Diy Strobe for measuring turntable speed accuracy.

by **Steerpike_jhb** » 29 Jul 2010 19:45

safe1 wrote:one last (i hope) question:
what should be connected there? :

Nothing, or just solder pins (cut off component leads). Those two pads are test points for a frequency counter or oscilloscope.

by **irwan_su** » 30 Jul 2010 01:10

Since I don't understand how to read the scheme and soldering, I just bought this

Speed measurement result for my Thorens TD125

by **safe1** » 30 Jul 2010 03:39

irwan_su,

does that need a reflective mark on the platter side?

by **irwan_su** » 03 Aug 2010 00:57

Yes it need a reflective mark on the platter side, like in this picture .

by **1200y3** » 04 Aug 2010 14:06

Show me some evidence that a power company has poorer line frequency than we can do ourself. If speed inaccuracies are a concern then a test record with 400HZ and 500hz tones are measured up against WWV (NIST) and a frequency counter, which are very cheap for the accuracy today.

How do you know that strobe dots are accurate then?

A portable battery operated strobe is great for the convenience, but how would you know if it slips off frequency?

And if you are thinking about a strobe because you simply want a clearer display then a plug in LED nightlight works excellent. For $2 you're in business. But if you use a neon lamp with a rectifier, you won't get fooled, because all bands are visible, but in motion, when one band is locked.

by **JaS** » 04 Aug 2010 14:57

1200y3 wrote:Show me some evidence that a power company has poorer line frequency than we can do ourself.

I can't do that but I can show that mains frequency here in the UK drifts with demand so it's not ideal for accurate speed measurement. I'm guessing other countries are the same (and some are probably worse).

http://www.dynamicdemand.co.uk/grid.htm

Of course if you aren't bothered about trying to find a more accurate method to check speed then this thread probably isn't for you.

Regards,
JaS

by **1200y3** » 04 Aug 2010 15:27

I am sorry, I neglected the differences in line frequency and the loads on it. There is a huge difference. I believe the province I live in has a very small population for land mass.

Just look up the area of Saskatchewan to its population, compared with all of EU.

by **Steerpike_jhb** » 04 Aug 2010 16:54

1200y3 wrote:Show me some evidence that a power company has poorer line frequency than we can do ourself.

Have you got a dual trace oscilloscope? Hook one trace to a quartz oscillator, and the other to the AC mains & watch the 2 sinewaves.

Mains frequency is deliberately skewed too. Under high load conditions, it drops. Under light load conditions, they up the frequency at the power station to make up for lost cycles - so the total number of cycles over a 24h period is always constant.

How do you know that strobe dots are accurate then?

Just count them! What may vary is the spacing, but minor misregistration when printing or machining the dots doesn't result in any error in frequency checking when using the strobe - it may make exact evaluation of flutter imprecise, but not rotational frequency.

A portable battery operated strobe is great for the convenience, but how would you know if it slips off frequency?

Quartz crystals don't. It just doesn't happen.

then a plug in LED nightlight works excellent. For $2 you're in business. But if you use a neon lamp with a rectifier, you won't get fooled, because all bands are visible, but in motion, when one band is locked.

If your motor is synchronous, you're stuck. The strobe is affected by the same errorr that makes the platter speed erroneous. So the result is zro visible error regardless of how large the error is - it could be +/- 100% and amains driven strobe would show it as perfectly aurate.

by **Werner** » 04 Aug 2010 19:46

"Quartz crystals don't. It just doesn't happen. "

I'm sorry, but I have a quartz/LED strobe, and just before the battery drains, the frequency goes a bit slow while the luminance seems OK.

by **Steerpike_jhb** » 04 Aug 2010 23:40

Werner wrote:I'm sorry, but I have a quartz/LED strobe, and just before the battery drains, the frequency goes a bit slow while the luminance seems OK.

I might be pushing the 'technical' aspect too hard, but strictly speaking, the circuit is failing to operate, it's not really a drift or inaccuracy problem. Correct its power supply fault, and its accuracy will be bang-on-accurate.

That's a bit like saying if your car runs out of gas, then it's "failing to achieve the acceleration claimed by the manufacturer"

Egad! My previous post is so full of typing errors. I must not post in a hurry!

by **Werner** » 05 Aug 2010 07:10

Well no, it was not obviously failing, so it led to erroneous speed measurements. Only a short while later reduced the LED's brightness and then it became clear what had happened.

by **safe1** » 05 Aug 2010 15:23

...and what is your point Werner?

That an accurate hand-held DC strobe light can't be built?

I'm just asking because i finished making steerpike's strobe light
few days ago and i works fine to me.

If you're afraid that when the battery power goes down it may give inaccurate readings, you can always replace the 9V battery with
a 9V DC power source. No?

Other than that, i find steepike's contribution invaluable when similar
strobe lights out there cost from about $60 to well above $150.

by **1200y3** » 05 Aug 2010 15:52

A dual 9v battery supply with a simple voltage regulator circuit improves the stability of most low voltage IC circuits. It's just a simple addition of a small transistor (an IC that looks like a transistor), tiny cap and resistor.

Anyone with enough experience with ICs and a 9 v battery will see this as the battery gets weak.

by **Werner** » 05 Aug 2010 17:04

safe1 wrote:That an accurate hand-held DC strobe light can't be built?

No. Just the simple fact that I have had one deviate from true frequency, due to a sagging battery, and this going unnoticed for a while, with all associated risks.