[sdiy] Circle Machine prototype

Tue Aug 17 15:50:00 CEST 2010

Quintron is really good at playing his Drum Buddy, that's for sure.

T

Harry Bissell wrote:
> Another take on the circle machine...
>
> http://www.drumbuddy.com/
>
> (hey. it could work...)
>
> H^) harry  (yeah its an old thread...)
>
>
>
> ----- Original Message -----
> From: cheater cheater <cheater00 at gmail.com>
> To: David Brown <davebr at earthlink.net>
> Cc: Synth DIY <Synth-diy at dropmix.xs4all.nl>
> Sent: Tue, 17 Aug 2010 02:29:24 -0400 (EDT)
> Subject: Re: [sdiy] Circle Machine prototype
>
> On Mon, Aug 16, 2010 at 19:01, David Brown <davebr at earthlink.net> wrote:
>   
>> At 01:15 AM 8/16/2010, cheater cheater wrote:
>>     
>>> This is absolutely extremely cool. Can't wait to hear some sound demos.
>>>
>>> Several comments and questions:
>>>
>>> 1. you mention interference between the lamps. Try adding small
>>> matte-painted black walls between the separate lamps. Even better if
>>> you are able to connect them all together and move them in and out -
>>> then you can change how separate the lamps are.
>>>
>>> 2. different solution: take small plastic or sheet metal 'pipes' into
>>> which you insert the lamps. Make sure those pipes are at the top
>>> separated from the sensor by maybe 5 mm, and make sure the light
>>> source in the lamp is maybe 1-2 cm below the top of the pipe. Then you
>>> should get fairly good separation. Additionally you can move the lamps
>>> in and out to change the separation
>>>       
>> All those are good suggestions.  I think the light is reflecting off the
>> bottom vane.  I really don't need that vane as it just was a convenient
>> place to mount the photo resistor.  I should be able to remove it and just
>> let the photo resistor hang in free space.
>>     
>
> Hmm... I'm somehow having trouble picturing that. I thought the vane
> was supporting the lamps, not the photoresistor?
>
>   
>>  It's light enough in mass that
>> it won't be a problem.  The interference is pretty minimal but I won't mess
>> with it until I decide if I'm going to put a photo transistor there.  I will
>> have to remove the vane as there isn't physical clearance.
>>
>>     
>>> 3. you don't want too much separation, or the sensor will go dim
>>> between notes i guess :)
>>>       
>> The sensor does go dim between notes.  You can see those as the vertical
>> spikes on the last scope image.  The CdS sensor turns off faster than it
>> turns on.
>>     
>
> This sort of behavior can be fixed with an asymmetric low pass filter
> (i.e. one that has a different time constant for "rise" and "fall")
>
> On the other hand, those spikes could be part of "the sound" :)
>
>   
>>  This was actually one of my concerns with the original design.
>>  At slow speeds, there must have been a bunch of dead time if there was good
>> separation between notes.  I don't see how you could get a good blending.
>>  It was one of the reasons that I chose to use a stepper motor to step
>> between lamps.  I figured I wouldn't have to experiment with the best light
>> positioning to get a good transition.  Note that these spikes are only about
>> 60 mS wide so they are not that objectionable.  A bit of lag eliminated them
>> when I processed the output via analog.
>>
>>     
>>> 4. have you tried it with audio? I think that could sound like a
>>> really cool low-pass filter. But again, I'm not really sure what the
>>> settling time of such a sensor is :)
>>>       
>> I'm not really sure what you mean with audio?  All I'm doing is generating
>> an output of lamp brightess.  Certainly if I used LEDs I could modulate them
>> at audio rates.
>>     
>
> Yeah. Basically, get LEDs in there, and send the same audio to each
> led, or maybe two channels to alternating leds, and then just spin the
> photo sensor around.
>
>   
>>> 5. How have you made the arm? did you weld it yourself?
>>>       
>> The arm and the slip-disc are part of the Hammond vibrato scanner.  That's
>> why I chose to use it as a base.  It's a great slip ring.
>>     
>
> Where do you get one of those?
>
>   
>>> 7. Do you think diodes could work just as well?
>>>       
>> Diodes - you mean LEDs?  I thought of using those but I didn't want to build
>> the circuitry for dimming them.  Incandescent worked fine with rheostats.
>>
>>     
>>> 8. How fast does it go?
>>>       
>> I'm using half-steps so there are 200 per revolution.  I am clocking them at
>> 4 mS each, so I can do 1.25 revolutions per second.  I can clock at 2 mS but
>> there are some resonances so at specific frequencies I miss some steps.  I
>> haven't tried between 2 and 4 mS since I decided this was too fast for a
>> sequencer anyway.
>>     
>
> That's just about 192 BPM if you want quarter notes. Not so bad.
>
>   
>>> 9. Can it go backwards? Have you tried a 'random mode'? :)
>>>       
>> I have a direction pin so I can reverse the motor anytime.  That's another
>> reason I chose to use a stepper motor and a ComputerVoltageSource as the
>> controller.  I will most likely add a reverse, forward-back, and random
>> mode.  The problem with random mode is keeping a constant rate for the
>> sequence.  A 15 lamp rotation takes .71 seconds.  A single lamp rotation
>> takes 0.048 seconds.  You would want to incorporate the rotational time into
>> the per-step delay to hold a constant note rate.  This is another reason why
>> I chose to sample the output as there is a lot of dead time with multiple
>> lamp rotations.
>>     
>
> Sample the output?
>
>   
>>> 10. it's a bummer you can't get pitch perfect notes from it, but then
>>> again, maybe that makes it that much better for other uses :) That's
>>> not a reason to give up, much rather a reason to go on and extract
>>> that feature imo :) you've got something really cool on your hands :)
>>>       
>> I can get perfect notes from it.  I just can't tune it statically and then
>> rotate it.  I have to tune while rotating.  It's easy since I display the
>> note on the LCD.  At the faster rates where it detunes, it's too fast to use
>> for a sequencer as the notes just all mash together (to my ears).  Again, it
>> is repeatable so you just have to tune it at the rotational rate.  I think a
>> photo transistor would work much better.
>>     
>
> Would love to hear what the photo transistor works out like for you
>
> Good luck with your project :)
> D.
>
>   
>>     
>>> Cheers,
>>> D.
>>>
>>> On Mon, Aug 16, 2010 at 07:13, David Brown <davebr at earthlink.net> wrote:
>>>       
>>>> I'm sure it did.  I wasn't trying to build a faithful recreation - just
>>>> one
>>>> using lights and a spinner. It seemed like a stepper motor would be
>>>> easier
>>>> than a slow variable speed.  Besides, it gave me a chance to play with a
>>>> stepper motor.  - Dave
>>>>
>>>> At 09:54 PM 8/15/2010, David Griffith wrote:
>>>>         
>>>>> On Sun, 15 Aug 2010, David Brown wrote:
>>>>>
>>>>>           
>>>>>> I've been working on building a working model of Raymond Scott's
>>>>>> circle
>>>>>> machine.  I thought it would be fun to build something with motors and
>>>>>> lamps.
>>>>>>             
>>>>> [snip]
>>>>>
>>>>> I was under the impression that the Circle Machine didn't use a
>>>>> stepper,
>>>>> but instead a more mundane variable-speed motor and didn't have a skip
>>>>> feature.
>>>>> --
>>>>> David Griffith
>>>>> dgriffi at cs.csubak.edu
>>>>>           
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