QUESTIONS ANSWERS ■ WITH RUSSELL KINCAID &
In this column, Russ answers
questions about all aspects of
electronics, including computer
hardware, software, circuits,
electronic theory, troubleshooting,
and anything else of interest
to the hobbyist. Feel free to
participate with your questions,
comments, or suggestions. Send
all questions and comments to:
QI have a small vineyard; it’s a 400 ft run of various grapes for eating and wine. Birds are a big problem ...
they think they know when the
grapes are ripe. The grapes look
good and smell good, but the birds
will peck at each one trying to find
that sweet one. I’ve tried cyclic and
distress type scares, but to no avail.
Neighbors don’t like the birds, either.
I would like to try some ideas on
having an air poppet type noise
sound off when a varmint enters the
immediate area. I don’t know how
much of an IR footprint a bird has,
but motion sensors pick up on leaf
I would like to build a bunch of
small units, pot them against the
environment, and have them able to
drive a 24 VDC air solenoid (air and
DC voltage available along arbor).
I’m thinking one every 10 feet, or
closer to get the right IR ID. The
solenoid could be a triggered one-shot, or maybe in some ramp-up/ramp-down fashion. Any ideas?
— Rich Harrison
AHarbor Freight Tools sells an IR sensor that turns on a light at night when motion is sensed. I had one; I
removed the light and replaced it
with a solid-state relay. The daylight
sensor was covered with tape so it
worked all the time. A person could
stand in the view of the sensor and
not be detected, but any movement
would set it off. I don’t know how
24 June 2013
close a bird would have to be to get
sensed, but it’s worth a shot.
This sensor does not use the
Doppler effect; I think it senses
distortion of the IR field, so I wonder
if an object (like leaves) that is not
warmer than the surroundings would
QI am a long-time reader of your column and I’m hoping you can give me some advice. I’m working
on a battery-powered project. The
components have an absolute max
voltage of 5.5V and a minimum
operating threshold of around 3.6V.
In standby mode, the current drain is
around 200 µA and in active mode,
around 500 mA. Three C or D
alkaline cells would do the job, but
I’m trying to hold down operational
costs by using rechargeable batteries.
I would like to use NiMH cells
because of their good low
temperature operation and low self-discharge. Four cells would give me a
good range of operation, except that
when fully charged they would
exceed the max voltage allowed. Is
there some way to limit the full
charge voltage to a safe level without
hurting capacity too much?
I could use more cells and
regulate the voltage down to 5V or
so, but the regulator would have to
be very efficient to minimize standby
current drain and still provide at least
500 mA in active mode. I’m stumped
and I’d appreciate any suggestions.
— Richard Duncan
AIt seems to me that a switching power supply is what you need. I searched the Mouser catalog and
found one for $9.52. The load is not
isolated from the battery, but you
don’t need that. It is rated 15 watts,
so your application at 2. 5 watts will
be no sweat. Efficiency is said to be
90% (probably at full load and max
The input voltage range is 3V to
13. 8 VDC, and the output is
adjustable from .59V to 5.1V. The
supply draws 50 mA no load, but it
has an enable pin that will allow you
to shut it down where it draws 5 mA.
If your circuit is mostly in
standby, you may want to use a solid-state relay to disconnect the battery
during standby. The datasheet
doesn’t say, but the output
adjustment is probably a trimpot.
The Mouser part number is 826-
QI’m looking to build a simple detector circuit to test my electric fence. It can be a tone or a lamp,
but preferably an LED circuit that I
can hang on the fence permanently.
— Mike Phillips
AA neon lamp should work; the electric fence produces high voltage — just what he neon lamp requires.
You will need some series resistance,