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User avatar
By PSIG
#24681
Old Grey wrote:
Sat Mar 03, 2018 2:24 am
I tried to make all the designs similar so you can see the differences easily, but must have got dazq's D12 Zener upside-down.

Page 3 pic and upload file has been corrected.
Excellent, OG. Thanks for your work on all that. Actually, I was referring to the photo circuit (and now your corrected version) in my comment. It's all good, and it would work either way, so don't fret any about it.
8-)
David
User avatar
By Ceeloo Yello
#24684
Old Grey wrote:
Sat Mar 03, 2018 2:24 am
I tried to make all the designs similar so you can see the differences easily, but must have got dazq's D12 Zener upside-down.

Page 3 pic and upload file has been corrected.
Yeah thanks for all your hard work.
By romP44
#44329
Hello,
I'm creating a PCB using DAZQ schematic. It will be used on a 12V negative coil terminal.
What do you thing about it?
Attachments
schematic.PNG
schematic.PNG (16.9 KiB) Viewed 1429 times
PCB.PNG
PCB.PNG (55.64 KiB) Viewed 1429 times
User avatar
By PSIG
#44337
[EDIT] Nevermind; I see I already mentioned the Zener a few posts back. However, I'd still like to hear thoughts from others.

Offhand and without cross-checking, it looks OK, and we know the basic circuit is functional. I've always wondered about it though, that in the inline configuration, the Zener diode only reduces the signal voltage by 5.1V — not to 5.1V. It would seem this was overlooked somewhere in the original dev for MS, and just was never addressed because it "worked"? :? I'd like to hear more comments about this from others, just out of curiosity, and possibly circuit improvement.
User avatar
By Kenai
#44340
turboedge wrote:
Mon Jul 20, 2020 6:46 pm
PSIG wrote:the Zener diode only reduces the signal voltage by 5.1V — not to 5.1V
Do you suppose it was designed as a filter of sorts so that signals below 5.1v would not be allowed through?
It looks like is not allowing to pass anything below 5.1v. as you described. :ugeek:
User avatar
By PSIG
#44351
I do not want to hijack the thread, but it is specifically about the opto input topic, so… Indeed it can be used as a filter, but at 5.1V is not blocking much and certainly not any coil voltage ringing, permitting multiple pulses after coil discharge. Hardly worth having at that level. To prevent multiple triggers past the Zener per coil firing, the voltage should be much higher. The 24V in MS3 is the right direction, but still low enough to require cap damping. The capacitor comes-in at that point to dampen the additional pulses as the 2nd part of the filter. But, that filter would not be necessary (though I would still have it for more reasons) to dampen multiple ringing triggers if the Zener were of higher voltage, no? Check my thinking, please.

To the point - if the Zener voltage were much higher, all of the ringing could be entirely avoided for a single clean pulse. That would make the Zener worthwhile. Either high enough to clip the ringing (green line below), or high enough to miss the coil burn and spike (red line). Then the cap is only tuned to provide a smooth signal from the primary flyback pulse and blocking noise without dealing with larger ringing pulses. Alternatively, filter or clip with a different method. Borrowed 'scope trace due to laziness:
ign_pri_sec_voltage.JPG
ign_pri_sec_voltage.JPG (222.31 KiB) Viewed 1361 times
By dazq
#44360
romP44 wrote:
Mon Jul 20, 2020 1:48 pm
Hello,
I'm creating a PCB using DAZQ schematic. It will be used on a 12V negative coil terminal.
What do you thing about it?
I haven't checked it over but nice to see a PCB design.
The circuit is tried and tested and works fine for distributor coil trigger pickup.
I have also used it to provide a tacho (5v type) signal for epas ECU.
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