Re: Turntable Stroboscope
 

Are all the prefixes and suffixes just designed to confuse someone like me??

I think this looks o.k. to me: -

https://uk.farnell.com/texas-instrum...07?st=CD4060BE

Re: Turntable Stroboscope
 

That would be fine.

The first two letters are of no significance - they just denote the maker.

For example, CD is RCA, MC is Motorola, SN is Texas Instruments.

Note however that while those from Farnell are cheap, they're US stock so you get caught with £15.95 delivery charge.

Re: Turntable Stroboscope
 

Noted David, thanks.

Managed to find some on eBay from a UK supplier.

Re: Turntable Stroboscope
 

I've replaced the 4060 along with the 4.9152 MHz crystal just in case that was fried as well.

Rewired my Breadboard circuit with shorter leads and paying much more attention to detail (thanks Trigon) - everything oscillating nicely but not quite the stability I need.

Still some fluctuation (+ - 10-20 Hz) which I assume could be being caused by some back voltage?

Would some judiciously placed diodes help in this instance?

I'm just doing this for my own education and interest (or stubbornness!) as I've also acquired the QX14T50B4.915200B50TT to try out as recommended by Radio Wrangler.

Re: Turntable Stroboscope
 

I had a go at making a strobe but in a senior moment designed it to give 50 or 60Hz square wave to drive a high brightness LED. When it did not work against a standard stroboscope disc the light came on in my head and I converted it to 100 or 120 Hz operation. :D
It was easy to do by re-selecting the LOAD inputs of the CD40103.
So the 4060 produces 2400Hz from the 2.4576MHz xtal, trimmed to give correct frequency. It runs from its own regulated 5V supply, the rest of the circuit uses the full 9V. Though it works fine, I failed to realise, as suggested in earlier post, that a shorter pulse would improve viewing on a strobe disc. That would probably make the CD4013 unnecessary and the 40103 could then be made to provide the 100/120Hz by making it divide by 24, (actual required load word 00010111 (23) and divide by 20, (actual required load word 00010011 (19) so only load bit J2 needs switching. Not tried that as the present illumination is OK for me. :D

Re: Turntable Stroboscope
 

After many false starts and abandoned trials I finally have a circuit oscillating at exactly 300 Hz - apologies for the shaky camera work: -

https://www.youtube.com/watch?v=7doS...ature=youtu.be

Thanks to Radio Wrangler (David) who encouraged me down the route of using a Qantek QX14T50B4.915200B50TT oscillator.

Next step is to replace the HEF4060B with a 74HC4060.

After that it's looking at the output waveform on my 'scope and what I need in the circuit to drive an LED i.e. get my head round Tony Duell's comments in Post #6 above and all that stuff to do with "persistence"!

A general thanks to Forum members for their ongoing support ...

Re: Turntable Stroboscope
 

"After that it's looking at the output waveform on my 'scope ... " - now there's a phrase that's easy to type but proving extremely challenging with my ageing Farnell 30-4D oscilloscope (rebadged Scopex 4D25 or Racal 9386 ?)

Any help would be appreciated ...

Re: Turntable Stroboscope
 

As to 'persistence' Tony Duel made a good point in post #6 regarding his (quite involved) circuit. Namely:

"The LEDs are on for 1/16th of the time. A short flash (rather than 50:50 on/off ratio) gives a clearer 'still' pattern of the strobe disk".

With an asymmetrical square wave, the LED is on for a shorter time than with a symmetrical square wave, so the flash period of the LED is shorter. Hence, if the LED has some ‘persistence’ rather than go straight off, it fades till the next ‘on’ period, so at 300 HZ might not seem to go off at all but may appear both to the naked eye and the strobe disc as a continuous light. To cite Tony's circuit, the LED would be on for only 6.25% of each cycle, and off for 92.75% so the flash would be more clearly defined, rather than a symmetrical square wave which would be high for 50% of each cycle, and low for 50%.

We know that LEDs quite unlike incandescent light bulbs in which a filament glows and take time to heat up and cool down. What isn't known, is to what extent say ultra-bright low current LEDs have 'persistence', and the only way of knowing that is to try one on a normal 50:50 square wave 300Hz signal.

As to your scope, you've said that you now have a stable 300Hz signal from your oscillator circuit, so if you feed that into the 'Y' input of your scope it should have do difficulty in displaying that to enable you to see the waveform, and the voltage. Don't know if the output of the oscillator would be high enough voltage to drive a low current ultra bright LED directly. Again, the only way of knowing is to try one.

What we do know for certain, is your own undoubted 'persistence' as amply demonstrated both with this project, and with the 'basket case' Bush AC91, which you persevered with until it behaved itself, long after many would have become disheartened and thrown in the towel!

Good luck with the project.

Hope that helps a bit.

Re: Turntable Stroboscope
 

Thanks David G4EBT for your ongoing encouragement, support and off-line mentoring - it really helps.

My Farnell oscilloscope (a rebadged Scopex 4D25?) was bought from another Forum member a few years ago but has never seen active service until now. It's fairly tatty and some of the front panel text was missing and replaced manually!! Of course I'd rather be using an oscilloscope than having to repair this one!

A few of the knobs feel as if they are slipping and I'm not sure if the trigger is working correctly? I'll be happier when I can see a waveform on the screen.

I'm quite pleased though that even at my age I'm still able to ask "daft boy" questions like "Where is the 'Y' input on my 'scope" - see image below.

Attachment 180180

Re: Turntable Stroboscope
 

Y is vertical axis, X is horizontal axis.

So Y in = Vertical, use A Vertical (BNC socket) and trigger from that channel.

Lawrence.

Re: Turntable Stroboscope
 

There's a useful general guide to using 'scopes at the Eddystone User Group site which you might find useful.

You can download it here - you don't need to be an E. U. Group member:

http://eddystoneusergroup.org.uk/Res...0Servicing.pdf

Re: Turntable Stroboscope
 

The only LEDs with significant persistence are the white ones with a phosphor, all others respond very (sub uS) quickly.

Re: Turntable Stroboscope
 

I did not try to measure the persistance of the white LEDs I used in my strobe project. What I do know is that with the circuit I gave I get a _very_ clear stationary pattern on the strobe markings of the spindle of an old floppy disk drive (which is what I originally made it for). Even if the persistance of the LED keeps it on for longer than 1/16th of the time it still goes off for sufficiently long to work.

Re: Turntable Stroboscope
 

With the help of Forum members I've finally got my circuit oscillating at a steady 300Hz - time to start looking at the waveform on my scope?

Looking first at the Qantek oscillator with the HEF4060B I'm getting this: -

Attachment 180546

Switching out the HEF4060B for a 74HC4060 I'm getting this: -

Attachment 180547

Not sure how to interpret these as the HEF4060B looks "cleaner" than the 74HC4060 - not what I expected?

Or to what extent are these displays down to my my ageing Farnell 30-4D oscilloscope. ???

Feedback would be welcomed. :)

Re: Turntable Stroboscope
 

So now that I have what looks to me like a symmetric square wave displaying on my oscilloscope, what circuitry do I need to add to convert that to an asymmetric square wave?

"The LEDs are on for 1/16th of the time. A short flash (rather than 50:50 on/off ratio) gives a clearer 'still' pattern of the strobe disk".

Really enjoying the educational aspects of this Thread - thanks to everyone for their ongoing support.

Re: Turntable Stroboscope
 

A 555 timer in monostable mode. Drive trigger pin with your wave.

Re: Turntable Stroboscope
 

Logic AND the 300Hz and the four faster ones. At this speed diodes would suffice.

Re: Turntable Stroboscope
 

Yes, that too. Or NOR suitable pins with transistors.

Re: Turntable Stroboscope
 

Thanks to Mike and Merlin for suggested ways forward.

As the 555 timer is cheap'n'cheerful with lots of information online about monostable mode I'm off to read up on this stuff and see how far I can get on my own!

Re: Turntable Stroboscope
 

I've taken a step back as I was getting my frequencies, duty cycles, asserted signals and other concepts confused - so bear with me but please BUZZ when you see an incorrect step!

We currently have a 300 Hz symmetrical square wave so the duty cycle is 50%

At 300 Hz the time interval is given by 1/300 = 0.003333 seconds = 3333 microseconds.

So within this 3333μs period we have 1666.5μs of asserted signal, followed by 1666.5μs of deasserted signal i.e. 50% duty cycle.

Ideally we want the LED to be on 1/16th of the time which is 3333μs divided by 16 (or multiplied by 0.0625) = 208.3125μs.

6.25% duty cycle and an asymmetric square wave ??

So far, so good ...?

How do we then calculate the circuity needed e.g. resistors and capacitors, to produce the necessary input for a 5555 monostable mode circuit??