■ WITH RUSSELL KINCAID
In this column, I answer 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:
Join us as we delve into the
basics of electronics as applied
to every day problems, like:
Fish Feeder ✓
● Ferrite Core Search
QI was curious about basic semiconductors like diodes, rectifiers, and transistors. I knew that a switching
transistor was an NPN junction and
that diodes are PN. I was wondering
if you could make an NPN transistor
out of two diodes (NP-PN)? This
should make a NPPN junction which
would be the same as NPN.
— A. Lingenfelter
AI am sure that what you really want to know is why that does not work. Here is why: The P region has to be
very narrow so electrons can transit
across it. Current from the emitter (N)
to the base (P) enables a greater
current from the emitter (N) to the
QWould you please tell me how to change a digital alarm clock from the xisting piezo electric
buzzer to a flashing 60 watt bulb?
We are very hard of hearing and our
existing KEN-TECH clock quit. It used
to flash a screw-in bulb. New clocks
we’ve seen don’t have an outlet for a
bulb. Thanks for any help you can give.
28 November 2009
— Frank Lemon
AOpening the clock and finding the switch that turns on the buzzer might be difficult, so I think the best
solution is a microphone sensor to
operate the bulb. A VOX kit from
Ramsey Electronics will do the job
but you will also need a power
supply, power socket, and relay. If you
have a 12 VDC, 200 mA wall wart in
your junk box, that will do, and you
may find the power socket and relay
at RadioShack. Otherwise, the parts
list below will work.
VOX kit $9.95 part no. VS1
Wall wart $13.89
418-TR1512-01-12 ( 2. 5 MM plug)
Power socket $0.87
16PJ221 ( 2. 5 MM)
QSeveral years ago, I read an article on how to use a silicone diode attached to an airplane engine cylinder
head for temperature measurements.
I can’t remember what publication I
read the article, or what year it was,
and Google doesn’t find any
Do you have any ideas on how
a standard diode could be used to
measure temperature while it is
physically attached to a cylinder
head? I always enjoyed the Q&A
section by TJ Byers, and you are
doing a fine job following his lead.
Please keep up the good work!
— Larry Kraemer
AA silicon diode has a temperature coefficient of about - 2 mV per degree C. For best accuracy, you
would measure the diode voltage at
several temperatures and draw a
curve or use a lookup table.
Another option is to use an
LM34 ( 10 mV per degree F) or LM35
( 10 mV per degree C) temperature
to voltage sensor. You can read the
temperature directly on a DVM.
The operating range is - 50 to +300
FISH FEEDER PROJECT
QI have to build an automatic fish feeder for my final project. I am using an 8051 microcontroller, seven
segment to display the time,
pushbutton to set the time, toggle
switch for on-off, and a DC motor.
I am now confused to build the
circuit and hope you can help me.
— Naim Romero