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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

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


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


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


Tuning The Music Answered November/December 2018

Is there a way to vary the speed of a music CD player? I play my instruments along with the recordings and need to vary the pitch slightly to match the tuning of my instrument. We used to do this easily with vinyl by varying the speed of the turntable.

#11188
Klaus Herman
Raleigh, NC



Answers

CD players for professional/DJ market have variable pitch built in.

Erik von Seggern
Escondido, CA

I would be surprised. CD players are designed to KEEP their speed. I would convert the song to one of the usual audio file formats (mp3, wav) and run it on a computer with the free audacity tool. That lets you change the speed and even allows you keep the pitch! (Effect -> Change Tempo; Effect -> Change Speed). I use audacity constantly.

Werner G
via email


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


Reflow Oven Opinions Needed Answered November/December 2018

Anybody doing SMT reflow soldering at home? Trying to make the switch from TH to SMT. I was wondering what homebrew oven setups people are using and any tips and advice for a newbie.

#11183
Joey Dampier
Reston, VA



Answers

A toaster oven can be used for reflow soldering work. I have one where one of the coils is broken, but the remaining coil gets it hot enough to melt the solder. I use an oven thermometer to monitor the temperature and approximately follow the recommended temperature/time profile.

Edward Alciatore
Beaumont, TX

I went down the path that you are, Joey. I was fortunate to have found SparkFun Electronics and even more fortunate that they had a kit with code ready to go. They’ve since discontinued that product, but there is a schematic and the code still on that site. I could simply regurgitate what is there, or not plagiarize by directing you there.

One thing that merits repeating is that you will need a toaster oven with at least 1500 watts (I used an Oster convection toaster oven) but 1800 watts would be better, especially if you’re going to use lead-free. That having been said, if I had this to do all over again, I’d not even use the timing aspect of this and simply experiment with how long it takes to melt the solder because it’is nearly impossible to replicate the Kester profile (that is published and out there if you look for it) with a toaster oven. Or, you can use a hot air gun (800-1000 degrees) to simply heat the board. It’s not as sexy, but it does the job just fine.

A word of caution on the toaster oven without using the timing function. DO NOT walk away, answer the phone, send a text, look out the window, chat with a friend... Do NOTHING except watch your work or you will have some very expensive, non-edible, toast.

Brendan Ames
Albuquerque, NM

It’s fairly easy and not expensive. People have successfully used toaster ovens, stoves, and kitchen hot plates. I use a $100 laboratory hot plate and monitor temperature with an infrared thermometer. The tricky part is laying down the paste for small SMT components. I strongly recommend an inexpensive stencil from oshstencils.com instead of doing it by hand.

Mike Hasselbeck
Albuquerque, NM

I worked for a while at a startup company where I (amongst other duties) built prototypes and very short runs, up to about 10 boards, that were nearly all surface mount technologies. If memory serves, at least one of the boards was about 8”x10” and had roughly 100 components on it, while others were a couple of inches on a side and only had a dozen or so components.

To build these boards, we would usually order a custom solder mask from Pololu (www.pololu.com) to use solder paste on the board. One word of caution is that solder paste has a relatively short shelf life, maybe 6 months, but that can be extended to at least 18 months if you keep it in the refrigerator. Take steps to make sure NOBODY tries to eat it!

Due to the nature of the solder paste, we wouldn’t start the process unless we knew we could finish it that day. We’d use the mask to put solder paste on just the spots we wanted. There are several techniques to hold the mask and board in alignment, then using good tweezers place all of the parts in their proper locations. Then we would “cook” them to “reflow” the solder.

Rather than using an oven, we used an electric griddle at that company. (DO NOT use the same one for cooking food later!) Once we had the boards ready to cook, we’d heat up the griddle using a non-contact infrared thermometer to check the temperature and for “hot spots.” We would use a flat metal spatula to transfer the boards onto the griddle, with something like a pair of tweezers or other small tool to slide the boards off the spatula and watch them closely to observe the solder becoming molten.

When all of the solder was molten, we’d wait another 5 to 10 seconds to make sure any hidden solder was also molten, then very carefully slide the boards back onto the spatula and transfer them to a heat-proof place where they could cool. I would usually only do one board at a time, though others sometimes would do two or three if they were small.

This technique works well for one or two of a kind boards that have parts that are manually “pick and placed.” A professional, time-temperature sloped oven is required for high-reliability boards, e.g., those going into space, but few hobbyists have this need.

I’ve never tried it with any ball-grid-array parts. We would send those out to assembly houses that also had x-ray inspection machines that could verify the BGA pins were all soldered.  I also found that it was best to leave off things like 100 lead quad flat-packs, and solder them on by hand. They would seem to invariably get jostled out of position and need to be removed and resoldered by hand anyway.

The larger and thinner the spatula the better. Don’t even think about trying it with any sort of plastic spatula — they’re all way too thick.

I also recommend that you practice on a board with only a dozen or so parts, none of which have more than 24 leads and accept the fact that you’re going to ruin a few before you get the hang of it.

Once you do get the hang of it, you’ll wonder why people are so scared of trying it — it’s really not all that hard!

Clark Jones
Gilbert, AZ

I converted a Black & Decker toaster oven into a reflow oven. Had to split off the cooling fan AC driver to a separate control line. I use leaded solder paste because of the lower melt temp & the eutectic parts to pads alignment. I only do design concept layouts & proof of concept boards.

Gail Schooley
via email


PC Joystick Interfacing Answered November/December 2018

Is it possible to connect a joystick to a microcontroller? PIC, PICAXE, etc. I don't want to have to take apart and hack the joystick. If so, what is required?

#11181
Nick Hulst
Cedar Rapids, IA



Answers

Digging into the far recesses of my memory, the classic PC joystick with the DB15 connector used a resistor pot on each axis. Since ADC was expensive at the start of the ‘80s, IBM opted to use an RC based timer where the R (resistance) came from the Joystick axis and the capacitance was on the MoBo. I’ve not taken one of these apart but having looked at the dev docs it was a matter of resetting an axis, which would charge or discharge the cap and then count to yourself until the opposite state was met. I don’t remember which polarity it used.

With a pair of ADC channels at your disposal it should be way simpler and certainly quicker. You might have to wire resistors in parallel to make a voltage divider. Get your hands on one of those sticks and it should be straight forward to figure out. The buttons were simply switches tied to other pins on the connector.

Jon Foster
Bend, OR

It is possible to connect a joystick to ANY computer/processor that has analog or digital input capability!

The first question to answer is this: ANALOG (i.e., dual XY potentiometers) or DIGITAL (OPEN/CLOSE switches) joystick?

ANALOG joysticks (ala Atari 5200) use two potentiometers (typ. 10K-50K) to send varying voltages (typ. 0-5VDC) to two A/D converters — one for the X axis and one for the Y axis. The applied voltages generate two numbers and the software uses them to position an object on the screen.

DIGITAL sticks (ala Atari 2600/7800) use four ON/OFF switches: UP, DOWN, RIGHT, LEFT. The 4 switches have one COMmon connection (usually DC Ground) and the other switch side feeds a digital input looking for an ON (switch depressed — input grounded) or OFF (switch not depressed — input floating) state. The LENGTH OF TIME the switch(es) are depressed determine object movement and speed of movement (i.e., longer press = increase the speed) and the combination of two depressed switches gives you diagonal movement. The software does all the work in reading the switches and interpreting the action. The paddle controller for the 2600 was a single potentiometer with 1 (or 2?) button switches.

Action buttons (i.e., FIRE button) on the sticks are just ON/OFF switches connected to digital inputs. The majority of Joysticks typically have one action button.

Just do web searches on Atari joystick wiring to get wiring diagrams. The Atari sticks (2600, 7800 and 5200) can still be found, as well as replicas. The 2600/7800 sticks use a DE9S (9-pin female) connector and the 5200 uses a DA15S (15-pin female) connector for interfacing. Interestingly, Apple made an XY joystick for the Apple 2 that used a 14-pin DIP plug to directly connect to a special socket on the motherboard.

Trust me, it’s easier to purchase, or locate at a Goodwill, a pre-built Joystick (analog or digital) rather than try and build one yourself. The Atari type sticks use readily-available D-type mating connectors which are not difficult to wire to your project using the stick’s wiring diagrams as a guide. The great thing with them is they use no more than +5V, making them very safe interface devices.

Ken Simmons
Auburn, WA


Wireless Data To PC Answered September/October 2018

I have a number of wireless temperature/humidity sensors made by Oregon Scientific for use as weather station sensors. I would like to use them for a data acquisition and monitoring application. Does anyone know what frequency and mode they operate on and how I might use them to send data to a PC to record seasonal trends? Would I need a microcontroller to interpret the output or could it be read directly by the PC and then logged and displayed using software such as MakerPlot?

#9184
Jai Hooley
Edmonton, AB



Answers

Oregon Scientific registered with the Federal Communications Commission (FCC) to use 433.93 MHz as the frequency for its units YPGSL109, YPG SL109, YPG-SL109, YPG-SL1O9, YPG-SLI09, YPG-5L109. For only a few dollars you can buy small transceiver modules for the Arduino family of microcontrollers (MCUs), and others.

The arduino could capture raw transmissions and send the data to your PC’s terminal software via a USB virtual serial port. Then you could look at the raw information and decide what it means and how to use it.

Oregon Scientific has published information about its communication protocol and you can find here: wmrx00.sourceforge.net/Arduino/OregonScientific-RF-Protocols.pdf. The SourceForge project has other information and code that might help you: wmrx00.sourceforge.net.

Jon Titus
Herriman, UT


Something Strange With The Range Answered September/October 2018

The effective range of the key FOB for my Ford F150 seems to have decreased over recent months. While it used to work from distances of 75-100 yards easy, now I need to be nearly right in front (10-20 yards) of my vehicle to operate the systems. I changed to a fresh battery, but no difference. Is it likely there is an antenna problem? If so, where is it located and is there a test procedure?

#9183
Les Waldroup
Charlotte, NC



Answers

Yes, that could be the problem, but remember you have two antennas, one is in the car someplace as well.

The FOB is easy to take apart. the antenna is most likely a trace on the circuit card unless it is very old. I doubt every manufacturer uses the same location but the most likely location is going to be at the end you point at the car.

Remember the online posts saying to increase the range of your FOB, point it at your chin? IMHO pointing at your face or chin had nothing to do with increasing the range except that you had to lift the FOB up a bit higher to point it at your chin. I found I could raise the FOB over my head and substantially increase the range. Till you find the problem you might try that as well.

Phil Karras, KE3FL
via email

I had a similar problem with the key fob for my ‘91 BMW. It got so bad that I had to hold the fob against the drivers window for it to work. After trying new batteries and testing the range of the transmitter at the local auto supply, I decided that the problem must be with the receiver which I found up inside the dash behind the instrument panel. After removing the circuit board from its case, I found that there was an antenna matching network with an adjustable inductor on the board that was not sealed. By speculating how gravity and 27 years of thermal cycling might effect the adjustment, I gave it a quarter of a turn in the opposite direction and, as luck would have it, my effective range was restored to over 100 feet. If your unit was factory installed you can probably find a shop manual at the public library to help you locate it and perhaps my fix will work for you. Good Luck with it.

Jack Noble
Shoreline, WA


PCBs With PTHs Answered July/August 2018

Is there a hobbyist method for making circuit boards with plated through holes at home? Also curious by what is meant by multilayer boards. I'm just getting started, so forgive if this is an obvious newbie question.

#7185
Leonelo Márquez
Maplewood, MN



Answers

I gave up making boards years ago. Hazardous chemicals, lots of fiddly fine work. Double side boards require precise alignment, and multilayer boards are impossible at home.

A multilayer board is a board that has conductive layers sandwiched inside the board, usually one for power and one for a ground plane — for a total of four layers (top, ground, power and bottom). More layers are also possible, of course.

Jay R Jaeger
Madison

Etch or mill your circuit boards with space for larger holes where you need them to be plated thru. Insert small grommets made for that purpose into the holes and peen them over. In most cases this will be unnecessary because you can just solder parts like resisters on both sides of the board.

The use of sockets will make working with IC’s, DIP switches, and resister arrays much easier.

Multilayer boards are made up of several thin circuit boards glued together. Four to eight layers are common. The plated thru holes often do not reach the surface of the finished board. You can achieve much of the same effect by adding a daughter board (a shield in Arduino terms), to your design.

Dale Freye
via internet

I don’t know of any easy way to make plated-through holes using home brew PCB etching materials. However, if you use double-sided copper-clad boards, you could make front and back etching screens. Just make sure you securely attach the front etching screen to the blank and re-drill your holes from the front side.

Then, using the drilled holes as a guide, securely attach the back screen to the blank, ensuring you accurately line it up the drilled holes. Then, with both screens still attached, expose both sides of the blank (assuming photo-resist is used), remove the screens, then develop and etch the board.

When you install the components on the front side, ensure you solder both sides of the board where a lead makes a front to back connection.

As for multilayer boards, they’re exactly what the description is. They’re a sandwich of thin boards, each layer typically 1 millimeter thick, with etched circuitry (single or double-sided) or an un-etched power or ground plane, glued together in exact (i.e., 1/10000” or better) alignment so all the through-holes will match-up when components are installed.

When completed, these boards can be as thick as 5 millimeters or so, with 8 or more layers! Most multi-layer boards use through-hole plating, especially on power and ground planes, to ensure positive through-hole connections (again, depending on how well each layer is aligned when the sandwich is made).

They’re soldered using wave-soldering equipment because hand-soldering risks damaging the board via local overheating, especially when soldering to an internal power/ground plane or even bad solder joints (the solder doesn’t make the connection on internal layers), which is why they’re very expensive to design and manufacture.

Ken Simmons
Auburn, WA

Answers to “newbie” questions always help others. You can create plated through holes in your workshop, but it involves many steps with chemical solutions.

Instead of messy and toxic chemicals, why not solder a jumper through the board to connect conductors on both sides? As an alternate, use component leads to make a side-to-side connection and solder the leads on both sides of your board.

If you truly want plated-through holes, contact a PCB fabricator that will make a run of three or four boards for you with plated-through holes. I have used ExpressPCB and a friend has used OSH Park, both with good results.

A multilayer board has etched copper layers sandwiched between insulating layers and connected with tiny plated-through holes. Search Google for multilayer PCB and you’ll find many helpful cut-away diagrams.

Jon Titus
Herriman, UT

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