AThe 8051 is a 40-pin DIP with four 8-bit
ports; you will have
plenty of outputs
for your project. The
circuit is no problem,
the program is what
will take time and
study; I can’t help
you with that. You
only want to feed
the fish once per
day and the fish
don’t care what time
it is, so I don’t see
the need for a display.
However, if it is part
of the project, you
could use a 7447
BCD to seven
driver or code the
driver in software.
could advance the time in hour
increments until you get to the desired
time to start the feeder. You will need
two digits for a 24 hour display. How
you drive the motor will depend on
the means of delivering the food. I
would expect the motor to only turn
once to dump a load, so a cam and
microswitch could signal that the motor
should stop. A gear reduction motor
that turns very slowly is indicated.
A possible circuit diagram is
Figure 1. I show two 7447s assuming
you will code the two seven
segments separately rather than
multiplex them because there are
plenty of ports. I show inputs to port
0 because my limited perusal of the
datasheet indicates that port 0 can
■ FIGURE 1
Re: Antenna Question, September,
‘09, page 30. The answer given to the
question about “passive” AM antenna
(boosters) kind-of strayed from the mark!
What the originator was doubtless
referring to was the large coil/tuning
capacitor in a box that you place next to
an AM table or portable radio.
This is simply a re-radiating,
resonant, L/C circuit where the large coil
can intercept more signal off the air than
be an input. Q1 is a 100V, 10A logic
level MOSFET (overkill but cheap).
Your program will have to acknowledge that S3 (the microswitch) is
closed and wait for it to open and
close. There is an Intel forum that
may be helpful, and the 8051 code
set can be found here: www.atmel.
Good luck on your project.
FERRITE CORE SEARCH
QI am looking for Philips ferrite core, part number RM8RA250-3B9. Could you please help me find a
a small radio’s internal loopstick.
Inductive coupling sends this larger
signal into the radio. Tuning the capacitor
in the booster peaks the desired station’s
signal. The comments about a “quarter
wave dipole” (non-existent) made me
grin. The answers about digi and high
tech stuff are usually right on point, but
antenna and RF basics???
— John W. Davidson
Certified Wireless Technician
ETA International CET
Amateur Extra Class Ham
source to get that core or a
— S. Karas
APhilips ferrite operations were bought by Yageo which also owns Ferroxcube, so I queried
Juan Carlos Gardea of Ferroxcube.
He says the RM8R number is not
good and 3B9 material is obsolete.
Juan suggests that RM8/I-3H3-A250
or RM6R-3H3-A250 would be
equivalent. Apparently, 250 is the
Al in nH per turn and 3H3 is the
material which is low loss and good
for filter applications below 2 MHz.
Unfortunately, there is no distributor
for small quantities but you may be
Response: Thanks for writing. I admit
my answer did not answer the question;
I had never run across such a thing as
a passive signal booster and doubted
that it would work. After reading your
message, I built one to try it. I wound 20
turns #24 insulated hookup wire on an
oatmeal box (five inches diameter). The
tuning capacitor was a variable, 65 to 650
pF. I put the coil (horizontal) next to my
portable radio and tuned in a weak
station near 1400 kHz. Surprise! It works!
I got a noticeable increase in signal by
tuning the variable capacitor.
November 2009 29