Nuts and Volts - July 2014

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,

All questions AND answers are submitted by Nuts&Volts readers and are intended to promote the exchange of ideas and provide assistance for solving technical problems. All submissions are subject to editing and will be published on a space available basis if deemed suitable by the publisher. Answers are submitted by readers and NO GUARANTEES WHATSOEVER are made by the publisher. The implementation of any answer printed in this column may require varying degrees of technical experience and should only be attempted by qualified individuals. Always use common sense and good judgment!