Rare Angles was an Audio Visual  art piece for Burning Man 2007.

Consisting of a 4m tall Bass Cannon, and a  3m diameter array of spinning LED's.

I wanted to have an umbrella of lights that would change in time with music fed into the bass cannon.

To do this I used a Picaxe28x microcontroller, 10 LM4970 chips and 30 RGB LEDs all connected on an array spinning around on top of the Bass Cannon.

When the audio is bass heavy the led's shine blue, mid range gives green, and high frequency creates a red light as well as everything in between.

I could also change each of the led's to any of 7 pre defined colours, as each of the LM4970 chips are individually addressable on the i2c bus. 

The array spun arround driven by a pancake motor. I didn't expect the wind to stall the motor, but it did, and within a few days had burnt out. The motor was also under powered so I was not able to get anywhere near the streaking of light I wanted to acheive.

But anyway this is how I did it.

Audio is fed in via line inputs to an FM transmitter or wireless Microphone		Audio passes through a lowpass filter to remove frequencies over 50hz
The audio is processed by one of 10 LM4970 chips. The CPU also enables the onboard fm radio to receive audio signals.		A simple voltage sensitive switch is used to detect beats and send a pulse into the CPU. This pulse is used to trigger different colour modes in the LM4970 chips
The LM4970 chips 3 Pulse Width Modulated outputs drive current amplifiers to then drive the LEDs		The 300w Keiga panel amp drives the sub
There are 3 arms on the array each with 10 LEDs. 1 LM4970 chip drives one band of LEDs		The sub is located inside the bass cannon.

 The main controller board held the picaxe, 10 LM4970 sound PWM chips, a couple of shift registers, a UHF remote control receiver and some extra output terminals to switch the FM receiver (which received the audio input) on and off. 

The shift registers were required to address the LM4970 chips as they only had 2 possible address' each. I used the shift registers to switch the address pin either high or low on each chip. By shifting in the chips address serially, then pusling the shift out pin on the chip the address is revealed on the output pins. By connecting these pins to the address pins of the LM4970 chips I could address them individually or in groups.

 The other main PCB was the LED driver board. This pcb held 30 transistors. The maximum output from each of the 3 PWM ports on the LM4970 chips is 42mA. I boosted this to 120mA using the transistors. Each transistor drives 3 leds. 30 LED's x 3 colours each = 90. So each transistor drove 3 led elements. Next time I'll use DIL a transistor package.

Also spinning inside the array was a small PSU board that I won't show here. Just a simple regulator with a pair of large capacitors. At full load the LED's drew  3.6 amps.

The PCBs all screwed onto the base of an extruded aluminium box. This box was then screwed onto the power transfer disk.

All assembled ready to test.

After the PCB's were assembled and I finally figured out that I had the 12c wires backwards I managed to get some lights out of my circuit.

 I used a scrap disk of plastic to mount onto the motor drive shaft. I screwed the pcb box lid onto this. To make a commutating slip ring arrangment, in the side wall of the disk I used a lathe to turn two flat bottomed grooves. I then drilled to holes from the floor of the grooves to the top of the disk. I wrapped some copper wire around the grooves and then up the holes. These wires were then wrapped around some screws set into the disk to make power terminals.  Using another smaller disk on the perifery I drilled two holes where some sprung electric motor brushes could slot in. Once all screwed together it worled perfectly. With the filter capacitors I didn't have any problems with power dips or glitches.

 I rigged up a mosfet and signal generator to create a pwm motor controller. I needn't have bothered as the motor was only running at 2/3 rated voltage peak and this was too slow.  Next time I'll over rate it and use a controller like this to bring it down to the correct speed.

 Here are some pics of the first test drive.

TeddyBearMan and some other 11:11 camp members helping me assemble Rare Angles at Burning Man in Nevada 2007.    

In its fullest glory on the Wednesday Night.

Another LED spinner. Using 121 micro controllers ( I used 1) and 120 LEDs ( I used 90). This system had a microcontroller for every rgb led group. Each microcontroller a 3 3bit d/a outputs giving each led group 512 possible colours.

Using a nifty serial communication the central microcontroller would say "led group 23 turn blue" then like chinese whispers the command was passed to the first microcontroller in the chain and it would apply the routine;

Is address group = 0? if yes then act on instruction and then delete instruction.

if no subtract 1 from the address and pass it on.

So by the time this command reaches the 23rd LED group the group number is =0, it turns its output blue and deletes the instruction, then waits for the next input on the serial line.

I thought that was pretty slick. 

The end. 

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