Diy Strobe for measuring turntable speed accuracy.

[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....

[Steerpike_jhb]

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 believe I know what you are saying, and I still maintain it isn't true.

Perhaps your technique of observation is different to mine: I do not use the strobe light beam/shadow edge as a reference point - my strobe-type lights have a very diffuse beam bondary anyway, so there is no 'edge' to use as a reference.
My eyes are very capable of determining if the circlar patterns of dots is stationary or rotating, with no such reference market. I'm not sure if that is a learned procedure or not.
If the rate of strobe-dot advancement or retardation is of the order of a few mm per hour, I couldn't see it, but that magnitde of error is too small to be relevant.

[Coffee Phil]

I just noticed this and had to comment. 45 RPM from 60 Hz mains is achievable. 3600 / 80 = 45. It is true that the highest synchronus speed for 50 Hz (3000 RPM) can not be divided by an integer to get 45 RPM.
33 1/3 on the other hand is a sweet number. 3600 / 108 = 33 1/3 and 3000 / 90 = 33 1/3.

Phil

a 45rpm strobe disc that is accurate under 50Hz lighting. The closest you can get is 45.112rpm

Fascinating!! So would you offset the crystal to get it accurate??

I have recently learned that most discs are actually cut at 45.11, and not 45.00 - because the cutting lathes were mostly driven from synchronous motors.
So the 'error' in the strobe disc turns out to not be an error at all, because you dont want 45.00.

Quartz turntables that do exactly 45.00 are apparently wrong.

will the disks work under a compact florescent light?
and are the little dots supposed look like they aren't moving, or should they be blurry?

Generally CFL lamps don't work - they don't flash at mains frequency, they have their own oscillators inside.
The blurriness of the dots depends on the 'quality' of the strobe waveform. My DIY version gives significantly less blurry dots than a mains-powered neon or LED lamp, because the current pulse to my LED is very short.

So how do i tell if my turntable is going at the right speed?

The strobe ring appears to stand still, as if it were not rotating at all.

[Alec124c41]

There are now LED Nite-Lites available, and cheap. They work perfectly for strobes.

Cheers,
Alec

[BirdMan]

I haven't reviewed all the posts but this is what I ended up using after other more expensive options and it works great! http://www.amazon.com/Professional-Laser-Photo-Tachometer-Measurements/dp/B000MMW0PY/ref=sr_1_4?ie=UTF8&s=automotive&qid=1292630988&sr=8-4

[MGuzzi]

For this or any other project which requires a printed circuit board (PCB), the best way of making one has a couple of drawbacks which are that it requires a laser printer, & you will not get away with tracks between closely-spaced pins.
1) Buy some ferric chloride crystals & follow the instructions for making a solution. Be careful because this stuff stains & will corrode certain materials.
2) Buy some PCB transfer film.
3) Draw the PCB layout in a computer program.
Then it is just a matter of following the instructions with the transfer film, which are, briefly:
print the layout onto the film with the laser printer; iron the film onto the PCB; carefully remove the film; etch the film in the ferric chloride solution.

This is a craft & will require a couple of practice runs. For example, the iron should be set to 90°C, but not many irons will thermostatically control themselves at this low a temperature, but increasing the temperature by quite lot seems to have no deleterious effect. For another example, cut the film around the layout with a good border, cut the PCB larger than this, tape the film to the PCB with the tape clear of the layout, put the PCB on a flat & heat-resistant surface, cover the film with a piece of paper, then put the iron on the paper & press for, say 30s, move the iron & press again for a few times. Do not move the iron while it as on the paper because the film must not be moved at all during this process. The press-move-repeat procedure is necessary because the heat distribution in the iron is not even.

If the layout cannot be achieved without tracks crossing there are two ways of
getting round this.
1 Replace offending tracks with cable links.
2 Use a two-sided board & some surplus component lead to join the sides.

Final notes
1 you will not get a professional job with this method.
2 I try to use tracks at least 0∙75mm thick.
3 Pens with oil-based inks are commonly found in stationery shops. This ink is etch-resistant, so suitable for touching-up the layout before etching, & cheaper than etch-resist pens.
MGuzzi