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Handbook Sync Circuit

PostPosted: Fri Aug 03, 2018 1:42 am
by FlyMario
I wanted to know if any of could maybe answer a couple questions about this circuit.
Sync Circuit.jpg
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I like this circuit and have used the portion at IC1b to grab the sync signal. I am using 5v instead of 12v.

But I am puzzled why we would put a capacitor (C2) on the video line. Wouldn't that mess up the signal some? Stretch out parts?

IC1a speaks of restoring the signal. Is that going to affect IC1b? That part of the circuit is puzzling me. Are we trying to amplify the signal?

It seems I should be able to remove IC2 and just have a logic level Mosfet fire off of the positive signal line (going into pin 3 of IC2).

I am planning to use 6 super bright Led's as that circuit has. would you use 1w resistors there? The positive would be coming from 12v.

I am not an analog guy really and I am trying to navigate to some degree. I know that a lot of circuits are made for regular Mosfets and not logic level ones.

Thanks for any advice you might be able to offer.

Re: Handbook Sync Circuit

PostPosted: Fri Aug 03, 2018 2:51 am
by smeezekitty
But I am puzzled why we would put a capacitor (C2) on the video line. Wouldn't that mess up the signal some? Stretch out parts?

It blocks DC that might be on the video signal. Capacitors in series pass AC unchanged just as long as they are large enough for the desired frequency response.

IC1a speaks of restoring the signal. Is that going to affect IC1b? That part of the circuit is puzzling me. Are we trying to amplify the signal?

It is a DC restore circuit. So maybe(?).

It seems I should be able to remove IC2 and just have a logic level Mosfet fire off of the positive signal line (going into pin 3 of IC2).

Pin 3 will have an analog DC restored video signal. You can certainly use a MOSFET amplifier but you have to make sure it is biased correctly.

I would personally tend to stick with the circuit from Klaas Robers or something like it for the LED driver + DC restore. And then use a separate circuit for sync sep
At least, that is what I did

Re: Handbook Sync Circuit

PostPosted: Fri Aug 03, 2018 3:51 am
by FlyMario
http://www.nbtv.wyenet.co.uk/SingleTran ... driver.pdf

I believe you are talking about this circuit correct? I kind of like having the two functions separate as well. Sync and Led Driver.

The Mosfet on this circuit seems Logic level so I should be able to replace it with my normal Mosfet. Nice circuit.

Re: Handbook Sync Circuit

PostPosted: Fri Aug 03, 2018 11:06 am
by Robonz
The video signal is AC e.g it will go plus and minus 1 or 2 volts for example. The circuit is DC with only one power rail, so the AC signal must be moved across to the DC domain so it goes from say 2 to 4 volts as an example. This requires AC coupling C2 and DC restore IC1a and D1.

R1 and R2 will need to be changed for 5v to give a good sync. You could put a 47K pot in there to replace both resistors. Make sure you do not cheat, C1 must be fitted across the IC1. R4 is the hysteresis and can be adjusted if you are getting noisy extra sync pulses.

IC2 does amplify and adjust the black level. Seeing as you like digital and you are using an Arduino you could scrub all that and feed the video (IC2 pin 3) into the Arduino ADC pin. Convert that to PWM (just a couple of lines of code) and that could drive your mosfet with say 10 ohms on the gate.

It is quite possible you could extract the sync within the Arduino too using its built in analog comparator, or ADC. But get it going first.

Cheers
Keith

Re: Handbook Sync Circuit

PostPosted: Fri Aug 03, 2018 12:32 pm
by FlyMario
Thanks! I think I have enough info to get going. Hope to soon have my motor trying to chase the sync signal.

Really happy with the Parchment paper as a defuser. I moved my leds about 75mm back away from the screen. Figured that would help as well.

Re: Handbook Sync Circuit

PostPosted: Sat Aug 04, 2018 3:05 am
by FlyMario
So I am using the circuit as well as I can.

My Circuit.jpg
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I definitely see the importance of C1. I didn't have a cap that matched that. I did order the correct cap, 1m resistor and diode called for. Will be here this evening. I am never that certain how much you can alter these circuits. The signal seems pretty nice when you go in close but if you stretch the scope out you see missing samples. I am not sure if that is just the effect of the DSO sample rate. I adjusted the pot and could not get that to clear up.
missing teeth.jpg



Another thing that seems strange is that the trigger seems to be out of time with the inbound signal. I figured the reaction time would be much faster. Is the cap on C1 causing that you think? Looks like something is charging.

Trigger.jpg

Re: Handbook Sync Circuit

PostPosted: Sat Aug 04, 2018 5:08 am
by smeezekitty
That is not a scope artifact. The average level of the signal varies because of the AC coupling of the audio output. In some cases, the syncs are not negative enough to trigger the OP amp. I used a pot to adjust the voltage on the non inverting input of the op amp to adjust the threshold. I found that there is a point that will work for most signals without dropping syncs. That point isn't 0V

viewtopic.php?f=1&t=2557#p23422

Re: Handbook Sync Circuit

PostPosted: Sat Aug 04, 2018 8:28 am
by FlyMario
All of the caps on that circuit are meant to be ceramic right? Not cans? Hmm Seems obvious to me that they would be those ceramic ones. I got all puzzled cause I saw someone make an audio amp on youtube and used cans... makes no sense to me.

Oh ... if you ever want to feel sorry for a LM358 ... I mean truely sorry... watch this video. I could never...

https://youtu.be/5UKc3OELRPQ

Re: Handbook Sync Circuit

PostPosted: Sat Aug 04, 2018 10:14 am
by smeezekitty
FlyMario wrote:All of the caps on that circuit are meant to be ceramic right? Not cans? Hmm Seems obvious to me that they would be those ceramic ones. I got all puzzled cause I saw someone make an audio amp on youtube and used cans... makes no sense to me.

Oh ... if you ever want to feel sorry for a LM358 ... I mean truely sorry... watch this video. I could never...

https://youtu.be/5UKc3OELRPQ

Ceramic or film caps. Doesn't really matter. You generally only need to use electrolytics for higher values

Re: Handbook Sync Circuit

PostPosted: Sat Aug 04, 2018 12:04 pm
by FlyMario
You know... I think LM358 Op Amp is really not appropriate to amplify the signals at all. I kept trying to boost the signal from 1v to 5v (somewhere around there} and it was not having it. As a matter of fact I could hardly get a signal out. Works great as a compare though. It is all I have on hand.

I tried to use a 2n2222 to amplify and really... transistors and I never get along. And I have a lot of different transistors.

What my goal is to get the 1v (really 1/2v ) video to nearly 5v for full activation of my Mosfet. No light what so ever from the led array with such low voltage.

Re: Handbook Sync Circuit

PostPosted: Mon Aug 06, 2018 3:18 am
by FlyMario
I guess I am really being silly to think Op Amps have the same function. Very embarrassing.

I have ordered CA3140 op amps from Jameco which should be here sometime this week I hope. I do realize that the CA3240 is a dual version of the CA3140 but it was easy to get.

Re: Handbook Sync Circuit

PostPosted: Mon Aug 06, 2018 8:32 pm
by Harry Dalek
I found trying the club circuit with different opamp's ..... or this older version i think a got a schematic off Albert
Worked out a sync seperator using part of the the club circuit but using an AN1358 , i was going to use the Mc1458 as in the circuit below but this ic worked much better ,nice video free clean sync pulse .\
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Picture 32005 (1).jpg
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Here's another circuit i got some where ....
Syncseparator and Leddriver.jpg

Re: Handbook Sync Circuit

PostPosted: Mon Aug 06, 2018 11:10 pm
by FlyMario
Damn Harry. According to Texas Instruments, my LM358 should be a replacement for the AN1358.

AN1358.jpg


That is frustrating. Not that I am sure that this is apples to apples. Who knows what perspective this sheet is looking from.

Did you drop in your An1358 into the circuit (hand drawn) in place of the MC1458 or where there modifications? That sync pulse is perfect.

Next and more importantly, is your real last name Dalek or is it in appreciation for the robots in Dr. Who?

Re: Handbook Sync Circuit

PostPosted: Tue Aug 07, 2018 12:50 am
by FlyMario
Another thing that puzzles me is the hand-drawn circuit looks almost identical to the circuit from the handbook... especially on the left side. However, the hand-drawn one shows 5v vs 12v. I would think that you would have to change the resistor values to go from 12v to 5v. That just may be my ignorance in analog circuitry. It is also interesting that no one uses a pot to adjust for the sync. Instead, they just apply a 180k resistor on the + and connect - to the signal.

I am sure they are all right... it is just confusing.

Re: Handbook Sync Circuit

PostPosted: Tue Aug 07, 2018 1:01 am
by FlyMario
Robonz wrote:
IC2 does amplify and adjust the black level. Seeing as you like digital and you are using an Arduino you could scrub all that and feed the video (IC2 pin 3) into the Arduino ADC pin. Convert that to PWM (just a couple of lines of code) and that could drive your mosfet with say 10 ohms on the gate.
It is quite possible you could extract the sync within the Arduino too using its built in analog comparator, or ADC. But get it going first.

Cheers
Keith


I really don't have the confidence that the Arduino ADC would keep up with the video signal. I think a person would have to build or obtain a faster ADC. It sounds like a fun experiment though. I keep thinking of different NBTV's I want to build. Perhaps I will take that approach on one of those. I like the idea of building one using a drum, though I am little concerned about the dots traveling in and out. Seems examples I have seen (on the tubes) work fine.