8mm Forum: I need your suggestions and criticals about a speed test instrument

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Posted by Renzo Dal Bo (Member # 5688) on July 04, 2017, 09:02 AM:

Hi everybody.
I need your expert help to improve my project. Any suggestions and criticals will be greatly appreciate.
For a long time, I have been searching a simple tool to quickly test the correct speed of a movie projector.
Unfortunately I did not find anything that met all my requests. In my mind it had to be simple to use, portable, battery supplied, without any projector disassembly and, above all, precise. So at the end I figured to build it myself taking advantage of the stroboscopic effect. First I realized a small working prototype, using an Arduino programmable board and a few other electronic components. The program I loaded on the board makes a power led flashing at specific frequencies, matching the common projector speeds. Due to the stroboscopic effect, when the projector runs at the exact speed, the main gear in the film path, illuminated by the intermittent light, appears to be motionless. In some projectors you can also act on the inside potentiometers to regulate the speed, if it was wrong, until the gear seems to stop itself. The tool I called "Strobo-Project" has only one main switch for power supply, ad two other push buttons. With the first push button you can select among five different speeds, showed by a corresponding turned on led, and in alternative stop the stroboscopic light. The second button turns on the stroboscopic light.
To test the accuracy of this instrument, I used two different projectors that can be synchronously controlled by a computer: an Elmo GS-1200 and a Braun Visacustic 2000. The final results were great and encouraging, despite the semplicity of the tool.
Now I am asking you about any improvement or changing you can suggest and think to be usefull.

Thank you all.
Renzo

[ October 06, 2017, 02:18 AM: Message edited by: Renzo Dal Bo ]

Posted by Phil Murat (Member # 5148) on July 06, 2017, 01:18 AM:

Hi Renzo,

Very interesting and brillant device you introduced there, ,I love the idea , congratulation !!!

I suggest you also to put an enter in the French Forum from LE TRANSFERT .
You"ll find Electronic Fans who like designing projectors modifications for Super 8 digitalizing.

Working on an ARDUINO Card is a very good idea as these cards are powerfull and very popular now.
"Cherry at top of cake" ARDUINO's are cheap.......

Did you use the "ARDUINO UNO" Model ?

Just a question, do you mean "Main gear" as the lower or upper sprocket (there are different diameters/Tooth numbers depending on models, so I assume different speeds considering a same frame rate)?
If Yes, what do you think about adding a "Tooth number" Select P/B , 2 P/B for increase and derease,(as an exemple, allowing 10 to 40 tooth setting) and joined to a small LED display showing Tooth number selected ?

Phil

[ July 06, 2017, 03:26 AM: Message edited by: Phil Murat ]

Posted by Steve Klare (Member # 12) on July 06, 2017, 09:12 AM:

I want to build a device that uses a phototransistor to detect the light pulses coming out the lens. Then it inputs them to a tachometer IC which puts out a voltage proportional to the frequency it measures.

LM2917 Tachometer IC

I could get fancy and build up a digital display to show the frame rate, but I decided instead to just have two jacks for a digital meter and have it read something like 2.40Vdc at 24 FPS, or maybe switch to the current scale and measure 24.0 mA at 24 FPS.

I'd want a separate jack so I could wire it into the 1/f switch on machines that have them.

I think I can calibrate this thing by aiming it at a fluorescent light fixture. If should read "20 FPS" at 60 Hz. I can borrow a meter with frequency measurement just as a sanity check. If they are running 63 Hz that day I don't all my pitches set high for the rest of my life!

It's a shame it's about 12th in line among my various projects! (Besides: the puddle I noticed developing on my basement floor the other day is a lot more threatening!)

How this is different from what you are doing is you get a calibrated indication of when your FPS is correct. I just get a calibrated measurement of what it's running. (-both good!)

Posted by Renzo Dal Bo (Member # 5688) on July 07, 2017, 08:07 AM:

Thank you Phil and Steve for your interest about my project.

@ Phil
I appreciate your offer to subscribe the french forum, unfortunately I don't speak french, but only a few english.
My instrument works for all the sprockets. It is not important which dimensions or teeth number they have. If the sprocket turns at the exact speed, every flash meets the next tooth in the same position than the previous one, so the sprocket appears to be stationary.
If the projector runs faster or slower you can regulate its electronic, if possible, until you see the sprocket apparently stops.
(When I was a child and was watching the Western Movies I didn't understand why the coach wheels turned in the opposite direction they should have had to go. Now I know it! It's the stroboscopic effect!)
Sometime ago a friend of mine asked me to modify his projector, that had only two fixed speeds (18/24 FPS). He wanted it worked to variable speed from 16 up to 25 FPS. I desoldered the internal 24 FPS pot and substituted it with an external potentiometer you can act on. To regulate the projector at the exact speed, I gave to my friend a Strobo-Project instrument.

I made the prototype of my project with an Arduino Uno board, but to realize the final instrument I used a smaller Arduino Mini Pro board. I agree with you these boards are very powerfull and cheap.

@ Steve
You are right Steve, to achieve something important it is necessary to dream it before. For sure my dreams are more down to earth and simpler than yours.
However to test my project I used a tool that makes your dream partially comes true. Look at the following photos.
For a few bucks, you can buy a tachometer for flying modellers .
They use it to test the propellers speed, so very similar to the shutters of our projectors. You have only to set the number of blades before (from 2 up to 9), and then you can read the propeller speed in RPM.
Just according to your requests it has "a phototransistor that detects the light pulses and inputs tachometer IC which puts out a voltage proportional to the frequency it measures" ... then displays on a digital LCD screen the speed, but unfortunately only in RPM.
I tested this tool also pointing it directly to the projector lens and it works very well but without the film in it. The shadows of the film frames make the misure less precise.
Reading what you wrote, I realized that I could input in my project the 20 FPS speed (expecially for US users with a 60Hz AC and 3 blades projectors).

Thank you so much again.

Renzo

[ July 07, 2017, 10:28 AM: Message edited by: Renzo Dal Bo ]

Posted by John Last (Member # 3414) on July 10, 2017, 10:50 AM:

I have made a frame reader which uses a light sensitive unit and a 9 volt battery plus on/off switch. You will need a meter which registers frequency. All you do is to offer the device up to the projector beam and the result should be 54 for a 3 bladed shutter. Its so simple and very accurate. The light sensitive device is from Maplin code: N5 7AY. Connect a 47K resistor in series with the diode and feed 9 volts across the two. Take a reading across the diode.

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