1 - 3 ft
10k 100k 33k 8 4
Figure 3. The receiver is tuned to 300
kHz; the sensitivity is adjusted by the
length of the antenna in the range of
1 to 3 feet. The longer the antenna,
the more sensitive the receiver. The
receiver outputs a pulse to the 555
monostable timer when a lightning
strike is detected, which causes the
piezo buzzer to beep.
A 5 volt Pulse Out signal is also
available to start a timer, which you
can stop manually when you hear
the thunder (or build your own sonic
thunder detector). That will give you
the distance to the strike. To triangulate, you’ll need two or more
receivers and a software program
(like Excel) to do the math.
more often than not, I forget to shut
off the light. Since the shed has no
windows, I never notice that the light
is on until my next trip to the shed.
What I’d like is a timer that would
automatically turn the light off after,
let’s say, 15 minutes.
The switch should work normally if you flip it off before the time
expires; otherwise, the timer would
take control and turn off the light.
Ideally, all the components would fit
in a standard electrical utility box,
along with the switch. An adjustable
time delay would be nice. Any ideas
on how I might build such a device?
shed and moving around, the light
remains on. Of course, it has its
drawbacks. If you working in an area
that has you shielded from the
sensor, you could find yourself in the
dark. So, I can see why you might
want to build your own timer circuit
with a predictable off time. For this, a
single 555 IC and an optoisolator
(Figure 4) will do the trick and the
circuit will easily fit into the utility box.
This circuit requires that you
remove the wall switch from the AC
wiring and use it to switch the 9 volt
power source instead. This can be a
9 volt battery, but I’d use a wall-wart
because the circuit won’t work if the
battery goes dead. Turning “on” the
light applies voltage to the 555 chip.
The 0.1 µF cap on pin 2 forces the
trigger input low during power-up
and starts the timing period.
The time is adjustable between 2
and 20 minutes using the 1M pot. If
you turn off power to the chip before
the time expires, the optoisolator’s
LED goes out and the light turns off.
If you forget and leave the switch on,
the 555 timer will turn off the
optoisolator LED and do the job for
you. When building the circuit, be
sure to keep the AC mains as far
away as possible from the wall switch
and 555 circuitry.
Q. When I want something from
my shed, I flip on the light, get
what I need, and leave. Of course,
A. My first suggestion is to install
a motion detector wall switch,
like the one made by Eagle that’s
available at most hardware stores
($19.95). As long as you are in the
Low Voltage 555
Q. I’d like a 555 timer to actuate a
relay ( 5 VDC @ 150 mA) for 1
NUTS & VOLTS
Wall Switch Timer
1 6 180
160k 8 4