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Old 1st Apr 2019, 3:21 pm   #61
TonyDuell
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Default Re: Turntable Stroboscope

I used 1/16th of the time because it was convenient for the ICs I used. There is nothing magical about that figure.

I assume you're taking the output from pin 3 of the 4060 (output Q14). Alas while you have Q13 and Q12 available, you don't have Q11. But you could get a 1/8th duty cycle by logically ANDing Q12, Q13 and Q14.

Get a 4081 IC (CD4081, etc). It's a 14 pin DIL package containing 4 AND gates each with 2 inputs. Connect :

Pin 7, 8, 9, 12, 13 to 0V (that also ties the inputs of 2 gates you're not using to ground).

Pin 14 to the +ve supply rail

Pin 1 to Q14 (pin 3 of the 4060)
Pin 2 to Q13 (pin 2 of the 4060)
Pin 6 to Q12 (pin 1 of the 4060)
Pin 3 to pin 5 (this couples the output of the first AND gate to one input of the second, thus making a 3 input AND gate).

Take the output from pin 4 of the 4081.

If you're using 74HC series ICs then the IC you want is the 74HC08. The pinout is different to the 4081. In that case :

0V to 7, 9, 10, 12, 13
Positive supply to 14
Q14 to 1
Q13 to 2
Q12 to 5
Link 3 to 4
Take the output from 6.

No calculations needed
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Old 1st Apr 2019, 3:28 pm   #62
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Default Re: Turntable Stroboscope

A 555 might be relatively easy, but the elegant way would be to do it in the counter logic.

You have a chain of flip-flops producing 300Hz, so four flip flops before the one whose output you're using will be at sixteen times your 300Hz. So one period of this ON followed by 15 periods OFF is what you want for your LED.

So we want a 4-bit binary counter in 74HC logic so let's look at 74HC161 about 0.30 isn't going to hurt the pocket and its in a 16pin through-hole package.

So now I need a datasheet.

Its pins are:

CEP Count Enable Parallel. Don't want this, we aren't loading data into it. tie to ground
CET Count Ensable Trickle input. Tie this to 5v we want to turn this function on
CP Clock pulse. yes we want this, feed in 4.8kHz from your divider chain to clock this counter.
Not(MR) Master reset, active low. Tie to 5v we don't want this active
Not(SR) Synchronous Reset. Tie to 5v, we don't want this reset either.
P0 to P3 We're not using the data inputs, tie them all to ground (never leave CMOS inputs floating)
Not(PE) we don't want to do parallel loading so tie to 5v to disable
Q0 to Q3 these are the flip flop outputs. We don't use them but must let them be free to move, so don't connect.
TC Terminal Count This is the one we want! It should pulse at 300Hz for us and give a pulse exactly 1/16th of a cycle.

So in pin numbers
1 Not(MR or SR) tie to 5v
2 CP this is out input. feed in 4.8kHz logic level signal.
3, 4, 5, 6 are P0-P3 so ground them.
7 is CEP tie to ground
8 is the ground pin, so you guessed it, ground it.
9 is Not(PE) so tie to 5v
10 is CET tie to 5v
11, 12, 13, 14 are the Q outputs, leave unconnected
15 is our output (Hooray!)
16 is the power supply. Tie to 5v and it's good practice to add a 0.1uF capacitor to ground.


THis might get you going for about 30p and that 0.1 ceramic decoupling capacitor.


David
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Old 1st Apr 2019, 3:30 pm   #63
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Default Re: Turntable Stroboscope

Slow me... posts crossed while typing at odd moments.

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Old 1st Apr 2019, 3:45 pm   #64
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Default Re: Turntable Stroboscope

Thanks guys for taking the time and effort to provide such detailed answers.

Good to see agreement over the use of the 74HC series ICs - just need to look closely at the different data sheets (74HC08, 74HC161) and clarify the pinouts

@David- elegance over easy every time.

Should keep me quiet for a while ... !
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Old 1st Apr 2019, 4:22 pm   #65
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Default Re: Turntable Stroboscope

I think it was at least one edition of 'The Art of Electronics' that said that using monostables was the mark of a bad designer as the timing could drift and in complicated systems really mess things up.

I wouldn't go as far as that. I do however try to avoid them wherever possible. I have been known to say 'you should only use monostables when you know enough to use them correctly'.

In this case a monostable _would_ be OK because the exact timing is not critical. It doesn't matter if the output is on 1/16th of the time or 1/10th or 1/20th. It will still be a useable stroboscope. On the other hand the purely digital solution, to take outputs from the counter chain and AND them, is probably simpler. It's certainly how I would have done it if I was designing such a device.
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Old 1st Apr 2019, 4:32 pm   #66
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Default Re: Turntable Stroboscope

In many, but not all cases, the use of a monostable has a hint of desperation about it.

Hard-bitten designers remember monostables as a thing that's often circled and bitten them! Aversion therapy.

What I haven't checked is that your divider has an output pin from the stage running at 4.8kHz That would be a nuisance.

That long chain divider is rather convenient, but I haven't used them much. Most of my counter logic in the past has been fast programmable counters as programmable frequency dividers for frequency synthesisers and for low noise, you want the whole thing synchronous so ripple counters are avoided.

Cheers
David


You're picking up a lot of experience at the moment. Horowitz and Hill "The art of electronics" is a good read and a great help when you're getting going. It's useful to have a copy around. I was able to repay H&H a little several years ago when Win Hill was having trouble trying to fast switch a high power RF amplifier into a peculiar load and he got steered my way for a bit of help.

David
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Old 1st Apr 2019, 4:43 pm   #67
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Default Re: Turntable Stroboscope

Thanks again guys - all really interesting background information.

I'll be sure to check out Horowitz and Hill "The art of electronics".

And then I made the mistake of Googling 74HC161 - how many variants of this are there and how do you choose?
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Old 1st Apr 2019, 4:50 pm   #68
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Default Re: Turntable Stroboscope

I will second the recomendation for 'The Art of Electronics'. I have all 3 editions on the bookshelves here.

As for the 74HC161, many manufacturers make it, so many different prefix letters (SN would be Texas Instruments, DM National Semiconductor, I think). And the suffix letters tend to indicate the package (DIL (through hole) or SOIC (surface mount), for example). But basically the IC is the same whichever one you choose.


Incidentally, have you tried feeding the 300Hz output of the 4060 into a transistor driver stage and an LED? It will be on half the time, but it may still be useable as a stroboscope. You may be doing all this work for no real benefit!
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Old 1st Apr 2019, 5:20 pm   #69
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Default Re: Turntable Stroboscope

A simple AND could be make from a series connected string of MOSFETs with the gates connected to the relevant outputs.
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Old 1st Apr 2019, 7:10 pm   #70
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Default Re: Turntable Stroboscope

Quote:
Originally Posted by TonyDuell View Post
Incidentally, have you tried feeding the 300Hz output of the 4060 into a transistor driver stage and an LED? It will be on half the time, but it may still be useable as a stroboscope. You may be doing all this work for no real benefit!
Thanks Tony - don't worry about the work, it keeps me busy and it's educational.

It will be interesting to compare and contrast the symmetrical square wave (50% duty cycle) with the asymmetrical square wave (6.25% duty cycle) when I get them working i.e. which one is best in giving a very clear stationary pattern on the strobe markings (I have a strobe disk for turntables).

And no real financial outlay either!

It's also allowed me to fire up my Topward Digital Function Generator, my ageing Farnell 30-4D oscilloscope and to get them properly connected. NOTE - still no responses to my Post #54 above.

Just realised that this will be Post #70 in this Thread - hopefully we are nearing a conclusion.

Just found 'The Art of Electronics' 3rd Edition on Amazon.co.uk - ouch!
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Old 1st Apr 2019, 7:20 pm   #71
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Default Re: Turntable Stroboscope

Ouch but still worth every penny new. Not too common second hand because people hang onto them. The differences between editions has been enough to persuade owners to buy the next one.

David
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Old 1st Apr 2019, 7:44 pm   #72
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Default Re: Turntable Stroboscope

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What I haven't checked is that your divider has an output pin from the stage running at 4.8kHz That would be a nuisance.
On Pin 15 I'm getting 4.7kHz-4.8kHz - seems like we are o.k.
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Old 1st Apr 2019, 9:46 pm   #73
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Default Re: Turntable Stroboscope

Brilliant!

Stand by for action! Anything can happen in the next half hour! (Apologies to Gerry Anderson)

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Old 3rd Apr 2019, 11:37 am   #74
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Default Re: Turntable Stroboscope

While I wait for the arrival of my 74HC161 order the next thing I need to look at is how to educate myself in transposing my breadboard layout to a circuit diagram to an actual circuit board.

This will be old hat for most of you guys but any help, hints or tips would be welcomed, including any pointers to "useful" online resources.

Tried looking at Eagle software but that looks like a steep learning curve ...!

Meantime I've got some strip board to try out.
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Old 7th Apr 2019, 12:23 pm   #75
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Default Re: Turntable Stroboscope

Thanks to some excellent off-line Tutoring from David G4EBT (again) I now appreciate that I need to start from the Logic or Functional diagrams and worry about the physical connections later?

My 74HC161 order has just arrived so hopefully this weekend I will have a fully working Breadboard prototype - now down to just three main components and a few caps??
  • QX14T50B4.915200B50TT - Oscillator, 4.9152 MHz
  • 74HC4060 - 14-stage binary ripple counter with oscillator
  • 74HC161 - Presettable synchronous 4-bit binary counter
  • 2 x 100nF ceramic capacitors
  • 1 x 0.1μF ceramic capacitor
Another issue I have with circuit drawing packages I've tried e.g. Eagle, is that I can never find the exact component from any of the Libraries!
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Old 9th Apr 2019, 11:18 am   #76
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Default Re: Turntable Stroboscope

Quote:
Originally Posted by Radio Wrangler View Post
Stand by for action! Anything can happen in the next half hour! (Apologies to Gerry Anderson)
Found some time at the weekend to wire up the 74HC161 making sure I carefully followed the instructions from TonyDuell and Radio Wrangler above.

As usual working hard to avoid a "painting by numbers" approach to ensure that I understand how components work and which connections to make before deploying anything!

Unfortunately the output from Pin 15 (TC - Terminal Count Output) of the 74HC161 is fluctuating wildly when connected to my Topward Digital Function Generator 8112.

Not sure where I've gone wrong but there are connections to almost every pin of the 74HC161 - maybe too many wires for a Breadboard prototype??
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Old 17th Apr 2019, 7:15 pm   #77
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Default Re: Turntable Stroboscope

Quote:
Originally Posted by TonyDuell View Post
I assume you're taking the output from pin 3 of the 4060 (output Q14). Alas while you have Q13 and Q12 available, you don't have Q11. But you could get a 1/8th duty cycle by logically ANDing Q12, Q13 and Q14.
Yes - I'm taking the output from Pin 3 of the 74HC4060 but this is Q13 and not Q14 as you infer.

The 74HC4060 doesn't have a Q10.

How does this affect the pin connections you kindly listed for the CD4081 and the 74HC08 in your Post #61 above.

Can't get any stability with the 74HC161 and unsure where to go next??
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Old 18th Apr 2019, 5:08 am   #78
TonyDuell
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Default Re: Turntable Stroboscope

I suspect the confusion on the output names simply comes from whether the output of the first stage of the counter (not brought out to a pin) is 'Q0' or 'Q1'.

Using the naming you are using, logically AND Q11, Q12 and Q13. That's pins 1,2,3 of the 74HC4060. The wiring I gave should be right.
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Old 18th Apr 2019, 9:22 am   #79
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Default Re: Turntable Stroboscope

Thanks Tony

My naming convention was simply based on the 74HC4060 data sheet - see below.

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Just to add further confusion (for me) the counter outputs appear to start at Q3 on Pin 7

No matter, we can all agree that Q11, Q12 and Q13 are pins 1,2,3 of the 74HC4060.
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Old 18th Apr 2019, 12:52 pm   #80
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Default Re: Turntable Stroboscope

Quote:
Originally Posted by DonaldStott View Post

NOTE - still no responses to my Post #54 above.
Just so you know you're not being ignored, the only observation I would make about that is that the vertical display looks rather odd, in that it makes the square wave look 'dovetail' shaped. Ordinarily, if the bandwidth of a scope is low, the 'risetime' will be slow and will be noticeable towards the limit of the scope's bandwidth. With a slow risetime the upward strokes of the display can slope forwards, (and the also the down strokes), but at such a low frequency of 300Hz, even on a scope with a low bandwidth the waveform should be square. I've annotated your picture in yellow to show what I mean.

I don't think it's due to the angle at which you took the picture (with your camera sloping downwards rather than square on to the screen) because the lines on the graticule look vertical. More like to be the adjustment of the scope or the way that the pic was taken than the strobe circuit because another cycle can't of course start before the preceding one is finished. If it does, you've invented a time machine not a strobe!

I've just taken a pic of a square wave on my own scope to show what it should look like.

Explanation of risetime: https://www.youtube.com/watch?v=eRA1Mx506fw

Hope that helps a bit, though it's no help in getting your strobe circuit to work as you wish it to, so good luck with that.
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