Diy Strobe for measuring turntable speed accuracy.

[1200y3]

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.

[Steerpike_jhb]

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.

[Werner]

"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.

[Steerpike_jhb]

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!

[Werner]

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.

[safe1]

...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.

[1200y3]

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.

[Werner]

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.

[safe1]

Well i will leave this debate to the experts of electronic circuits since i'm not one of them...

...but for the reasons i described in my previous post i'm grateful of this strobe light contribution...

Nevertheless, in my opinion, there is no point to analyze a handheld strobe light accuracy since its usability is affected by one more VERY important factor:

the "rock steady" hand that holds it against the strobe disc!
And i have trouble to keep my hand rock steady for the whole amount of time i'd need to adjust the speed totally spot-on.

If we need to very-fine tune the r.p.m.s of a turntable we need to have a strobe light constantly steady which can be achieved only if the strobe light is fixed on a certain position of the TT.

Other than this can't guarantee totally accurate result. It's very dependable on the steady or unsteady hand that holds the strobe light...

(at this point i feel that most of nowadays TT manufacturers
are doing a bad work by setting aside the inclusion of a decent strobe light
on their decks).

[Steerpike_jhb]

Nevertheless, in my opinion, there is no point to analyze a handheld strobe light accuracy since its usability is affected by one more VERY important factor:
the "rock steady" hand that holds it against the strobe disc!

Not true. The strobe does not need to be held still or steady at all.

(Unless your hand motions are so severe that they approach the speed of light [298000km per second])

[1200y3]

It can't be too difficult to set the lamp stationary on the turntable anyway. What may be a concern is vertigo/hypnosis that can occur when the WHOLE strobe disc is illumuminated and you have a disc with 2 speeds and 2 +/-speed bands (10 bands /disc) and you use a rectified strobe. It is less distracting if only 4 or so dots show at one time.

[dmaster]

I would like to build this thing in my tt.
Only the voltage is 18DC, since the ve_diy_storobe.pdf says it is for 9V-14V I'm afraid this won't work for long if i mount it without any modification.
Is putting a resistor in series of the + line to the strobe a good idea? And what value should I use then?
And would it effect the 18V to the motor?

[Steerpike_jhb]

I would like to build this thing in my tt.
Only the voltage is 18DC, since the ve_diy_storobe.pdf says it is for 9V-14V I'm afraid this won't work for long if i mount it without any modification.
Is putting a resistor in series of the + line to the strobe a good idea? And what value should I use then?
And would it effect the 18V to the motor?

The CMOS chips used in the circuit have an absolute maximum voltage rating of 15V, so 18V is too high. A better way than a resistor to drop the voltage is with a Zener diode, say 5.6V or 6.8V rated at 1Watt, (or two 3.3V or 2.7V in series, if they are easier to get).
Not that the zener diode must be connected the 'wrong' way around - CATHODE (stripe/line) to the battery +, ANODE to the + supply rail of the circuit board.

But just as easy would be an LM7812 three-pin regulator. Easy to use & cheap.

It should not affect the motor at all, since the current used is low. Just don't take the voltage DIRECTLY from the motor terminals, as the turntable may have a control circuit preceeding that. Find the power supply DC output.

[safe1]

Nevertheless, in my opinion, there is no point to analyze a handheld strobe light accuracy since its usability is affected by one more VERY important factor:
the "rock steady" hand that holds it against the strobe disc!

Not true. The strobe does not need to be held still or steady at all.

(Unless your hand motions are so severe that they approach the speed of light [298000km per second])

Hi Steerpike,

I didn't mean that.

What i meant is that in order to observe the strobe disc lines activity (and decide if they move CW or CCW), the reference light that glows on them should be steady.

It's the only way to have a reference spot and observe the strobe disc line next to it.

If the hand that holds the strobo light trembles or even moves a few mm (or cm) left or right then you lose your observation reference spot.

I don't know if my English express my thoughts well on this matter....