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Phone Text Book Answered April 2012

I am an electrical technician looking for a textbook or reference that deals with landline phones. I am wanting to learn the info that a phone technician would use such as multi-phone land lines, troubleshooting phone lines, and the definitions that are used in the industry.

Please direct me to a text book that would be a useful resource of learning and a good reference for down the road.

Jim Houser
Cambridge, OH



Or just search the web using, "Telephone Technical Reference" to find a bunch more.

Philip Karras
via email

For a book on telephone electronics, see:
ISBN-10: 0750699442
ISBN-13: 978-0750699440

You can find them for about $10 new. There is even a Kindle edition, although it is close to $35.

Pete Lunt
Raleigh, NC

Transformer Answered April 2012

How do I calculate the number of turns for both the primary and the secondary windings of a transformer?

Ibadan, Oyo


Transformer Calculations: www.electrical-design-tutor.com/transformercalculations.html

Transformer Winding: NOTE: There are many types of transformers and you didn't specify what it would be used for: RF-antenna/circuit impedance matching, AF impedance matching, AC Voltage Conversion

A good place to start: The Radio Amateur's Handbook, if you can get one.
Practical (power) Transformer Winding: http://ludens.cl/Electron/trafos/trafos.html

Philip Karras
via email

Get a copy of Coyne Television and Radio Handbook. Very good Practical transformer design, also wire and other charts. I see this book on the Internet book sellers.

Edwin Fitzpatrick W8MFS
Ellijay, GA

Since you are asking about the primary turns, we assume that you need equation (2) shown in the Figure below, and you are experienced enough to already be familiar with equation (3), listed for reference. We also assume that you are interested in rewinding a power transformer (50/60 Hz) rather than an audio or radio frequency transformer. The main task is to get the minimum required number of primary turns without saturating the core, otherwise smoke. Everything else is just details.

An E-core transformer core is shown in the figure. It is constructed from a stack of alternating "E" and "I" shaped laminations of silicon steel. The "not shown" windings go around the center leg through the two windows. The key to the design is the cross-section area of the center leg through which the magnetic lines of flux pass. The Area (Ae) is the width of the center leg (w) times the height (h) of the stack. The Ae determines: 1) the power output capability (Wo); and 2) the number of primary turns (Np). It should be no surprise that a bigger core (Ae) supports more power (Wo). Bigger cores require fewer turns of larger wire than smaller cores.

Start out with either equation 1a or 1b. If you are starting with a known power output requirement (Wo), use 1a to determine the required center leg core area (Ae). Example: A 100 watt (Wo) transformer operated at 60 Hz requires Ae = sqrt(100)/5.58)*sqrt(60/60) = 1.77 sq in center leg core. You then need to select a stack of laminations for which w and h
multiply out to 1.79 sq in, or more.

More likely, you have a discarded transformer on hand that you want to rewind with custom windings. Equation (1b) tells us how much power (Wo) a center leg of a given area will support. Knowing the wattage allows us to select the proper wire sizes for both windings. Example: We have a 1.0 in stack of 1.0 in wide laminations = Ae = 1 sq in: Wo = (60/60)*(squared5.58 * 1.0) = (31 watts).

The minimum number of turns for the primary is given by equation 2 in terms of the primary voltage (Vp), frequency (f), center leg E-core area (Ae), and flux density of 80,000 lines per square inch. Example: Our 31 watt 1.0 square inch core is to be operated at 120 VAC, 60 Hz; Np = (120 * 10e8)/(4.44 * 60 * 1.0 * 80,000) = 563 turns.

If our 31W, 120V, 563 turn primary were to be accompanied by a 12V secondary, the voltage ratio is 1/10. The secondary turns Ns is proportional (equation 3). Ns = 56.3 turns. This is the open circuit voltage. Optionally, if we want the loaded voltage to be closer to 12V, add 5% more turns to the secondary (not shown in equation 3). Ns' = 1.05*Ns = 1.05*56.3 = 59 turns.

What size of wire should be used for our example 31W 120V : 12V transformer? Answer: Choose a wire gauge having approximately 1,000 circular mils of cross-section per ampere of current. See Reference [2] for a wire table. The 120V, 31W primary has I = P/V = 31/120 = 0.26 A current. Closest is AWG #26 wire with 254 cir mils cross-section for the primary. The secondary current is I = P/V = 31/12 = 2.58 A. Closest is AWG #16 with 2583 cir mils.

Note: The above formulas based on Reference [1] predict a full load temperature rise of 50 degrees C. If this is too hot for your application, decrease the flux density of 80,000 lines per square inch by 20%.

Practical considerations: In the olden days, it was possible to disassemble a transformer by removing the bolts compressing the lamination stack, then knocking out the laminations with a hammer and screwdriver. These days, disassembly may be impossible due to epoxy applied to the laminations. If possible, recover the insulating form on which the coil is wound from your scrapped transformer. This is a hard-to-make item. If you are modifying a not-burned-out transformer, only remove the secondary; re-using the primary.

Some small transformers — like the open frame RadioShack products — may have a large enough window space remaining to add windings atop the existing secondary. If you only need a few volts, or want to add a few volts to the existing secondary, the turns may be threaded through the windows without disassembly. Temporarily, tape sharp window edges to prevent scraping the wire while threading.

[1] Reference Data for Radio Engineers, 4th ed, “Design of Power Transformers for Rectifiers,” pp 25, 1964, ITT.
[2] Lessons In Electric Circuits, Vol 5, Ch 3, Copper wire gauge table, www.ibiblio.org/kuphaldt/electricCircuits/Ref/REF_3.html.

Dennis Crunkilton
Abilene, TX

Here are three video tutorials on building a transformer from an old microwave. They go into the design and windings design pretty well (alternative: just go to youtube.com and search on "mot salvage tutorial"):




Pete Lunt
Raleigh, NC

The question about transformers does not admit to a simple answer. The primary and secondary windings are applied such that the ratio of the number of primary and secondary turns is identical to the ratio of the primary and secondary voltages. However, the above statement presumes an ideal transformer. It also presumes that the designer has already considered the frequency and waveform of the voltage applied to the primary winding, heating, and safety considerations, etc. This knowledge is required in order to permit the designer to select the proper type and physical size of the transformer core material, the bobbin construction, and other matters.

If your interest is constrained to power-frequency transformers — principally 50 Hz in your part of the world — I found an interesting treatise at http://ludens.cl/Electron/trafos/trafos.html. His complementary article at http://ludens.cl/Electron/Magnet.html discusses the underlying physical properties relative to transformer design.

Peter A. Goodwin
Rockport, MA

Half Cycle Magnetizer Answered April 2012

I would like to find a schematic for a half cycle magnetizer. The one that I have runs on three phases but I need one that runs off of the 120 volt line at 60 cycles. The working load that I need is about 5" x 5" x 4" or bigger. The specs for the output coil and the fast solid-state switch are most important. I realize that the magnetizer must be enclosed with non-magnetic material and probably uses a big heatsink.

Bob Macias
Fernandina Beach, FL


Check out the Oersted Technology article at http://oersted.com/magnetizing.PDF.

Peter A. Goodwin
Rockport, MA

Bird Sound Circuit Answered May 2012

About 40 years ago, I built a bird sound kit and put it in a Sucrets® metal box (same size as an Altoids® tin). I don't remember the name of the company, but the circuit was a blocking oscillator. I believe it had a miniature audio transformer; one side had a center tap. I think it only had one transistor and ran on a single AA cell. I used a 1" speaker with a clear plastic diaphragm. You switched it on and it made a realistic repeating bird chirp. Better yet, if you lightly touched the speakercone, the sounds changed to other types of birds because of the change in reactance of the speaker. It was quite loud. Does anyone remember this and have a schematic?

Charles Foreman
Glendale, CA


The schematic and parts list shown below is from the three page article “The Solid-State Bird,” by John Simonton, Jr. It appeared in Popular Electronics Spring 1973 “Electronics Experimenters Handbook.” (A scanned PDF of the entire article can be viewed or downloaded here also.) The foil pattern measures 2 7/16" x 1-3/4", or 71 x 44 mm. While searching, I also ran across two additional "bird sound" circuits: Dec. 1981 Radio Electronics "Electronic Bird Chirper" — four transistors, total 25 parts; and 1993 Popular Electronics Electronics Handbook "Hot Canaries" two LM324s, one transistor, two 1N914 diodes total 54 parts (no critical parts; parts count includes 9V battery, switch, and speaker).

Edwin Hampton
Mattoon, Il

I remember using a SN76488N 'sound generator' to build 'sound' circuits, such as train whistles, crowds cheering, birds chirping, and sirens, etc., for electronic games and other projects, but then I started to think about producing sounds as realistic as possible but in a less complicated way. Here's a possible solution that you might want to consider. I went to RadioShack and purchased a few of those handheld voice recorders [available at www.tmart.com] that allowed about a 10 to 15 second recording time. Pressing one button allowed recording, and pressing another button allowed audible playback. Removing a few screws, I simply wired a micro-switch in parallel with the playback switch and, when pressed, could instantly and repeatedly hear what I had recorded until I recorded over it with something else. I wired the output of the recorder to the input of a small audio amplifier [using an LM386 IC circuit] for a clear and loud output. I wanted a crowd cheer each time a hit was made and a trumpet blare every time a man crossed home plate in my electronic baseball game. I was fortunate enough to have these realistic recorded sounds already programmed on my Technics keyboard. I simply pressed the record button, recorded the sounds, and then wired the recorders into the game. You can easily record real bird sounds for your project. You can store all bird calls into a memory chip and then play back, record, and use as needed.

John Mastromoro
via email

Looking For Datasheets Answered May 2012

I have a collection of one and two Meg memory strips from early PCs, with which I would like to make delay lines for digitized audio. I can find no application or pin-out data for the chips; the markings seem inconsistent from strip to strip, and have no manufacturer's name or logo. (I have one set of what I believe to be four Meg strips designated as MT4C4ME8DJ.) I've done Google searches for this style of memory chip to no avail. Can anyone help?

Arne Berg
Huntington Beach, CA


This is an old EDO SIMM.
Knowing that — and knowing that MT meant Micron — I did a Google search for "micron edo memory datasheet" and found: www.pjrc.com/mp3/simm/datasheet.html which says (among other things):


For the latest datasheet revisions, please refer to the Micron website: www.micron.com/mti/msp/html/datasheet.html.

• JEDEC- and industry-standard pin-out in a 72-pin, single in-line memory module (SIMM)
• 16 MB (4 Meg x 32) and 32 MB (8 Meg x 32)
• High performance CMOS silicon-gate process
• Single 5V ±10% power supply
• All inputs, outputs, and clocks are TTL-compatible
• Refresh modes: RAS#-ONLY, CAS#-BEFORE-RAS# (CBR), and HIDDEN
• 2,048 cycle refresh distributed across 32 ms
• Fast Page Mode (FPM) access or Extended Data-Out (EDO) Page Mode access

Options                         Marking

50 ns access                     -5*
60 ns access                     -6
72-pin SIMM                        M
72-pin SIMM (Gold)             G
Operating Modes 
FAST PAGE MODE           None
EDO PAGE MODE                X

*EDO version only

Part Numbers
EDO Operating Mode
Part Number               Configuration            Plating

MT8D432G- x X                4 Meg x 32                  Gold
MT8D432M- x X                4 Meg x 32               Tin/Lead
MT16D832G-x X               8 Meg x 32                  Gold
MT16D832M-x X               8 Meg x 32               Tin/Lead
x = speed

FPM Operating Mode
Part Number               Configuration            Plating
MT8D432G-x                    4 Meg x 32                  Gold
MT8D432M-x                    4 Meg x 32               Tin/Lead
MT16D832G-x                  8 Meg x 32                  Gold
MT16D832M-x                  8 Meg x 32               Tin/Lead
x = speed

Pin Assignment (Front View) See diagram below.
72-Pin SIMM
4 Meg x 32
8 Meg x 32

PIN    SYMBOL      PIN     SYMBOL        PIN     SYMBOL         PIN     SYMBOL
1         Vss              19          A10              37          NC                 55       DQ12
2         DQ1              20          DQ5             38          NC                 56       DQ28
3         DQ17            21          DQ21           39          Vss               57       DQ13
4         DQ                22          DQ6             40          CAS0#          58       DQ29
5         DQ18            23          DQ22           41          CAS2#          59       Vdd
6         DQ3              24          DQ7             42          CAS3#          60       DQ30
7         DQ19            25          DQ23           43          CAS1#          61       DQ14
8         DQ4              26          DQ8             44          RAS0#          62       DQ31
9         DQ20            27          DQ24           45          NC/RAS1#*   63       DQ15
10       VDD              28         A7                46          NC                 64      DQ32
11       NC                 29         NC (A11)      47          WE#              65      DQ16
12      A0                  30         VDD             48          NC                 66      NC
13      A1                  31         A8                49          DQ9              67       PRD1
14      A2                  32         A9                50          DQ25            68       PRD2
15      A3                  33         NC/RAS3#*  51         DQ10             69       PRD3
16      A4                  34         RAS2#         52          DQ26            70       PRD4
17      A5                  35         NC                53          DQ11            71       NC
18      A6                  36         NC                54          DQ27           72        Vss

*32 MB version only

If this isn't the right part, then try www.alldatasheet.com/view.jsp?Searchword=MT4C4ME8.

Rusty Carruth
via email

LED Chaser Answered May 2012

I need a schematic for an LED chaser for an atomic model my class is building. I will be using about eight to 16 LEDs. They need to be adjustable in cycling and speed. Could this circuit be expandable from, say, four to 40 LEDs?

Robert Slusher
Santa Fe, NM


First, I would recommend checking out the ‘Chaser Light Marquee’ in Smiley’s Workshop here on N&V.

If that doesn’t work for you, I would recommend building something with presettable shift registers, aka parallel-in parallel-out shift registers.

There are a number of different versions of those, the 74198 and 74199 are TTL versions, and there is the 4035 which is a CMOS version (4 bits per chip).

The idea is, string enough of those together to have the number of outputs you want, then use switches to set the input states (thus which LEDs are lit on startup).  Tie the last used output bit to the serial data input of the first chip if you want the data to cycle around once loaded.  If you would rather the pattern get reloaded once all bits are shifted out then you need a way to reload when terminal count is reached (a comparator or just an up or down counter).

Once the data is latched, let the clock run at your shift rate and you’re done.

You need a clock (555 for example) and a way to load the register(s) upon powerup.

Rusty Carruth
via email

By "LED chaser," I assume you mean a circuit that will light a series of LEDs one at a time in a sequential and cyclic progression. You can accomplish this using the MC14017 Decade Counter IC (download a datasheet from www.onsemi.com). A single MC14017 will provide 10 LED outputs. Figure 3 in the datasheet illustrates how to wire together several MC14017s (with the help of MC74HC08 AND gates) for obtaining more outputs (40 LEDs will require five MC14017s). You can drive the LEDs directly from the MC14017 outputs with a series resistor (~ 470 ohms).

You'll also need an oscillator source, and an LM555 is the easiest way to do this. A convenient calculator for determining component values is available at www.coolcircuit.com/tools/ne555_calculator/index.php. You can use a potentiometer to make the oscillator frequency variable. If you make the frequency 10 Hz, for example, each LED will light for 0.1 seconds, and it will take one second to cycle through all 10 LEDs.

All the components you will need can be ordered from Jameco (www.jameco.com). You can use the 74HC4017, 74HC08, and LM555, and any size/color LED you like. The figure below is a basic schematic diagram to get started.

Bob Stewart
via email

Display Advice Answered May 2012

I need to build a high visibility display unit that consists of 15 1” x 1-1/2” display units. I've considered LEDs, Electrolum panels, and more. I cannot seem to find a display unit that can properly display true black and true white. I also need them to do at least 256 colors as well — nice, rich high resolution colors. Is there such a thing? I believe I've seen them but am not sure where since I go to a lot of places displaying a lot of stuff.

Tom Moore
Beverly Hills, FL


The only displays I’ve seen recently are basically ‘VGA flat panels’ or LCD flat panel displays. Expensive, but with LED flat panels you should get pretty close to real black and real white…  (for example, at the local Pei Wei they have large 50” flat panel TVs for their displays, and the local credit union I use does a similar thing). Here are a few companies that sell such things.


Displaytech (www.displaytech-us.com/?gclid=CKXvjJXo9q8CFSoZQgod60iTUg)


Purdy (www.purdyelectronics.com/products/displays/tftmodul.cfm)


IDT (www.toshibadisplays.com/?_kk=LCD%20display%20panels&_kt=41098ecd-8c7b-4102-b602-a2891f16f4c3)


Planar (www.planar.com/?campaignID=70150000000TpWT&_kk=planar%20displays&_kt=77205abe-b0e5-448e-ad71-fdd9273e5e74&gclid=CP6Nrabo9q8CFcYBRQodDXzDDA)

Rusty Carruth
Tempe, AZ

Good luck finding a display that actually displays black. About the only thing that would come close is an "electronic ink" display as used on an Amazon Kindle. Most displays — whether CRT, LED, incandescent, etc. — generate light. Black is the absence of light and with a CRT (picture tube) or LED display, the blackest black you're going to get is with the display off. It only seems "black" in the presence of all the contrasting colored light around it. Look at your TV with power off. That's its blackest black. Really! It doesn't seem that your "256 colors" is a good definition of "nice, rich, high-resolution colors." Your local paint store has more color chips than that by far and it's certainly not "high resolution."

Dean Huster
Harviell, MO

DTMF Encoder Answered June 2012

Where can I find a schematic or kit for a 16 button keypad encoder, without having to program a PIC? That's a regular telephone keypad plus A - D on the right side.

Terry Arnall
Hayward, CA


Go to www.jameco.com and search for part number 32803. It is a DTMF Generator number TCM5089. Click on one of the three data sheet options to download and print the PDF.

Dennis Hewett
Frontenac, KS

Try searching on eBay for "DTMF encoder." I found more than a few there, but they aren't cheap.

DTMF ENCODER GENERATOR *** $34.00 *** 11 Days



While these will all probably be sold before you read this, you'll most likely find others. I'd ask the "Electrical_Components_Supplies_ET" place since they may have other chips.

Philip Karras
via email

The IC for DTMF encoding is a TP5089 from National, or a second source is TCM5089 from Texas Instruments.

It is available from Jameco (Jameco.com) as TP5089; their item #32803.

It's listed as available from stock on their website. You can also download datasheets from them to check before ordering.

Don Pomeroy
Manchester, NH

FFT Audio Spectrum Analyzer Answered June 2012

How can I implement FFT in microcontrollers so that I can do a frequency analysis of incoming audio signals that I have sampled through the A/D converter? I am not getting just where to start, though I know mathematical techniques of FFT. I want to deploy a cool audio spectrum analyzer for my audio system using matrix LEDs.

Abhishek Kumar
Meerut, Uttar Pradesh, India


I googled "audio FFT for PIC libraries" and got several hits for arduino and Rpi libraries Give it a try, I think you will find what you're looking for.

William B Runyon Sr
Chesapeake, VA

Compressor Starter Answered June 2012

I am looking for a positive temperature coefficient motor starter for a compressor. Or, I need help using different parts such as a single pole contactor/relay for a hard start. The part I want to replace has the following number: RF-6850-18, and consists of a PTC starter and an overload protector. Can I replace this with a hard starter contacter? I can photocopy the schematics and email anyone who can help me.

Michael Farley
Cincinnati, OH


The original part is shown at www.repairclinic.com/PartDetail/Start-Device/RF685018/1569121.

The three terminals on the device are C, S, and R. C is connected to the COMMON of the compressor, with S being START winding, and R being RUN winding.

I'd suggest replacing the original device, and adding the proper MARS hard start device to kick the compressor. You don't want to bypass the overload! PERIOD!

MARS Motors & Armatures, Inc.,  has hard start devices and torque multipliers for refrigeration/AC compressors. I've used a smaller MARS hard start device on several refrigerators, and they work fine. (www.marsm-a.com/CGI-BIN/LANSAWEB?WEBEVENT+R06630136135017015394091+ML6+ENG).

I can't find the paperwork on the last MARS device I purchased. Any local HVAC distributor should be able to locate what you need, depending on the compressor size. It's just a two wire hookup.

I'm including a PDF document from MARS and my refrigeration document for you to view.

Larry Kraemer
via email

I work for a major appliance repair company/retailer. Replacing the factory compressor start device with an after-market hard start kit is not recommended. Most of those kits — if not used or sized correctly — can cause permanent compressor failure. I would suggest trying to source the correct part by model and serial number of the refrigerator. There is a major appliance parts dealer in Cincinnati and Dayton that can help. If you can not find a model or serial, I suggest Whirlpool part number 8201786. This kit covers several different compressors, as well as wiring connections.

Sean Battito
Mohnton, PA

I've bought PTC starters for refrigeration compressors from www.repairclinic.com on a few different occasions. A local appliance shop with a parts counter should be able to supply them too, either OEM or a universal replacement. The "hard start" kits you can get are nothing more than a standard PTC starter, overload protector, and capacitor stuffed into a housing. The one time I tried one of those, it failed within a few weeks.

If you want to try rolling your own, this schematic is said to work although I've not personally tried it. Digi-Key, Mouser, and other electronics distributors carry a selection of PTCs and bimetal circuit protectors that could be used.

James Sweet
via email

Go to any well stocked refrigeration supply house and ask for a universal compressor starter.

This will be a device with leads. (I have no idea what's inside.) Connect it as shown on the package, removing the existing starter device.

These things work every time. Be sure to leave any original thermal protective device intact.

They can also be used on small air compressors that use PTC devices as starters.

Don Pomeroy
Manchester, NH

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