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Ethernet Port Expansion 2019 Issue-3

My Internet router is located near our entertainment center in the family room. There are only four Ethernet ports on the router and I have five pieces of equipment that need to plug in. I also run a cable from the router to my home office (in the back of the house) that connects to an Ethernet switch that provides Internet to multiple computers, VOIP phones, as well as network connections for various printers.

At the router, I have to plug and unplug whatever equipment I want to use, since I don’t have enough ports to keep it all plugged in. Some devices can use the Wi-Fi, but performance is better and more reliable on the wired connections.

Questions:

  1. Can I add another switch at the router to expand the number of ports?
  2. What are the limitations/drawbacks on adding more switches to the network? (I currently have two in the office.)
  3. Is there a better way to do this?

#03193
Byron Rochefort
Fort Wayne, IN


Image Reverse 2019 Issue-3

I’m building a rear facing camera system for my car that displays the image on a 7” screen mounted on the dash. However, the image appears reversed horizontally. Is there a circuit to flip the image left to right so it would be correct from the perspective of the driver? Any ideas are appreciated.

#03192
Krystian Czarnecki
Lombard, IL



Answers

Your best bet is to buy a backup camera that reverses the image for you. Many models let you select which way you want the image displayed. Depending on the resolution and night vision features you want, the backup camera can be purchased for under $20 online.

Bruce

You don't need any electronics. Instead of having the camera face backwards out your rear mirror, place it so it "looks" left or right. Then use a mirror at 45 degrees to the camera's optical axis (top view) and you'll get a left-to-right reversal of what your display shows. You could mount the camera and mirror on a plastic or plywood base and support the mirror with a small angle bracket that lets you adjust the angle so it suits your purpose. And you can move the base as necessary.

Jon Titus
Herriman, UT


Coil Winding Tips Answered 2019 Issue-1

I’m looking for some pointers on winding coils. On a second layer of winding, should the direction reverse when reaching the end of the core, or return to the starting side and wind in the same direction? It seems like winding in the reverse direction would cancel out the field. Does it matter which direction?

#1194
Jordan Bracegirdle
Toronto, CN



Answers

Assuming that the coil is being wound on a bobbin or other form, the coil is wound beginning at one end, laying down the wire turn by turn until the opposite end of the bobbin is reached.  At this point, winding continues in the same direction, but proceeding turn by turn back to the point of beginning, and so on. For an inductor, it doesn't matter which way you wind the turns so long as you're consistent throughout.

Others have raised this question; see, for example, https://electronics.stackexchange.com/questions/369884/how-to-wind-an-inductor.

A good document on building inductors was found on the ARRL site:

http://www.arrl.org/files/file/Technology/tis/info/pdf/9708033.pdf.

Good luck.

Peter A. Goodwin
Rockport, MA

It's the direction the current flow rotates around the former that matters. This does not change when your winding goes back along the core.

Kit Wareham-Norfolk
Exmouth, Western Australia

It is OK to wind a bobin from one side to the other and back. That is the way it is normally done. If you were to go back to the same side every time, you would end up with a nasty bump in the coil layers where the wire returns. And no, that does not cancel the flux field. Looking from the end of the coil, the windings are still in the same direction, either clockwise, or counter clockwise. If you were to change direction, say part of the coil is clockwise, and you now reverse that direction to counter clockwise on the next part, than those windings would cancel out the same number of earlier windings (in an idealized scenario). Those windings would become a simple resistor from an electrical perspective.

Bill van Dijk
Carp, CANADA


Troubleshooting Circuit Needed 2019 Issue-2

I’m looking for a circuit using a piezo buzzer, that I can hear from the room above the cellar. It will be connected to a Taco Heating Zone Valve on the boiler in the cellar for troubleshooting the thermostat when it goes on and off.

#3194
G Forcino
via email


SCSI Card Or Adapter Needed 2019 Issue-1

I have a bunch of old optical disks that have data archived from about 20 years ago that I would like to access. I found the stand-alone drive in a box of old computer junk, complete with the big SCSI cable. Problem is that I don’t have the computer anymore that has the SCSI card to plug it into, and don’t even know where to begin to look for one.

Is there something comparable that will work with a modern computer? An SCSI to USB adapter maybe? What about drivers? The old machine was probably Windows 98.

#1192
Mark Cisneros
Columbia, TN



Answers

I have a Win98 computer set up to read SCSI disc drives. It was a bear to create and find drivers for. I’m in Phoenix Arizona.

My next question is what software would be needed to read the data, is it just text? My setup was crated to be able to read and copy SCSI to sim cards, because of the lack of production of SCSI drives. I can currently copy from SCSI to sim cards if that would help. SCSI is old technology that is not really supported. If the data is important, I could probably read your drives and forward the data back in a usable format.

Let me know.

Antoinette Sides
via email

Adaptec made a USB 1.1 and a USB 2.0 SCSI to USB adapters; USB 1.1 M/N FX0C21902KL P/N 1861400; USB 2.0 M/N FX0A229005U P/N 1989100. I have one of each and they worked on every device I tried them on. Obviously the USB 2.0 is faster. I think the main drivers were Windows 98, but I can't recall for sure. I think I used them last under Windows XP.

Alexander Fisher
Galloway, OH

There are still PCI cards available for your SCSI drive, although they go by either GPIB or IEEE488 interface. National Instrument has both the cards and drivers (http://www.ni.com/en-us/shop/select/gpib-instrument-control-device). It would be difficult to connect the SCSI drive to the computer with a USB connection since the drive requires several control lines for proper access.

Lance Corey
Santa Ana, CA

I find some SCSI/USB adapters on eBay for around $170 to $300 each. I also find brand new SCSI/PCIe host adapters on Amazon for under $100. Either way, unless your cable is a Macintosh style cable (DB/25 to AMP50), you’ll also need a new cable. (For most of the PCIe host adapters, you’ll still need a new cable). What make and model are the optical disks? You may be better suited to pick up a used MO drive that’s SATA and use it on your current PC. Or with a SATA/USB adapter externally.

Ralph Phillips
Bossier City, LA


Ringing Of The Bells Answered 2019 Issue-1

Is it possible to replicate tubular bell tones with a microcontroller? I’m needing realistic, deep, resonating tones. If so, are there any micro requirements that would make one device more suited over others and how do I create the tones? I want to program short 10-15 sec jingles of my own composition.

#1193
Sara Hanchett
Forest Grove, OR



Answers

For the best result I would look at a MIDI solution with a sampled sound file.

Bill van Dijk
Carp, CANADA


Devices/Software/Scheme For Wi-Fi Remote Control Using Smartphone 2019 Issue-2

There are a number of articles in the past issues of Nuts & Volts for a variety of ways to control devices in a home using a variety of control devices and schemes. However, none seem to have the combination of characteristics that I want. I would like to control a pair of simple low current AC sockets (ON/OFF) from my cell phone. I would like to use a combination of an existing app, a PIC style device (Ardunio or whatever), and a Wi-Fi module to connect it to my existing Wi-Fi. I do not see why a $100 hub should be needed. My present cell phone uses the Windows operating system, but I know that apps for it are scarce and I am willing to get an Android device. I’m stuck on finding the cell phone app and the Wi-Fi module. I would assume that I would have to write the appropriate code for the PIC device. I can interface the PIC with a relay, probably a solid state one. Any suggestions?

#3193
Edward Alciatore
Beaumont


DC To AC 2019 Issue-1

I have a 100 amp 110 volt DC generator. I want to convert the output to 60-cycle AC. Does anyone have a schematic or info to build a converter? How much power loss can I expect in the final converted output? Thanks for any info.

#1191
Lucio Saunders
Indianapolis, IN



Answers

You don’t need a converter. You need an inverter. A converter is used to change AC into DC or DC of another voltage, while an inverter changes DC to AC. That being said, there are many ways to skin this cat, depending on how much you want to spend and what you want to use the AC output for. Before we go there though, we have to start with basics: the generator.

In your question, you did not specify the type of DC generator that you have or how you are driving it. There are three types: the shunt; the series; and the compound. Each has its own set of operating characteristics. I assumed that yours is of the shunt type, the most common. The Rheostat (R) is used to adjust the output. The voltage (E) and current (I) are monitored and the output is supplied through a 125 amp fuse.

Your generator is rated for 100 amps at 110 volts which is 11,000 watts (11,000/750 = 14.67 horsepower). Add 20% because no generator is 100% efficient, so about 18 horsepower is required to drive it at its rated speed. This is important because the output of a DC generator is related to both its field strength and operating speed.

There are three ways to do what you want to do.

The first option is the simplest — just use a 110 volt DC to AC inverter. These are around because they were once used on small hydro electric systems. You may be able to find one on the Internet, but I don’t recall any being large enough to handle 11,000 watts.

The second option is a bit more radical, but much more feasible as the inverters are widely available for usage in the alternative energy field. A pair of 48 volt magnum energy MS4448PAE inverters are connected in series and these are in parallel with a pair of series connected high-value capacitors. An equalizer line runs from the junction of the capacitors to the junction of the inverters. This works because these inverters like to operate around 55 volts and because their outputs are in parallel, they share the load evenly. The equalizer line is a safety to handle any imbalance.

As for output, these inverters are rated for 4,400 watts continuously, 4,800 watts for 30 minutes, and 6,000 watts for 30 seconds. The first two specifications are all that matter in your application. Assuming 90% inverter efficiency, the generator will supply 9,680 watts (88 amps) to produce 8,800 watts of AC. The generator will supply 10,560 watts (96 amps) to produce 9,600 watts of AC for 30 minutes at a time.

The third option is the most radical, but it allows two things the other options do not: redundancy and the ability to supply AC to the utility grid. This option utilizes microcontrollers commonly used on photovoltaic modules to convert low voltage DC into 60 Hz and then to synchronize this to the utility grid. I have chosen the Enphase Energy 250 watt unit. You will need 36 of them and they are used in groups of three to allow an input of 48 to 144 volts. This is well within the range of your generator.

The outputs of all the units can be connected together to produce about 9,000 watts of AC power at 120/240 volts or they may be connected for three-phase output at 208/120 volts. They must be connected to the AC grid to operate though. By having 36 units in 12 series strings, the failure of a single unit will only reduce the output by a little more than 8%. It was nice talking about the good ole days of DC. If you have any other questions, you can contact me directly at PO Box 9106, Concord, MA 01741.

Craig Shippee
Concord, MA


Side Lights As Turn Signals - MG Auto 2019 Issue-2

My brother has an old MG that he likes tinkering with. He wants to use the side lights to indicate when the turn signal is on for drivers that are on either side of him. Normally, the side lights turn on and off with the headlights.

In his case — and to reduce peak power consumption to the blinker circuit — he would like the side lights to turn on when the signals are off, and vice versa (when the turn signal switch is turned on). Additionally, if the lights are on, the side lights should give priority to the turn signal, turning on and off, opposite to the signals in the front and rear, and returning to full on when the turn signal is not engaged.

I think the simplest way to do this would be with solid-state relays and the use of some logic gates (for each side). I have built hundreds of logic circuits, but have not really dabbled much in automotive applications. I know the electronics have their own temperature and performance specs and are noisy environments, not to mention the notoriously bad reputation that English cars have for electrics. Can you recommend a circuit for this application? (This car is a NEGATIVE chassis).

#3192
Patrick Gilmore
Amherst


About Resistors November/December 2018

Could someone explain what pull-up and pull-down resistors are, when and how they’re used, and how to calculate their values?

#11187
Andy Dietrich
Dallas, TX

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