CheapoModo: quick and dirty transformer snubber bellringer jig - Page 3 - diyAudio
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Old 3rd March 2014, 07:35 PM   #21
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Quote:
Originally Posted by funk1980 View Post
Thanks guys!

Well, to be honest, I've quite literally followed the LTSpice schematic for layout of the components, including the Vcc and GND rail. I'm more than willing to make a picture of the solder-side, but I doubt it'll help much, since it's a veroboard. Let me know.
Well I think it can't harm, it just depends on your eagerness! I think that since it works, it is a follow-me example after all.
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Old 5th March 2014, 09:26 AM   #22
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Ok, but don't bash my vero-board skills

IMG_0414.JPG (3).jpg IMG_0413.JPG (3).jpg
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Old 5th March 2014, 07:43 PM   #23
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Originally Posted by funk1980 View Post
Ok, but don't bash my vero-board skills
Hahaha, be sure that I won't! Nice work, thanks.
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Old 8th March 2014, 02:02 AM   #24
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Today I made a quick PCB layout of a CheapoModo using the single-PNP gate driver circuit. I sent the attached .zip file of Gerber data & got the attached price quote back from OSH Park: $13.75 for 3 boards, and shipping is free (inside the USA anyway). Schematic is attached.

I'll receive the boards back from OSH Park in 2-3 weeks, and stuff+solder them to see whether they work. It's not a complicated design so I think the prognosis is excellent.

If anyone here would like to download the PCB data and order their own boards, here are the files. I suspect you'll have an easy time finding people who'd like to have any & all extra blank boards you're willing to sell or to give away.

BEWARE: the layout assumes an E-B-C pinout of the bipolar transistor (e.g. the 2N3906). The BC547 does not have this pinout. Check your datasheet!
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File Type: png order_from_OSH_Park.png (126.2 KB, 212 views)
File Type: png schematic.png (102.7 KB, 217 views)
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File Type: zip ChModoR1_to_OSH_Park.zip (23.2 KB, 25 views)
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Old 8th March 2014, 02:10 AM   #25
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Hi all, Forgive me if this is a stupid question, but will this device be usable with an old analog scope with no capture functionality. i.e. does it continuously ring the transformer in such a fashion the scope will be able to trigger on it and hold a stable image.
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Old 8th March 2014, 10:08 AM   #26
AndrewT is offline AndrewT  Scotland
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Yes.
But the signal is very narrow and quite low.
You need to use the timing switch to get one cycle on screen after you have found the very narrow resonant peaks.

Then use the expand facility to see the ripple at the peaks.
I use the invert on the trigger to swap between the rising and falling waveforms.

The ripple is present when VR is set to highest (as if the Zobel was not there)
The ripple is present when VR is set to zero (as if the single capacitor was inserted without a snubbing resistor).
I can see the null somewhere in the range from max to min resistance. I am finding a range of resistance from 5r to 500r for a wide range of transformer VA.
I use a 1k VR. But I think I will add a (pluggable) 100r VR for the bigger transformers.

I never got any guidance on how fast the edges need to be with the Cheapo, but my 1us times seem to show the effect.
I don't know if the required resistance values would be different using the fast Quasimodo.
It is 30 to 300 times faster than my version of the cheapo.
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Last edited by AndrewT; 8th March 2014 at 10:12 AM.
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Old 8th March 2014, 03:19 PM   #27
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A reader cautioned me that the 1N5819 Schottky diode may not qualify as a "junkbox part," and he's right. I apologize.

That diode's purpose is to protect CheapoModo in case the user accidentally connects the battery or power supply backwards. A Schottky diode is slightly better in this application because its forward voltage drop is lower, but just about ANY diode, silicon or Schottky, with >15V max reverse voltage, will work fine: 1N4148, 1N400x, BYV26, BA159, whatever's in your junkbox.

And of course you could just install a jumper wire instead of D1. You may not want or need this kind of protection.
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Old 15th March 2014, 03:38 AM   #28
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Well it seems my analog scope has no issues picking up this trace, though i can only just get it to display the initial ring. I didn't even have to use the x10 magnification mode.

In the test images i was using a cheap 5va 6v transformer that came from eBay china. With no Cs capacitor i quickly got the scope dialed in on the ringing, and with a little experimentation i ended up with a 100nf in the Cs position, and the pot set to ~ 55ohms to produce a flat line. It certainly seems to work, now i just need to learn how to use it properly

Cheers Mark!
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File Type: jpg nosnub.JPG (481.3 KB, 177 views)
File Type: jpg snub.JPG (470.2 KB, 162 views)
File Type: jpg cheapomodo.jpg (302.6 KB, 87 views)
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Old 15th March 2014, 04:55 AM   #29
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Does it vary with primary winding that is shorted, open, or loaded with characteristic impedance ?
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Old 15th March 2014, 11:37 AM   #30
AndrewT is offline AndrewT  Scotland
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Yes, the results vary a lot with the untested windings, either open or, shorted.
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