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Turntable strobe

Chris Riddell

Feb 12, 2015
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Hi Guys, I'm wanting to make a Zoetrope (http://en.wikipedia.org/wiki/Zoetrope) turntable strobe light that basically falls into these requirements:

  • 60 Rp/m turntable Motor
  • LED strobe light to flash each 30 degrees of the turntable
Would you guys do this with A 555 time chip? if so how would I sync it up to the midpoint on the 30 degree point of the turntable.

I can provide more info or pictures if needed

Thanks everybody :)
 

shrtrnd

Jan 15, 2010
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Both of my Pioneer turntables have the strobe. I'd find a schematic of the circuit used in a turntable thus equipped, and see what they did.
 

Gryd3

Jun 25, 2014
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Hi Guys, I'm wanting to make a Zoetrope (http://en.wikipedia.org/wiki/Zoetrope) turntable strobe light that basically falls into these requirements:

  • 60 Rp/m turntable Motor
  • LED strobe light to flash each 30 degrees of the turntable
Would you guys do this with A 555 time chip? if so how would I sync it up to the midpoint on the 30 degree point of the turntable.

I can provide more info or pictures if needed

Thanks everybody :)
Depending on what you find there, you could probably use an optical sensor or hall effect sensor to control when the strobe should go off. This would allow you to have a little flexibility without trying to maintain a specific RPM on the board.
 

KMoffett

Jan 21, 2009
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Not exactly 30° per flash, but there are strobe disks for turntables (free!) that are illuminated with a small neon lamp.
Google: turntable strobe disc

Ken
 

KMoffett

Jan 21, 2009
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Chris,
Sorry I missed the "Zoetrope". The 555 monostable could be used to give a fixed length light output. A couple of ways to sync the 12 pulses would be magnetic or optical. Twelve tiny magnets mounted around the axis of rotation, being detected by a Hall Effect sensor, that triggers a 555 , which drives you light source. Or a chopper wheel interrupting a photo-coupler, triggering the 555. Or a black/silver wheel activating a reflective photo coupler, that triggers the 555.

Ken
 

Chris Riddell

Feb 12, 2015
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Sounds good ken, would you know of a good circuit diagram to show this? i'm fairly new to electronics...
 

KMoffett

Jan 21, 2009
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Let's work backwards. What is the light source that you are intending to use?

Ken
 

Chris Riddell

Feb 12, 2015
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Thanks Ken I'll post up a better description of what I'm after doing when I get home tonight.
 

Chris Riddell

Feb 12, 2015
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Hi Ken,

I am going to light the turntable with a series of LEDs like this http://www.instructables.com/id/DIY-portable-LED-strobe/

And there are 12 frames of animation per revolution of the turntable so I need the strobe to go off 12 times in an interval of 30 degrees, I know I could probably make a 555 timer strobe and set the value with a POT but I fear it could get out of sync, so perhaps a LED or Magnet could start/reset the sequence?

The whole thing needs to be smooth without any jumps or it'll break the illusion of the animation.

Perhaps a 555 isn't the route I need to go with?
 

KMoffett

Jan 21, 2009
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OK, they're using the 555 in the astable oscillator mode. It will work in the short term, but as the motor speed varies it will not track. If the 555 is used in the monostable mode it will output a single, short light pulse when it is triggered buy a magnet or optical sensor at 30° intervals, no matter how the motor changes. The electronics are pretty straight forward. But, which sensor system is easiest to implement depends on the mechanics of your Zoetrope. For the optical Google: images optical chopper wheel.

Ken
 

Chris Riddell

Feb 12, 2015
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Sounds awesome Ken thanks you :) any idea to how I can find a good circuit diagram to do this? sorry I'm very new to electronics. Im a technical computer artist/programmer so I understand theory quite a lot.

So as I understand I will put a magnet per frame on the turntable I make, make a monostable 555 controller for my led block I make and then use a Hall effect sensor for the trigger?
 

KMoffett

Jan 21, 2009
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Yup. But I would never arrange the LEDs in the series/parallel configuration that the Instructables show. :eek: It may have worked for him, but it is a "bad" design. LEDs are current-operated devices and should not be placed in parallel. Attached is a 555 monostable version of the Instructables, with options for magnetic or optical triggering. And...a "proper" LED array configuration. I only used 30 LEDs, but this can be expand by just adding more strings of the resistor and 3-LEDs in parallel. Each string draws 100mA at 12V, so the ten strings shown draw 1A. If you increase number of LED strings, you would need to increase the 12V power source current proportionately.

Ken

555 Monostable Strobe LEDs.gif
Schematic corrected!
 
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Chris Riddell

Feb 12, 2015
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Thank you ever so much Ken that's amazing! I will try and get this made soon. Thanks and have a fantastic weekend :)
 

Chris Riddell

Feb 12, 2015
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Would it be a 27 ohm resistor? Also I can't seem to source a IRF244N would you know what an alternative would be?
 

KMoffett

Jan 21, 2009
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In the schematic, above the LED array, R=100Ω/1/4W. Your LEDs are rated at 50mA (continuous?). But since we are only driving them with very brief pulses I upped that to 100mA.

OOPS! That's wrong. (12V-3.5V-3.5V-3.5V)/100mA=15Ω and 1.5V*0.1mA=0.15W so 1/4W. R=15Ω-1/4W
I must not have had enough coffee. ;)
27 Ω- 1/4W would also work for ~50mA
An IRF510 should work and is readily available.

Ken
 
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