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Old 25th Apr 2019, 2:46 pm   #81
DonaldStott
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Default Re: Turntable Stroboscope

Quote:
Originally Posted by TonyDuell View Post
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.
Apologies my my start/stop Posts in this Thread - I find the time when I can!

I got to the stage where I think I understood connecting the output of Pin 15 (Q9) of the 74HC4060 (which is 4.8kHz) to Pin 2 (CP) of the 74HC161 which should deliver an asymmetric 300Hz from Pin 15 (TC) but I experienced severe instability problems with this set up.

So I decided to splash out another 30 pence and purchased a CD4081 to try TonyDuell's alternative approach. While I just about grasped the required pin connections detailed in Post #61 above I don't quite understand why I have three outputs from the 74HC4060 - Pin 1 (Q11), Pin 2 (Q12) and Pin 3 (Q13), to three inputs on the CD4081 - Pin 6, Pin 2 and Pin 1 respectively?

Labouring the point, sorry but I always like to know what I'm doing and why?
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Old 25th Apr 2019, 6:12 pm   #82
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Default Re: Turntable Stroboscope

OK, consider Q13. It's 'on' (high, logic 1, whatever you want to call it) for half the time. And off of the other half of the time.

Now consider Q12. It is also 'on' half the time, but it changes twice as fast as Q13. In fact Q13 will change when Q12 changes from 'on' to 'off'.

So Q12 and Q13 are 'on' together only a quarter of the time. Now if you combine those 2 signals with an AND gate the output of the AND gate is 'on' when both inputs are 'on'. That's a quarter of the time, and overall the signal repeats at the same speed as Q13.

Now bring Q11 into the circuit too. It changes twice as fast as Q12 (so 4 times as fast as Q13). Q11, Q12 and Q13 are 'on' together only 1/8 of the time. AND all 3 signals together and you get a signal that repeats at the same speed as Q13, but which is 'on' for 1/8th the time, off for the other 7/8ths of the time.

To AND the 3 signals you need an AND gate with 3 inputs. I simply told you to wire 2 2-input AND gates together to make such a gate.
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Old 25th Apr 2019, 7:15 pm   #83
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Default Re: Turntable Stroboscope

Thanks Tony - concise, eloquent and easy to follow.

Now all I need to do is connect it up properly!
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Old 27th Apr 2019, 5:39 pm   #84
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Default Re: Turntable Stroboscope

O.k. all wired up and double/triple checked my connections.

Something not quite right as I'm getting 8.5 - 8.6kHz on the Output from Pin 4 (2Y) of the CD4081 (actually a CD4081BE but I'm assuming the Pins are the same?)

Inputs on the CD4081 are as follows: -

Pin 1 (1A) from Pin 3 (Q13) of the 74HC4060 - 300Hz

Pin 2 (1B) from Pin 2 (Q12) of the 74HC4060 - 600Hz

Pin 6 (2B) from Pin 1 (Q11) of the 74HC4060 - 1,200Hz


Pin 3 (1Y) is connected to Pin 5 (2A) on the CD4081.


Pins 7 (Vss), 8 (3A), 9 (3B), 12 (4A) and 13 (4B) all go to -ve GRND.


Pin 14 (Vdd) goes to +ve 4.5V - only thing I haven't done is to connect a 100pF ceramic capacitor from this power supply Pin to ground?
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Old 27th Apr 2019, 5:52 pm   #85
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Default Re: Turntable Stroboscope

What do you get on pin 3 (or pin 5) of the 4081?

Do you have a 'scope? If so, what do the signals on pins 3 and 4 look like?
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Old 27th Apr 2019, 6:46 pm   #86
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Default Re: Turntable Stroboscope

Quote:
Originally Posted by DonaldStott View Post
O.k. all wired up and double/triple checked my connections.

Something not quite right as I'm getting 8.5 - 8.6kHz on the Output from Pin 4 (2Y) of the CD4081 (actually a CD4081BE but I'm assuming the Pins are the same?)
Re the 'BE' suffix:

A plain CD4081 is 'unbuffered'.

'B' simply means the IC has a buffered output. The pinouts are identical.

A 'buffered' CMOS device is one for which the output ON impedance is independent of any and all valid input logic conditions, both preceding and present. (I'm told!).

'E' means 'plastic encapsulated dual in-line package'.

An fuller explanation of buffered and unbuffered CMOS can be found here:

http://www.ti.com/lit/an/scha004/scha004.pdf

Hope that helps, albeit it doesn't answer they key questions.
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Old 27th Apr 2019, 8:29 pm   #87
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Default Re: Turntable Stroboscope

Quote:
Originally Posted by TonyDuell View Post
What do you get on pin 3 (or pin 5) of the 4081?

Do you have a 'scope? If so, what do the signals on pins 3 and 4 look like?
The readings on Pins 3 and 5 are widely fluctuating as well - makes no sense to me!

A complete mess on my ageing Farnell 30-4D oscilloscope - this needs a lot of urgent TLC so I don't trust what I'm seeing (not sharing it here!!!)

Quote:
Originally Posted by David G4EBT View Post

Re the 'BE' suffix:

A plain CD4081 is 'unbuffered'.

'B' simply means the IC has a buffered output. The pinouts are identical.
'E' means 'plastic encapsulated dual in-line package'.
Thanks David, although your link scared me - I'll need to find some time to read and digest.

Meantime ...

I think I'll need to PAUSE this Thread - I've taken up enough of your valuable time although it has been a very worthwhile educational journey, for me.

Made some great progress and actually managed to get something oscillating at a steady 300Hz - fell at the least hurdle though trying to generate an asymmetric square wave. So close ...

A huge thanks to everyone who contributed their knowledge, expertise, patience and perseverance, it really is appreciated.
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Old 4th May 2019, 11:18 am   #88
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Default Re: Turntable Stroboscope

Another reason why I have to PAUSE this Project.

WARNING: CONTAINS FLASHING IMAGES

https://youtu.be/Z8d1OIbbS-A

This should be a 300Hz asymmetric square wave!

Entertaining if nothing else!
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Old 5th May 2019, 7:25 pm   #89
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Default Re: Turntable Stroboscope

Well I braved looking at it.
If the timebase is set to 5mS/div (can't quite see the switch position) then that looks like just 50c/s hum pickup from floating input or missing ground somewhere.
Might also be a much slower signal but check for pickup first?
You previous scope pics (about post #54 from memory) looked fine for digital logic so no logical reason for this to be different - apart from miss-connection somewhere.
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Old 6th May 2019, 11:12 am   #90
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Default Re: Turntable Stroboscope

Thanks to buggies (George) for being brave (?) enough to look at my flashing scope display!

I was hoping that someone with experience would look at the display and recognise what was going on, or at least to suggest what might be wrong.

When I return to this Project in a few weeks (I've other things to attend to) I'll certainly check all my connections paying particular attention to any possible floating inputs or missing grounds.

Just to reiterate that at my level of experience (!) it's never clear if problems such as this are associated with the circuit design, poor/missing connections, breadboard contacts or faulty test equipment e.g. ageing oscilloscopes.

That's one of the many reasons why this Forum is, for me at least, such a valuable resource.
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Old 6th May 2019, 12:44 pm   #91
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Default Re: Turntable Stroboscope

That flicker-fest definitely looks as though there is a poor ground connection somewhere. Also, logic gates can misbehave if you have inputs floating (not tied to 0V or Vcc) or outputs tied to other outputs or fixed logic levels, and one gate wrongly wired can affect all the other gates on the same chip.

The first thing I think I'd do on getting back to this would be to prove continuity from the negative lead of the power supply smoothing capacitor to all my grounds; then check that there were no floating inputs or tied outputs on the logic ICs. It's important to probe right onto the IC pins themselves, to include every connection in the test: they are all suspect.

Good luck finding it! And try not to kick yourself too hard when you do
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Old 10th Jun 2019, 1:38 pm   #92
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Default Re: Turntable Stroboscope

Firstly it’s a big thanks to the Moderators for tolerating a Thread that has really nothing to do with Vintage Radio Repair and Restoration even though it’s in the Homebrew Equipment Section – hopefully others may find this useful?

Observant Forum Members will have noted that this Thread has been running for six months now - it has been stop/start with lots of periods of inactivity due to other more pressing matters. Before Posting anything on the Forum I did have a go at trying to reverse-engineer and recreate a commercial strobe that I had disassembled but very quickly encountered stability issues with my early attempts to "tame" the HEF4060BP – see early Posts above.

After various false starts and trips up several culs-de-sac the Project really took off and I embarked on a long and often arduous journey to reach a successful outcome. It's been really educational (for me) but probably a bit tedious for the Forum as I've not only discovered the joys of crystal oscillators, binary counter/dividers and square waves but I've also had cause to use my Topward function generator and ageing Farnell analogue oscilloscope. Add to that I've learned lots about voltage regulators and transistor driver stages. Most of this has only been possible with advice, guidance and encouragement from several Forum members which has proved invaluable - can't thank them enough.

In particular, a huge shout-out to David G4EBT, Radio Wrangler and Tony Duell.

A quick summary which of course doesn’t fully convey the much wailing and gnashing of teeth at various points: -

1. Started off looking to build a 300Hz strobe to check the rotation speed of my hi-fi turntable. Tried building a circuit based on the Product Data Sheet using a 4.9152 crystal and an HEF4060BP binary counter/divider but this proved too unstable and was not fit for purpose.

2. Enter Radio Wrangler with his suggestion to try the Qantek QX14T50B4.915200B50T crystal oscillator which is accurate to within 50 parts per million (0.005%). I also replaced the HEF4060BP with a 74HC4060 and these introduced tremendous stability to my circuit. I had a rock steady 300Hz on Pin3 (Q13) of the 74HC4060. I could have stopped there as I had a working strobe at 300Hz and which performed very well with my strobe disk - but I did appreciate that this was a symmetric square wave with a 50% duty cycle. From here it becomes mainly an educational project although I will return to this later. This is the waveform on my analogue 'scope coming from Pin 3 of the 74HC4060:-

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3. Now I needed to convert this to an asymmetric square wave with a duty cycle of 1/16th on and 15/16ths off - I did of course appreciate Tony Duell’s advice that there " ... is nothing magical about that figure" in Post #61 of my Thread but it seemed like a good figure to aim for? Radio Wrangler also provided guidance on the pin connections for various ICs to perform this conversion but I found that I could only get a stable waveform when using Tony Duell’s instructions for the 74HC08. This is the waveform on my analogue 'scope coming from Pin 6 of the 74HC08:-

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So far so good and looked promising to me. Once again I could have stopped there as I had a working strobe at 300Hz and the asymmetric waveform with the shorter on time did seem to give a much sharper focus to the lines on my strobe disk - but maybe that's just expectation bias or “audiofoolery” on my part! The LED was, however, a lot dimmer, so I needed to add a transistor stage – the ICs would need a 5V supply so some form of voltage regulation for that part of the circuit was required as power was coming from a PP3 9V battery.

4. David G4EBT is very much my Forum Mentor, Tutor, Guide, Educator and Instructor with seemingly endless patience and he was once again of enormous help at this stage and provided me with advice on building a voltage regulator module using an LM7805.

As a brief aside I have to mention that I did order some 7805 voltage regulators from a supplier who shall remain nameless and this was duly fitted into the circuit only to find excessive heat and some smoke from this component. After checking the text on the component (jeweller’s loupe is handy) I discovered that I had in fact been sent L7905CV voltage regulators which are different, especially in their pin configuration!!! The supplier was quick to replace these at no cost but the lesson to always read the small print cannot be overstated.

Later on David checked the total consumption of the strobe and a 78L05, rated at 100mA, was deemed more than adequate so was used as a replacement.

5. David G4EBT also sent me details of a standard transistor module using a 2N3904 and I added these two modules to my circuit. Wired up the transistor stage and checked the voltages to all the ICs and the feed to the LED etc. Double checked that I was still getting 300Hz from Pin 6 of the 74HC08 and that I was also getting 300Hz at the Base and Collector of the 2N3904. Amazingly it all seemed to work and this is the waveform on my analogue 'scope at the Base of the 2N3904 - as you can see it is set at 500mV/DIV so I reckoned we were getting just less than 1 Volt: -


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6. On the Collector of the 2N3904 I seemed to be getting the Gain I was expecting but the asymmetric square wave had been “inverted” somehow – this confused me for some time! The ‘scope was set at 2V/DIV so we had about 6.0V: -

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I had no idea what was going on due to my limited knowledge of such things but Tony Duell took the time to provide a detailed and eloquent explanation which I would summarise as follows: -

“That’s what I'd expect. It's a common emitter amplifier, so when the output of the 74HC08 goes high, it forward biases the base-emitter junction of the 2N3904. That junction, like just about any forward-biased silicon diode junction, will drop 0.7V or so.

Look at the transistor. When the output of the 74HC08 goes high, it sends base current into the 2N3904, forward biasing the base-emitter junction. This allows the collector-emitter current to pass, so the collector goes low in voltage. Think of the collector-emitter path in the transistor as a switch which turns on when the base current is applied. The voltage across a closed switch is small. So the collector is at a similar voltage to the emitter when the base current is flowing. So it goes low ANY common emitter (or common cathode) amplifier inverts the signal.

Now consider the LED and its series resistor. For the LED to emit light there must be a voltage across it. One side of the LED is at +9V or so. The other side goes to the collector of the transistor. So the LED is on when the collector is at a low voltage. The LED is on therefore when the output of the 74HC08 is high.”

As I said earlier this has been a very useful educational Project for myself and I had to read Tony Duell’s explanation several times to fully understand what was going on!

7. The circuit schematic went through many iterations, mainly suggestions and improvements by David G4EBT, including pencil and paper versions, Microsoft Paint versions and finally a version I struggled to complete using Eagle software - it almost got the better of me but my "stubborn" gene kicked in and I persevered. Of course I have to mention a basic connection that I had omitted and this error was picked up by David!!! But we finally ended up with a circuit that was to all intents and purposes complete - so at this point I had a Working Prototype, albeit on a couple of linked Breadboards. Hardly elegant but it worked!

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At this point it’s over to David G4EBT again who converted the circuit schematic into a PCB layout complete with tracks, holes and pins – quite amazing as I’m still battling with Eagle software to get to the stage of having a viable board. A couple of final tweaks have removed the reverse polarity diode as the board is powered by a PP3 9V battery and this helped shave some length off the PCB. David used the UV dry film negative photoresist method of making PCBs to produce a number of boards, a couple of which he sent to myself. Not to mention a package full of useful components required to complete my very own PCB – very generous.

(Continued in next Post)
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Old 10th Jun 2019, 1:42 pm   #93
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Continued ...

All components were soldered to the PCB and a suitable small ABS box was chosen to house the board, a switch, an LED chrome bezel and the PP3 battery.

This is what the finished product looks like: -

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Goodness knows what Forum Members will make of all this but I am reaching for the Chobham armour as I type this … !

Any Forum member that has contributed their valuable time, knowledge and expertise to this Thread, or even those who have taken the trouble to read it, are more than welcome to provide feedback, comments or corrections.

Some YouTube videos of the strobe and strobe disk in action may follow.

The good news (?) is that I’ve resumed work on the restoration of a Bush DAC90A which should keep me quiet for few weeks.
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Old 10th Jun 2019, 3:53 pm   #94
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Default Re: Turntable Stroboscope

The finished doodad is a useful gizmo for anyone with a turntable with a strobe ring on it and an appropriate number of bars.

You could do a magazine write-up

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Old 11th Jun 2019, 9:13 am   #95
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Default Re: Turntable Stroboscope

My input to this project has largely been to design a PCB and to suggest elements of the circuit to be added. Initially I didn't know if it was to be powered from say a 'wallwart' or a battery, so I included a reverse polarity protection diode, but the current consumed by the project was so low - just a few mA, and given that the strobe would only be used occasionally, and for a few minutes, a PP3 battery made more sense, and a TL05 regulator.

It's quite possible that given that only one ultrabright LED was to be used, and would only be 'on' for 1/16th of the time at 300Hz, that the output of the 74HC08 would have been adequate to drive the LED. However, given that a transistor driver only needed two resistors and a transistor, it added little complexity to include one. I claim no credit for that - it was 'lifted' from the circuit provided by Tony Duell in post #3 of this thread. Tony had used four LEDs in his strobe, and the relevant part of his circuit is enclosed. The LED and transistor are powered from the unregulated 9V line.

It may also have been that IC2, which converts the 300Hz square wave from a symmetrical to asymmetrical square wave could have been eliminated, making the circuit simpler still. However, since it wasn't known whether LEDs possess 'persistence' rather like a filament bulb, and hence, would not go instantly one and off at 300Hz, so would not give a solid 'flash' for each cycle, again, Tony Duell's idea of 1/16 'on' and 15/16ths off for each cycle was incorporated.

I played no part in the design or it's concept, in which - as has been stated, David ('Radio Wrangler') and Tony Duell had the major input.

Pic 1 shows Tony Duell's LED driver circuit from his design in post #3.
Pic 2 is the final 'Donald Stott' circuit of the 300Hx strobe.
Pic 3 is the component overlay and 'X-Ray' of the PCB I designed.
Pic 4 is the positive artwork for anyone who still uses pre-sensitised UV PCB laminate.
Pic 5 is the negative artwork for use with the negative UV dry film process.

The artwork in pic 5 can also be used for the laser printer 'toner transfer' iron-on technique , which obviated the need for a UV light box and developer. The artwork is shown in reverse because if printed as a UV mask, the ink side of the acetate must be next to the laminate, and if used for the laser toner transfer method, it must be printed as a mirror image or when ironed on, will result in a back to front PCB.

I don't use a PCB design package - I find them not easy to use, and not geared to homebrew techniques. I use 'Paint' for drawing circuits and creating PCB layouts and artwork.

I built one myself to check that it worked. (Initially it didn't as a link was missing from the circuit to ground pin 12 of IC1). Anyone looking closely at the PCB layout might wonder why there's a connection from pin 11 of IC1 to pin 6 of the crystal oscillator socket and then on to pin 7 of IC2, when the oscillator only uses pins 7, 8 & 14. I just used a spare pad on the oscillator DIL socket to get a track from pin 11 IC1 to pin 7 of IC2. (Rather like the spare pin used by Bush as an anchor point on the DAC90A audio valve socket!).

I've been pleased to have played a part in this project, which I knew from the outset would be pursued with dogged persistence to a successful conclusion. My own strobe is housed is a small ABS box 8cms x 6cms x 4cms deep.

Hope that's of interest and use.
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Old 11th Jun 2019, 9:58 am   #96
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Default Re: Turntable Stroboscope

I just gave a couple of gentle suggestions. I think Tony did the heavy lifting on the design, and the finished production version by G4EBT is rather professional. Stick your three names on it and bung it in PW!

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Old 11th Jun 2019, 7:11 pm   #97
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Default Re: Turntable Stroboscope

Quote:
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I just gave a couple of gentle suggestions. I think Tony did the heavy lifting on the design, and the finished production version by G4EBT is rather professional. Stick your three names on it and bung it in PW!

David
Thanks for the kind comments David.

As to PW, many years ago former Editor Rob Mannion changed the editorial policy to be exclusively about ham radio and that's the readership base it caters for. The eclectic range of practical constructional articles of yesteryear has long gone. ('Texan' amplifier, 'Wimborne' Music centre, Metal detectors, 'Robin' frequency counter etc etc). Since they discontinued Tony Nailor's excellent long-running series 'Doing it by Design' (which ran from 2004) and 'Technical for the Terrified' (ran from 2005), there's been little practical content of any kind, or so it seems to me.

The strobe is probably a bit too 'off topic' for the BVWS Bulletin too I think.

A few more pics below:

Pic 1: The 4.91520 Mhz square(ish!) wave output from the crystal oscillator to the input of the 74HC4060.
Pic 2: 300Hz square wave output from the 74HC4060.
Pic 3: The asymmetric output from the transistor driver to the LED.
Pic 4: Inside view of the prototype PCB, since modified and reduced in size as shown in my earlier post to remove the protection diode on the 9V input and to fit a 100mA 78L05 regulator rather than a 1 Amp 7805.
Pic 5: ready for the lid to go on the box.

The total consumption is only 8.5mA, due in part to the LED being on for only 6.25% of each cycle, and off for 93.75%, albeit to the human eye it appears to be a bright (ultra-bright!) continuous white light. Incidentally, I'm not sure what term would describe the current drawn by the LED - 'intermittent' DC, 'chopped' DC or what?!

I'll now need to print off a strobe disc to try out the strobe.
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Old 14th Jun 2019, 8:09 pm   #98
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Default Re: Turntable Stroboscope

Epilogue ?

With even more help and assistance from David G4EBT I managed to solder up the PCB he supplied with all the required components, fitted a switch and an LED while managing to squeeze everything, along with a PP3 battery, into an ABS box measuring 4 inches x 2¼ inches x 1 inch - a really tight fit!

All that shows is a switch and an LED - is that it I hear you say!!!!!!!

Various tests with a strobe disk had been carried out throughout the life of this project starting at the Breadboard stage and working through all the different versions so I thought I would Post something on YouTube just to prove that it does indeed work. The strobe disk that I have is a hand made job printed on paper from a template from the Vinyl Engine Forum and just stuck to a piece of cardboard meantime. Must devise something more elegant for this - any suggestions warmly welcomed!

So here is Test 1 showing the 300Hz strobe measuring the turntable speed at 33⅓ RPM - hopefully you will see the strobe bars on the outer ring remain stationary: -

https://youtu.be/wI7spkQzXO4

And here is Test 2 showing the 300Hz strobe measuring the turntable speed at 45 RPM - hopefully you will see the strobe bars on the inner ring remain stationary: -

https://youtu.be/Xl2VTXeNxZ8

Apologies for the shaky camera work!

It's been a long and often arduous journey to get here but a lot of time was taken to understand and control the duty cycle of the asymmetric square wave which has helped to improve the sharpness of the strobe bars pattern. This was achieved but at the cost of some light output and the transistor stage added towards the end really helped ameliorate that.

I've added a Post (#1090) to "The Thanks Thread" - credit where it's due.

https://www.vintage-radio.net/forum/...16#post1151816
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Old 14th Jun 2019, 10:17 pm   #99
Radio Wrangler
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Default Re: Turntable Stroboscope

Rob Mannion was very proud of the PW Robin frequency counter. As far as PW could gauge, he thought it was the constructional project which had been built by more people than any other. I'd have thought the Texan might have been in pole position, but maybe he didn't include that because it was long before his watch?

I have an enduring memory of Rob, a rather large chap with an artificial right hand, being helped up ladders and along narrow walkways on a tour of the Willis organ in George Dobbs' church. A nice guy.

David
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Old Today, 12:31 am   #100
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Default Re: Turntable Stroboscope

Regarding the perceived brightness of the LED, there's a phenomenon whereby a short duration flash is seen as being brighter than one of longer duration, even of the the same actual brightness. It's too long now since I was an optometry student, and I've gone off in altogether another direction since, so the details now elude me, but I'd expect a 208μs flash to be comfortably in the relevant range.
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