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Recent Questions

2022 Issue-1


Arduino Clone - Yes Or No?

My daughter is preparing for a science fair. Each participant is limited to a total of $50 for parts and supplies. Central to her project is an Arduino Uno. I’m tempted to order a half-priced Chinese clone from eBay vs. an authentic model from one of the domestic supply houses. Is there a downside to using one of these inexpensive clones or are they identical to the real thing?

#01221
Diogo Alves
Saint Charles, MO


Adding Aux Input To Stereo

My car stereo boasts an AM/FM radio and a cassette player (2007 model. My smartphone, however, has all my stored music, Pandora, Amazon music, and even Satellite radio. There is no auxilliary jack or Bluetooth to connect my phone to the car stereo like with new units.

Is there a way to tap into the cassette deck circuitry and add an aux jack to use my phone as an audio source? Would I need a preamp or other circuit to create an interface or just a direct connection at some point inside the stereo?

#12222
Gilberto Onio
Framingham, MA


Logging Power Data

We have a Smart Meter installed for our home electric utility billing. Is there a way to read data from it to log usage data to a computer? I want to analyze my power usage by day of the week, time of day, devices and appliances in use, etc. Does the meter itself keep a log of this info that can be read or would I have to have a spreadsheet or other program to track it?

I'm not looking to interface any hardware to it. It would appear to have an RF link with the power company that might allow access. Any information about these meters would be helpful.

#01223
Lisa Miller
Cleburne, TX


2020 Issue-6


VSWR Value Change

Last night I was testing my 145MHz Yagi antenna for VSWR value when I realized something. When I kept the antenna close to ground, the VSWR value would change. Also, when I stood in front of the antenna the same thing happened.

I searched about it on the internet but I'm not satisfied. If any one knows the reason for this, could you explain it to me please. It will be really appreciated.

#06202
Emre Eroglu
KONYA


Sump Pump Monitor

My basement is prone to seepage. When the sump pump runs so often that there is only a 15 second off-time the seepage is eminent. I am looking for a stand-alone circuit that gives a digital read-out of the off time in seconds. An adjustable alarm output would be a big plus.

I am not concerned with sensing the pump power status, that I think I can do. The off time range of interest would fall between 120 and 2 seconds. I am sure this can be easily accomplished with an Arduino or Raspberry Pi circuit but I have no experience with either. Thank you.

#06201
Allen Goodcase
Brookfield, IL


2020 Issue-5


Bench Power Supply

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


In-Line speaker Amp

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

It sounds like your problem is an impedance mismatch in the speaker system. Maximum power transfer occurs when the source impedance (output of your amplifier) matches the load impedance (speaker). The gauge of the speaker cable may contribute to the problem. The smaller the gauge the higher the IR loss in the wire. And NO... Monster Cable is NOT significantly better and definitely NOT worth the extra cost.

A better solution is an additional amplifier for those ‘other room’ speakers... defining another ZONE. That amplifier should be fed by a low level output from your receiver My guess is that the previous homeowner had a system with an amplifier per zone and a low level signal distribution system to feed the amplifiers. This can get a bit complicated in design but may translate into a more versatile system.

Douglas Hall, CPBE
Vilas, NC

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


Assistance Against Cyber Attack

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


2020 Issue-4


Component Footprints

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


Fan Indicator

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



Answers

As a first thought a current sensor, watching the motor’s current draw, comes to mind. A current sensor is simply a single winding coil that one motor wire passes through. It is a basic transformer and the coil develops a voltage relative to the motor current. They are available commercially or can be salvaged from a junk box transformer.

OK, but that seems to be more bother than it’s worth since all you really need to know is if the fan is running not it’s actual current draw. So now it looks like an air flow switch is the best choice. Don’t go off the deep end here, they are quite simple. Many commercial airflow switches are nothing more than a lightweight paddle connected to a micro switch actuator arm. This is placed in the airflow, the air lifts the paddle and the switch operates. Just be sure the paddle falls freely without airflow and that the airflow raises the paddle high enough that it doesn’t dance or flutter on the air stream.

A common SPDT micro switch offers many options for alarm or indication connections without the fussiness of measuring the current sensor voltage and the circuitry required. Since the micro switch is isolated it could be connected to a line power, low voltage or even an alarm system! Low cost possibilities and reliable operation are unlimited.

No power, clogged duct work or fan assembly, bound up motor, a squirrel in the squirrel cage... all result in no airflow! Not having specific information about your fan or it’s installation, it would seem easy to cobble this together with common, and easy to find items. Hope this solves your problem.

Len Powell
Finksburg, MD

Judging by the current, the fan motor is probably a shaded pole motor. Bad bearings may not alter the current very much, until they freeze up, at which point, you'd have the motor's locked rotor current. I assume you'd like to know about motor trouble before it fails. Since you are able to tell by ear, why not use a cheap intercom to monitor the fan?

Jonathan Wexler
Los Angeles, CA


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