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Assistance Against Cyber Attack 2020 Issue-5

What materials make a good phased array antenna (i.e., efficient transmission and reception and the shape of the individual components)? What frequencies go through earth and seawater above 10 GHz also?

#05203
William Zimmerman
via email


In-Line speaker Amp 2020 Issue-5

I recently moved into a home that has in-ceiling speakers. I have them connected to an A/V receiver and in one room they work great. In the other room, the sound is very muted. There’s a volume control in that room which I’ve replaced and checked. I’m looking for some kind of amplifier that I can purchase or build that can just increase the volume level on that pair of speakers (there’s a pair leaving the receiver which goes into the volume control and then splits into four speakers). I have checked obvious issues and swapped the A/B pairs just to make sure my receiver hasn’t failed.

#05202
Michaeljon Miller
Trabuco Canyon, CA



Answers

Because you swapped the A/B speaker leads and got the same audio results, the culprit might be speaker-impedance mismatch. Check the output impedance of your A/V receiver and of the low-volume speakers. The receiver manual should specify an impedance, which in most cases comes to, 4, 8, or 16 ohms. If not in the manual, check for a label at the outputs. 

Also, find the impedance of your speakers in the manufacturer's information or on a speaker label.  You want the same impedance at both ends.  A mismatch can cause reduced volume and even distortion. If you want to measure impedance, here's a link to a helpful article: https://www.wikihow.com/Measure-Speaker-Impedance. If all else fails, look for an impedance-matching transformer. More information here: https://www.electronics-tutorials.ws/transformer/audio-transformer.html.

Jon Titus
Herriman, UT


Battery Woes 2020 Issue-4

I have some brand new lead-acid batteries that have never been used. They have been stored in my garage for a while (1-1/2 to 2 yrs). My smart charger errors and won’t charge them. Why is this and is there anything that can be done to revive them?

#04205
Reva Pino
Charlotte, NC


Capacitor P&Cs 2020 Issue-4

What are the pros and cons for using electrolytic capacitors in a voltage divider circuit to provide about 24 volts AC to a heater cable from the 120 volt AC line?

Is there a possibility of having a capacitor explode from overheating? If so, could that be prevented by stringing several capacitors in parallel to provide for additional heat dissipation?

#04204
Robert Gotts
Madison, IN


Temperature Sensing LEDs 2020 Issue-4

I’m looking for a temperature sensing circuit that will light each of three LEDs at approximately 80°F, 90°F, and 100°F.

#04203
Matthew Seltzer
via Internet


Fan Indicator 2020 Issue-4

Good day to all you experts!  I have a plywood basement floor that is suspended like any other floor in the house (bentonite soil in my area requires this construction). The actual dirt ground is about two feet below the wood floor, covered by a rubber tarp.

To prevent a build-up of mold and stale air, this space has a 6” duct vent fan that turns on via a humidity sensor rheostat. The supply side duct is on one side of my basement and the evacuation duct is on the other.

In the past, I could hear this fan running, so I knew when the bearings were wearing out. It was an easy job to buy a new duct fan and replace it. We just had our basement finished, putting drywall around the perimeter wall. Now I can no longer hear this fan when it kicks on.

Does anybody have a suggestion for some sort of sensor that detects when the fan is turned on by the humidity sensor but drawing too large of a current supply, so on the verge of bearing failure? Ideally, I would like some sort of an indicator light that I can make part of the access panel that is over the fan. Even an AC ammeter movement would be adequate.

At the location of the fan, I have both the switched 120 VAC power supply and a constant 120 VAC available if needed. I don’t have the specifications on this exact fan available, but a quick search online found several that had operating currents of 0.35-0.40 amps. I know the start-up amps would be a little higher but not too much because the motor is small and has very little inertia to overcome. Thank you for any suggestions!

#04202
Bill Young
Denver, CO


Component Footprints 2020 Issue-4

Can someone please explain the standards for the footprint of electronic components? I’m trying to figure out the the best way to lay things out on a circuit board. I’m new at this and any advice would be appreciated.

#04201
James Devera
Scandinavia, WI


Bench Power Supply 2020 Issue-5

I would like to build an inexpensive AC power supply for my workbench. I want something much smaller and lighter than a variac, 0-30 VAC, and maybe one or two amps would be fine. Can anyone point to a good schematic or even a well-written circuit description?

#05201
Jeff Bowles
Columbus, OH


Electronic Candle Circuit 2020 Issue-3

I’m looking for a simple circuit for a 24 hour electronic candle that uses very little power. The candle would drive a single LED. It would run for x hours (say five), then turn off; 24 hours after it  has first activated, it would automatically turn back on for the predefined time.

I've found several ideas, but most of them surrounded the 555 chip which has a very limited time frame.

#03205
Scott Lapp
Simi Valley, CA



Answers

It would be almost trivial to write a small program for a microcontroller to do this. I actually built almost the same thing to turn on a window fan in the evening and off in the morning. An 8 pin PIC with a 32. 768 Khz crystal. A single button reset the processor, which then would time for 24 hours, then activate the fan. Easy enough to add additional times. No display or time setting needed.

Richard Cox
Thousand Oaks, CA

Check out the Custom Silicon Solutions CSS555C Micropower Timer. With a little programming and perhaps a small additional capacitor you will be able to get the delay times your looking for. Also see the article https://www.nutsvolts.com/magazine/article/february2016_CSS555TimerICs

Kurt Stefans
Valparaiso, IN

I built a similar circuit to control a window fan. I wanted it to turn on and off at a certain time each day. I used an 8 pin PIC clocked by a 32.768 KHz crystal. The circuit was installed in the fan's remote controller.

Timer 1 was clocked such that it created a rollover interrupt every second. The software then counted the seconds and incremented a minutes and hour counter. Pressing a button connected to the reset pin set all the counters to zero. Then when the seconds, minutes and hours counters were zero every 24 hours it output a signal to the remote control button to turn the fan on or off.

What you want would turn the candle on when the hours and minutes are zero, then turn it off when the hours are five and the minutes are zero. Contact me at [email protected] for details.

Richard Cox
Thousand Oaks, CA


Home Circuit Boards 2020 Issue-3

Does anyone still make oneoff circuit boards at home? What methods are being used by hobbyists and where do you get supplies?

#03204
Alvaro Collazo
Gulfport, MS

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