Tech Forum Questions

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

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.

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 (A_e) is the width of the center leg (w) times the height (h) of the stack. The A_e determines: 1) the power output capability (Wo); and 2) the number of primary turns (Np). It should be no surprise that a bigger core (A_e) 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 (A_e). Example: A 100 watt (Wo) transformer operated at 60 Hz requires A_e = 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 = A_e = 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.
 

References:
[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.

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"):
 

www.youtube.com/watch?feature=player_embedded&v=KRoPHKpCYmg

www.youtube.com/watch?feature=player_embedded&v=YX3mYO-BIuQ

www.youtube.com/watch?feature=player_embedded&v=-NLy-LL_TGQ

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.

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

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):
 

4, 8 MEG x 32 DRAM SIMMs (OBSOLETE)
DRAM MODULE
MT8D432(X)
MT16D832(X)
 

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

FEATURES
• 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
Options                         Marking
Timing 
50 ns access                     -5*
60 ns access                     -6
  
Packages 
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.

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).

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.

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.

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.

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)

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."

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.

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
www.ebay.com/itm/DTMF-ENCODER-GENERATOR-/400302522698?pt=LH_DefaultDomain_0&hash=item5d33e3c14a

HT9315C HOLTEK DTMF MULTIFUNCTION ENCODER CHIP *** $3.89 *** Only 1 day
www.ebay.com/itm/HT9315C-HOLTEK-DTMF-MULTIFUNTION-ENCODER-CHIP-/150826386913?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item231df405e1

DTMF ENCODER KIT WITH 16 KEY KEYPAD + TX KEYING OUTPUT *** $30.32 *** 10 days
www.ebay.com/itm/DTMF-Encoder-kit-with-16-key-Keypad-TX-keying-output-/270993370582?pt=LH_DefaultDomain_3&hash=item3f1876add6

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.

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.

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.