A little tester to determine transformer PhaseDots with no scope or signal generator - diyAudio
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Old 8th June 2015, 12:24 AM   #1
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Join Date: May 2011
Location: Silicon Valley
Default A little tester to determine transformer PhaseDots with no scope or signal generator

Transformer schematics include "Phase Dots" that indicate which ends of the windings are in phase. Unfortunately, many transformers in used equipment are not marked with phase dots, and quite a few new transformers are not marked either.

If you have a signal generator and an oscilloscope, it's easy to determine the phase dots: see the first picture. If scope channel2 is "right side up" compared to channel1 then winding2 is in phase with winding1, and "?" becomes a dot. And vice versa. However, some DIYers don't have a signal generator and a scope, so this little tester board called "PhaseDots" might help.

It operates on the same principle, but instead of a scope and human eyeballs, the circuit uses a phase detector (XOR gate) to decide whether the windings are in phase or out of phase. This lights up either a Green LED (in phase) or a Red LED (out of phase). Simple and unambiguous. The circuit schematic is picture#2.

A 555 timer/oscillator drives a square wave into transformer winding#1. The resulting waveform on winding#2 is amplified in a series of CMOS logic inverters (gain > 5x per stage) and compared in XOR gate U1C. If they're in phase, D4 lights up. If not, D3 lights up. RC pulse shapers with slow risetime and fast falltime, drive the LEDs.

In practice the tester board is simple to use. Connect one of the transformer's primary windings to connector P2 (labeled WINDING_1) and leave it connected. Then, one by one, connect all the other windings to connector P3 (labeled WINDING_2) and observe their dots. Write these on a schematic as you go. After the last winding: Boom, you're done!

It is important that the PhaseDots tester should always drive a transformer primary winding. (I.e. always connect a primary winding to WINDING_1). Why? Because transformer primary windings have sufficiently high self-inductance to ensure a long (L/R) timeconstant. This prevents the winding from behaving as a differentiator, ruining the input waveform and lighting up the wrong LED (or both LEDs).

Picture 3 attached, shows the PhaseDots tester connected to an Antek AS-2222 toroidal transformer. Red and black are a primary winding, blue and green are a secondary winding. The illuminated green LED tells us that if red has a Phase Dot, then so does blue.

A few other pictures are attached, showing the PCB that I laid out. There's also a set of Gerber files that anyone can send to a PCB fab (I recommend PCBshopper.com to help you choose a fab) and have their own boards made. The Gerber files are included in a zip archive, along with a Bill Of Materials and other ancillary stuff.

I built several PhaseDots boards for my own use, but I've got some leftover boards and leftover kits of parts which I am willing to let other DIY hobbyists have at my cost.
PCB only: {$6 ship to USA} {$9 ship to CAN+MEX} {$12 ship to rest of world}

PCB + kit of all parts: {$13 ship to USA} {$16 ship to CAN+MEX} {$22 ship to rest of world}
However, I will only accept cash or checks. Fortunately I will accept a check drawn on a non-USA-bank and denominated in non-USA-currency.

Sorry, I will not accept PayPal. I will not accept wire transfers. I will not accept Western Union. If you want to set up a little re-distributorship that does accept these, so you can forward boards and kits to other DIYers, please go right ahead with my blessings and good wishes.

Anybody who wants a board or a board + kit of all parts, send me a Private Message ("send me a PM") for purchasing information, mailing address, etc. I've got approximately twenty of them to get rid of.

Hope you enjoy the PhaseDots tester!
Attached Images
File Type: png PhaseDots_Principle_of_Operation.png (10.0 KB, 508 views)
File Type: png PhaseDots_schematic.png (37.9 KB, 509 views)
File Type: jpg PhaseDots_In_Operation.jpg (423.4 KB, 501 views)
File Type: jpg PCB_photo.jpg (505.3 KB, 480 views)
File Type: png front.png (32.6 KB, 465 views)
File Type: png back.png (31.4 KB, 114 views)
Attached Files
File Type: zip PhaseDots_Gerbers_and_Everything_Else.zip (171.4 KB, 34 views)

Last edited by Mark Johnson; 8th June 2015 at 02:58 PM.
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Old 8th June 2015, 08:48 AM   #2
DF96 is offline DF96  England
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I don't think I have ever seen a transformer marked with "phase dots". They are a circuit diagram convention, not a component labelling convention.
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Old 8th June 2015, 12:02 PM   #3
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Great tool, love that you keep it open source and include the gerbers

Never seen an antek transformer.. if the circuit is printed as a label on the transformer with colour/pin# to phase dot? (maybe i'm missing the joke )..
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Old 8th June 2015, 12:04 PM   #4
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Quote:
Originally Posted by DF96 View Post
I don't think I have ever seen a transformer marked with "phase dots".
Let me introduce to the Antek AS-3218. Here is a color photo of the actual transformer itself, and a snip from the (black and white) datasheet on the manufacturer's website. Look for the blue arrows that I drew upon the photo.
Attached Images
File Type: jpg Antek_AS3218.jpg (860.0 KB, 214 views)
File Type: png datasheet.png (121.0 KB, 203 views)
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Old 9th June 2015, 11:08 AM   #5
Ghianni is offline Ghianni  Greece
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Default Tester

@ Mark Johnson

Hi,

I have sent you a PM, have you received it.

Regards.
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Old 9th June 2015, 11:20 AM   #6
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Nice, i would take one if you would accept payment in a 21st century format.
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Old 9th June 2015, 01:04 PM   #7
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Join Date: May 2011
Location: Silicon Valley
It's true that only accepting checks and currency makes the transaction convenient for me and perhaps inconvenient for buyers. Fortunately you do have several options:
1. Simply forget about PhaseDots. Three days ago you hadn't heard of it and you didn't want it. You were happy and contented without it. Continue on that PhaseDots-free path of life and remain blissfully satisfied & happy.

2. Have the PCB fabbed for you. Post#1 contains the Gerber files which is all you need to order some PCBs. Just now I got a quote from PCB shopper dot com (4.9cm x 9.9cm, qty=10) of $1.85 per board including shipping to the US. Then buy the parts from your local shop or distributor. (BOM is in post#1). Easy. Build one or two boards and give away or sell the others.

3. Wait until someone creates a re-distributorship, buying boards and kits of parts, then re-selling them to you. Don't laugh, it happened (twice) with Quasimodo boards. Two different diyAudio members set themselves up as vendors of Quasimodo PCBs + kits of all parts, and accepted PayPal / BitCoin / Western Union / etc as payment.
I'm selling these at my cost, with zero profit (and my cost is low because I got the quantity=50 discount). If you'd prefer to wait until somebody starts selling them for a profit, you have that right. Remind yourself how much inconvenience and risk you have avoided, and remind yourself that the extra time and extra cost are quite acceptable.

_
Attached Images
File Type: png From_Post_Number_1.png (45.9 KB, 161 views)

Last edited by Mark Johnson; 9th June 2015 at 01:16 PM. Reason: formatting!
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Old 9th June 2015, 01:20 PM   #8
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Quote:
Originally Posted by Ghianni View Post
I have sent you a PM, have you received it.
Yes and I replied just now (Tuesday 09_June , 1620 Athens time)
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Old 9th June 2015, 03:19 PM   #9
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Join Date: Feb 2012
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That wasn't just flippant remark meant to irritate you, i was being serious.

I always take note of windings phase, something i had to get in the habit of doing in a 240v world where i almost always have to wire primarys in series, so i make the effort to match the secondary side while i am at it, and if necessary use a scope to work it out if datasheets and wire colours dont indicate the start of each winding. I do appreciate the work you put into your projects, i made a version of your quasimodo which i use on every project now to work out snubber values, this looks like another useful tool for the toolbox.
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Old 9th June 2015, 04:00 PM   #10
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A bunch of people purchased a Quasimodo PCB + kit of all parts, using currency. Maybe one or more of them might reply to you (assuming they're still subscribed!), if you ask on the Quasimodo thread: "Why did you decide to buy with currency? Now that the transaction is completed, do you regret using currency? Overall, are you pleased with the outcome?" and so forth.
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