READER-TO-READER TECHFORUM
>>> QUESTIONS
Photoresister Switcher
I would like to know if I have
correctly connected the photoresistors
(CdS photocells) shown here in order
to turn OFF during the day and to
turn ON during the night the two LED
circuits attached to them. (If not,
please indicate by a new diagram.)
Also, I would like to know:
a) If any photoresistor would
work?
b) What would the optimum
dark/light resistance values be for such
a photoresistor?
c) How would I calculate the values (any formula?) from the transistor
side (2N2222) that would best fit this
ON/OFF photoresistor switcher?
#7141 Nate
via email
Wireless Mirrors
I have an old car that came with
electric windows but has old fashioned
side view mirrors which are almost
useless. I would like to upgrade to
more modern mirrors that are aimed
by control of 12V electric motors. On
the driver's side, that is no problem
as you simply use a four-way switch
scavenged off the vehicle that you
got the mirrors from, using the 12V
available to run the electric windows.
However, to use that same switch
to control the right hand mirror, I
would have to drill a hole in the edge
of both doors and both front pillars,
and snake a wire through from the left
side to the right side. It occurred to me
that the use of radio waves from the
left hand door could be used to
control four relays in the right hand
door and obtain the required action.
Something like Ron Newton used
in his “Super Detector” article in
the October 2013 issue of NV. Any
suggestions would be appreciated.
#7142 Dean Kaul
Kalamazoo, MI
Lithium Charging
I'm thinking of building a solar
charger for my iPhone, but don't know
how to handle the internal lithium
battery in terms of taper current, etc.
— especially when I have the phone
on all day. What I've found online is
information on charging disconnected
lithium batteries, not ones under load.
Any hints?
#7143 Anthony Suchek
White Plains, NY
#4144 - April 2014]
Receiver ... Not
I inherited an old tube-type short
wave receiver from my grandfather. It
produces nothing but static, even after
I replaced all of the vacuum tubes. All
of the switches are good.
#1 Nearly any serious restorer of
antique electronics — especially old
radios — will first replace all
electrolytic and paper dielectric
capacitors in the receiver. This is
especially true if the radio has been in
storage for a long time. Electrolytics
dry out and power supply filtering and
decoupling become poor. Paper
dielectric caps get leaky over time —
but paper only. Don't worry about
ceramic and mica caps at this point,
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>>> ANSWERS
78 July 2014