)

connect Rred to IC pin-6 (74121 "Q" output)

solder transistor Qred Collector to Q1 power transistor Collector

(solder pad area at left front of circuit board just to left of

the power transistor). Position toward left edge of pad.

solder transistor Qgreen Collector to Q1 power transistor Collector

solder pad to the right of Qred.

LED- connect a 3-wire 11" cable to the LED (black to center, red to

to lead with right-angle bend, green to lead with slant bend).

Old "in Use" LED- pop off the retainer ring and push through the

LED. Leave the LED mount in the hole. Cut off the LED, spread

cable ends and tab over with cellophane tape. (Put old LED and

Apple II Computer Technical Information : Apple II Family Hardware Info

ftp://ground.ecn.uiowa.edu/2/apple2/miscinfo/hardware : May 2001 : 92 of 572

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Caple C871i Manual de usuario Pagina 92

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Caple C871i Manual de usuario Pagina 92

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