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trippy rgb brain machinuino
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Re: trippy rgb brain machinuino

by mtbf0 on Sat Oct 18, 2008 12:44 am

here's an attempt to explain my code formatted as a lengthy comment.

finally started to think about adding color selection to the brain-wave table this morning while flying in to houston. going to the maker faire.

Code: Select all | TOGGLE FULL SIZE
// trippy rgb brain machine
//
// this software implements a sound and light machine, similar to mitch altman's brain
// machine as described in volume 10 of make: magazine.
//
// the functional differences between this implementation and mitch's are that this
// software attempts to synthesize a sine wave-like audio output and while the red leds
// blink at the intended entrainment frequencies green and blue leds fade in and out.
// admittedly the green and blue channels are more for the benefit of an observer than
// to enhance the entrainment function.  i, personally, do find that the visuals are
// enhanced by the blue and green lights.
//
// this software will run on an arduino or any mega168 running at either 8MHz or 16MHz
// with the following connections
//
//   PB1   - base frequency audio channel
//   PB2   - offset frequency audio channel
//   PC0,PC4   - red leds
//   PC1,PC2 - green leds
//   PC3,PC5 - blue leds
//
// it will also run on an attiny2313, specifically a modified adafruit industries
// minipov 3 kit clocked at either 8MHz or 16MHz.  the connections to the tiny2313
// should be
//
//   PB3   - base frequency audio channel
//   PB4   - offset frequency audio channel
//   PB0,PB5   - red leds
//   PB1,PB6   - green leds
//   PB2,PB7   - blue leds
//
// note that these connections differ from mitch's version most significantly in that
// one of the audio channels is moved from PB2 to PB4 so that it can be connected to
// OC1B output of timer 1.  the led outputs can be moved around freely by modifying
// symbols defined in the source code.  the green and blue outputs, as previously
// mentioned are primarily cosmetic and need not really be connected.  by defining
// the symbols RRED and LRED as PB0 and PB1 one can convert an existing slm with the
// only hardware modification being the movement of one audio channel.
//
// so, uh, how's it work?
//
// all of the outputs are generated in the timer 1 overflow interrupt service routine.
// the only things that happen in the main program are hardware initialization, setting
// up the brainwave sequence, then looping waiting for the sequence to end while
// periodically changing the brightness of the green and blue leds, and finally stopping
// timer 1, turning off all the outputs and putting the mcu to sleep.
//
// timer 1 overflows every 512 ticks of the mcu's clock.  at 8MHz this results in an
// interrupt frequency of 15625Hz, at 16MHz it's 31250Hz.  the advantage of running at
// 16MHz is that the audio pwm frequency will be well above the range of human hearing.
// at 8MHz one must rely on a low pass filter, cheap headphones and high frequency
// hearing loss.  (in 1970 i used to obliterate the rest of the world by getting home
// from school and lying on the floor with a speaker cabinet on either side of my head
// and band of gypsys cranked to about 7.5, so i'm halfway there.)
//
// anyway, at each timer interrupt a pulse is output on OC1A with a width proportional
// to the desired amplitude of the base frequency sine wave.  the offset frequency is
// output as a pulse on OC1B.  for each channel the integer part of a 24 bit fixed
// point, (8 bit integer, 16 bit fraction), phase accumulator is used as an index into
// a 256 byte table of 8 bit amplitudes.  for each entry, i, in the amplitude table,
// sinetab[i] = 127 + sin(i * pi / 128) * 127.
//
// for each frequency to be output a phase step is calculated at compile time.  this
// step is the change in phase for the frequency at each interrupt and is calculated
// by multiplying the frequency by the size of the sine wave table and dividing by
// the interrupt frequency.  step sizes for the offset frequencies are stored in a
// lookup table and the step size for the base frequency is stored in a separate
// variable. (declaring the base frequency to be a constant breaks the code, so don't
// try it.)
//
// the flash rate of the leds is controlled by comparing the phases of the offset and
// base waveforms.  the sign of the result of offset phase - base phase determines the
// state of the leds.
//
// color fading is done with seven bit pwm.  so the interrupt frequency of 15625Hz
// is divided by 128 for a pwm frequency of ~120Hz.  at every interrupt a counter is
// compared to 128.  when it reaches 128 it is reset to zero, the current values of
// all colors are copied to locations to be used for comparisons during the current
// pwm period, and all the leds are turned on.
//
// also, at every interrupt, the stored color values are compared to the counter and
// when they are equal the corresponding leds are turned off.  the counter is then
// incremented.
//
"i want to lead a dissipate existence, play scratchy records and enjoy my decline" - iggy pop, i need more
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mtbf0
 
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Re: trippy rgb brain machinuino

by mtbf0 on Mon Nov 24, 2008 9:31 am

think i found a wee little bug. i've been noticing occasional glitches in the audio and the other night i was perusing the timer1 section of the mega168 datasheet and noticed that in timer mode 8 the OCR1n registers are updated when TCNT1 hits zero. this renders my hurry up and update the registers at the top of the isr strategy pointless. or it would be pointless were it not actually a bug.

a wee little one.

haven't tested it yet, but it seems that the solution would be to move these lines

Code: Select all | TOGGLE FULL SIZE
//
// first output sample
//
    OCR1A = basesample;
    OCR1B = offsetsample;

from the beginning of the isr to just about anywhere else in the isr after the samples are calculated. when i've had time to test, i'll fix the post with the code.
"i want to lead a dissipate existence, play scratchy records and enjoy my decline" - iggy pop, i need more
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Re: trippy rgb brain machinuino

by mtbf0 on Sat Feb 14, 2009 9:10 am

finally did an arduino build of the brain machine. moved the leds from portc to port d.

this is an rbbb because it's what i had around and it's a little smaller than a boarduino.

top view. headphone jack is glued onto the power supply section of the board.
Image

low pass filter. connected at d9, d10.
Image

led connections. d2-d7.
Image
"i want to lead a dissipate existence, play scratchy records and enjoy my decline" - iggy pop, i need more
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Location: oakland ca

Re: trippy rgb brain machinuino

by GregW on Thu Apr 21, 2011 1:35 am

This is wicked! I have been thinking about getting the kit, but I really like the idea of using a 'duino and having more flexibility to add more programs or whatever. I was going to prototype this on an Uno, then downsize it to a Boarduino or similar...just had a couple of questions...I know this is pretty old...hoping you are still monitoring and able to respond...

Since the Uno uses a ATMega328, I modified the code to remove the splits for the ATMega168 and ATiny2313 and left the code for the 168...does that sound about right? It did compile after doing that, but I have yet to prototype the rest of the stuff to verify all works...

Also wondering if you have a more specific parts list...I can tell what goes where from you pictures and descriptions, but some of the components are hard for me to identify...I am still learning...

Lastly (for now)...since this is a couple o years old, are you still using this? Have you made any changes/improvements?

Thanks in advance!
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