ed by a Skeeball, the output goes low for
as long as the ball falls through the slot,
then returns to high. If your logic wants
the sensor to be low then go high, use
the (b) version of Figure 3. I’ve never
tested these resistor values with the All
Electronics parts recommended, so you
may have to tweak the 10K resistors up
(no higher than 100K) to get a positive
response. If a brighter light source is
needed, the 2.2K resistor can be
reduced down to 1K with no ill effects.
THE IN-N-OUT SENSOR
QI have a motion light for the
bathroom that is set for two
minutes. I would like to
replace it with an infrared
sensor that would come on when I walk
in and off when I go out.
— Clarence Hawkins
AAn IR heat sensor won’t work
as you plan because it will
give false readings from a lingering shower, space heater,
and other heat sources that remain after
you’ve left the bathroom. How about an
ingress/egress detector that would monitor your direction into or out of the room
and control the light accordingly? All it
takes is a pair of photosensors steering
+12V
Sensitivity
100K
100K
1K 1K
4011
0.1
Q1
4011
4011
a logic circuit, as shown in Figure 4.
The circuit works by determining
which photosensor is activated first.
Let’s say the light source to Q1 is interrupted first. This causes the monostable
timer (4001 gates) to start and lock the
states of Q1 (HIGH) and Q2 (LOW) into
the 4027 flip-flop. This causes the Q
output of the flip-flop to go high and
pull in the relay. It also locks out the
sensors for one minute so that further
movement will be ignored. When you
exit, Q2 is blocked and the Q output
goes low, causing the relay to drop out.
Placement of the sensors is critical.
Obviously, they have to be placed horizontally, one in front of the other. And
they have to be spaced far enough apart
so that both aren’t darkened at the same
time, yet close enough to be illuminated
from a convenient light source — which
can include IR LEDs, a night light, or
ambient room light. The sensitivity pots
adjust the trip point of the sensors.
Cadmium sulfide photocells can be used
in place of phototransistors Q1 and Q2.
COMPUTER PROBLEM
QI was trying to Network
Neighborhood my two computers to share my Panasonic printer from one computer
■ FIGURE 4
100K
4001
10uF
+
4001
to the other. I started with My Computer and went to — Printers, Panasonic
Printer, Properties, and to Details. Where
it asked “To Print To The Following Port,
I mistakenly entered Panasonic instead
of LPT1. Now when I try to click onto the
Panasonic printer I get an Illegal
Operation — with an explanation
SPOOL 32 caused a stack fault in module KERNEL 3.2.DLL at 016f:bff7a2al.
I tried to delete the Panasonic
icon, but it won’t let me. To get out of
this situation, I had to End Printers
Task and shut down the computer.
When I restart the computer everything works okay as long as I stay
away from the Panasonic icon. Even
highlighting the icon puts the system
into an illegal program situation. Is
there a way to rectify this problem?
— Scott Jones
ANormally I don’t answer
questions that deal with
specific operating system
software errors, but this is
one I ran across myself recently and can
answer without reserve. The problem
is in the Windows XP Registry. You have
cross-linked the two devices (port and
printer) and XP is confused, which is
why you are getting the error message.
You need a good Registry software
program to set things straight.
I personally use Registry Mechanic from PC Tools ( www.pctools.com),
which sells for $29.99, but a search of
the web will turn up both freeware and
shareware for less — most of which
I haven’t tested. I suggest that all
Windows XP users do an occasional
scan of their Registry — and each time
you make a change to your system. You
never know what secrets are lurking in
a new application.
T-BIRD TAIL LIGHTS
Q2
4011
4027
1N4001
Q1 and Q2 can be replaced
with CdS photoresistors.
_R
QK
CP
QJ
S
2N3904
12V
Relay
1K
In 'N' Out Direction Detector
QA friend who creates miniature dioramas of vintage automobiles recently asked me
if I had ever seen a circuit
that would simulate the turn signals
for a 1967 Ford Thunderbird. When triggered, the first LED would light, then
a second LED, and then a third. At this
point, the display goes dark and the
cycle repeats. He wants to activate
22
March 2006
