Diy Strobe for measuring turntable speed accuracy.

[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