New Musical Instruments

Two of my new musical instruments, and one old one.

The two boxes will soon run SuperCollider.

redAlertLight

For a new piece I'm working on (redAlert), I wanted hundreds of red LEDs attached to special 'blobs' or lamps spread out on stage (designed by Jenny Michel). Each led should be able to be freely placed and controlled individually and they had to be fairly bright. And because of the custom led placement I couldn't have used led strips - strips have a fixed distance between the LEDs.

So I built three circuits that could drive 32 PWM channels each and thereby got 96 PWM channels in total. Each channel connects three LEDs in series (in a single package) and a resistor. That makes in total 288 LEDs.

The led I selected was the LED 5252 uh rt/1700mcd. It has 120 degrees spread angle and comes in a 5x5mm 6pin SMD package that's possible to solder by hand. I bought it from Segor where it costs 0.42 Euro if you buy +100.

Here a picture of it from the backside. The 270 Ohm resistor is chosen to match 12V and the three LEDs are connected in series using thin copper wire.

The three boards are controlled wirelessly and I send OSC commands from SuperCollider to control all the LEDs. There's a class for SuperCollider attached below that helps with addressing and packaging of the network data. One can build and connect as many of these 32ch boards as one likes.

For actually generating the 12V PWM I used on each board two TLC5490 in combination with four ULN2803a. and I also added a barebone Arduino to get a stable SPI communication with the TLC5490.

Backside...

For receiving wireless OSC data I added a Raspberry Pi (model A) with an USB WLAN stick. On the RPi there's just a small Python program that receives OSC and sends out serial commands to the Arduino.

Last I have a TP-link TL-WR703N with Open WRT installed acting as a router. When the boards start, they try to connect to this router and gets an IP assigned dynamically. This IP I use in SuperCollider to differentiate between the three boards.

Installation instructions

* put 2013-09-25-wheezy-raspbian.img on an SD card with Pi Filler
* put the card in a Raspberry Pi MODEL B, connect ethernet and 5V
* find the IP with LanScan.app

(* ssh-keygen -R 192.168.1.51)
* ssh pi@192.168.1.51
* default password: raspberry
* sudo raspi-config
* select 'Expand Filesystem', change password, reboot and log in with SSH again

* sudo apt-get update
* sudo apt-get upgrade
* sudo pico /etc/inittab
* comment out the line 'T0:23:respawn:/sbin/getty -L ttyAMA0 115200 vt100' near the bottom and save
* sudo pico /boot/cmdline.txt
* remove 'console=ttyAMA0,115200 kgdboc=ttyAMA0,115200' and save
* sudo reboot

* sudo apt-get install python-serial
* git clone git://gitorious.org/pyosc/devel.git
* cd devel
* sudo ./setup.py install
* cd ~

//--set up WLAN on the RPi
* sudo nano /etc/network/interfaces
* edit to say...
  auto wlan0
  allow-hotplug wlan0
  iface wlan0 inet dhcp
    wpa-ssid SSID_NAME
    wpa-psk SSID_PASS
    wireless-power off
* sudo ifdown wlan0
* sudo ifup wlan0

//--copy file from laptop to RPi
* scp redAlertLight.py pi@192.168.1.51:/home/pi/

//--automatically start the Python program at startup
* sudo pico /etc/rc.local
* add the following before the exit line: (sleep 1; python /home/pi/redAlertLight.py) & # autostart

//now move the SD card over to model A, connect the circuit and try

//--useful if you log in via SSH and want to stop the Python program
* sudo pkill python

Here is the Python code...

#redFrik 2013

import serial
import socket
import OSC
import threading
import time
import os

addy= '0.0.0.0', 15000  #from SC
osc_server= OSC.OSCServer(addy)

port= serial.Serial('/dev/ttyAMA0', 115200)  #to ATmega168
port.open()

def osc_led(addr, tags, data, source):
  #print tags
  #print "incoming OSC data: %s" % data
  arr= bytearray()
  arr.append(254)
  for val in data:  #data has size 16 (24bit ints)
    hi_val= val>>12
    lo_val= val&4095
    #here can be optimized later to send fewer bytes (48 instead of 64)
    arr.append(hi_val>>8)
    arr.append(hi_val&255)
    arr.append(lo_val>>8)
    arr.append(lo_val&255)
  arr.append(255)
  port.write(arr)

osc_server.addMsgHandler("/led", osc_led)

def osc_stop(addr, tags, data, source):
  #print tags
  #print "shutting down"
  shutdown()

osc_server.addMsgHandler("/stop", osc_stop)

thread= threading.Thread(target= osc_server.serve_forever)
thread.start()

def all_led_off():
  osc_led(None, None, [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0], None)

def shutdown():
  close()
  os.system("sudo halt")
  exit()

def close():
  print "\nclosing"
  osc_server.close()
  all_led_off()
  port.close()
  #thread.join()

def main():
  try:
    while True:
      line= port.readline()
      if line.startswith("stop"):
        shutdown()
  except KeyboardInterrupt:
    close()

if __name__ == "__main__":
  main()

Attached are schematics, Arduino firmware, parts list...

redThermoKontroll2

For my upcoming solo at the Sound of Stockholm festival, I decided to rebuild my main wireless controller. Previously it used a Nordic nRF24L01+ transceiver as radio module, but the range wasn't great and communication often broke down during live performances. I don't know much about these things, but I guess that when the audience bring in mobile phones the radio spectrum quickly fills up.

So I constructed a new circuit from scratch and while I was at it also reworked the resistor ladders and other cablings inside the box. Now it's using WiFi. The new radio module I installed in the controller box is Adafruit's CC3000 WiFi Breakout, and as receiver, I use a small tl-wr703n WiFi router running OpenWRT.

The wireless range is now excellent and everything is a lot more stable. I could also drastically reduce the amount of data being sent by fixing the resistor ladders.

Circuit... (basically just one ATmega382p, a 16 channel ADC, voltage divider resistors and the WiFi module)

Inside...

Outside...

100 Ohm resistor ladder...

Below are parts list, schematics, firmware and a SuperCollider class.

redThermoKontroll (WiFi version) parts list:

1   4067 multiplexer
1   ATmega328p
1   16 MHz crystal
2   27p ceramic caps
1   socket 2x14 (28pin)
1   Adafruit CC3000 module
1   1x9 pin header
1   1x10 pin header
1   1x8 pin header
1   1x5 pin header

1   resettable fuse 1A
1   Zener diode 5.6V
1   0.1uF cap
1   100uF electrolytic cap
1   470uF electrolytic cap

10  220, 270, 330, 680, 1K, 2, 10K resistors
1   220 resistor for led

1   power jack
1   LDR
1   red led

//redThermoKontroll2
//redFrik 2013 GNU GPL v2
//updated 150920 - automatically send to IP x.x.x.99 (constructed from given DHCP IP)

//make sure to use Paul Stoffregen's branch of the Adafruit_CC3000 library
//and cc3000 firmware 1.24 (1.11.1)
//select board UNO and upload to a ATMEGA328P chip (using a usbtinyisp programmer)
//test in terminal with command: nc -ul 58100

#include <Adafruit_CC3000.h>
#include <ccspi.h>
#include <SPI.h>

#define WLAN_SSID       "xxx"
#define WLAN_PASS       "yyy"
#define WLAN_SECURITY   WLAN_SEC_WPA2

#define PORT            58100
#define DELAY           10
#define PINGRATE        2000

#define ADAFRUIT_CC3000_IRQ   3   //mega328 pin 5
#define ADAFRUIT_CC3000_VBEN  8   //mega328 pin 14
#define ADAFRUIT_CC3000_CS    10  //mega328 pin 16
Adafruit_CC3000 cc3000 = Adafruit_CC3000(ADAFRUIT_CC3000_CS, ADAFRUIT_CC3000_IRQ, ADAFRUIT_CC3000_VBEN, SPI_CLOCK_DIVIDER);
Adafruit_CC3000_Client client;

uint8_t buf[16];
byte last[] = {
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
};

byte cnt = 0;
unsigned long time;

void setup(void) {
  Serial.begin(115200);  //debug

  //--pins
  pinMode(7, OUTPUT);         //led
  pinMode(6, OUTPUT);         //4067 d (DDD6)
  pinMode(5, OUTPUT);         //4067 c (DDD5)
  pinMode(4, OUTPUT);         //4067 b (DDD4)
  pinMode(2, OUTPUT);         //4067 a (DDD2)
  pinMode(A5, INPUT);         //4067 x
  pinMode(A4, INPUT_PULLUP);  //capa1 (right)
  pinMode(A3, INPUT_PULLUP);  //capa0 (left)
  pinMode(A2, INPUT_PULLUP);  //swiUp (up)
  pinMode(A1, INPUT_PULLUP);  //swiUp (down)
  pinMode(A0, INPUT_PULLUP);  //swiOn

  //--wifi
  flash(1);
  Serial.println(F("Starting"));
  if (!cc3000.begin()) {
    Serial.println(F("Unable to initialise the CC3000! Check your wiring?"));
    while (1);
  }
  flash(2);
  Serial.println(F("\nDeleting old connection profiles"));
  if (!cc3000.deleteProfiles()) {
    Serial.println(F("Failed!"));
    while (1);
  }
  cc3000.connectToAP(WLAN_SSID, WLAN_PASS, WLAN_SECURITY);
  Serial.println(F("Connected!"));
  flash(3);
  Serial.println(F("Request DHCP"));
  while (!cc3000.checkDHCP()) {
    delay(100); // ToDo: Insert a DHCP timeout!
  }
  uint32_t ipAddress, netmask, gateway, dhcpserv, dnsserv;
  while (!cc3000.getIPAddress(&ipAddress, &netmask, &gateway, &dhcpserv, &dnsserv)) {
    Serial.println(F("Unable to retrieve the IP Address!"));
    delay(100);
  }
  Serial.print(F("\nCC3000 IP Addr: "));
  cc3000.printIPdotsRev(ipAddress);
  //the following sets receiver to x.x.x.99 and assume cc3000 will never get exactly that IP itself
  ipAddress = cc3000.IP2U32(ipAddress >> 24 & 255, ipAddress >> 16 & 255, ipAddress >> 8 & 255, 99);
  Serial.print(F("\nReceiver IP Addr: "));
  cc3000.printIPdotsRev(ipAddress);
  client = cc3000.connectUDP(ipAddress, PORT);

  //--OSC message [/tk2, index, value]
  buf[0] = 47;   // /
  buf[1] = 116;  // t
  buf[2] = 107;  // k
  buf[3] = 50;   // 2
  buf[4] = 0;
  buf[5] = 0;
  buf[6] = 0;
  buf[7] = 0;
  buf[8] = 44;   // ,
  buf[9] = 105;  // i
  buf[10] = 0;
  buf[11] = 0;
  buf[12] = 0;   //msb - index
  buf[13] = 0;   //
  buf[14] = 0;   //
  buf[15] = 0;   //lsb - value
}

void loop(void) {
  byte val;

  //--analogue inputs
  for (byte i = 0; i < 13; i++) {
    setChan(i);
    delay(1);                //not sure if needed
    val = analogRead(A5) >> 2; //from 10 to 8 bits
    if (val != last[i]) {
      sendOsc(i, val);
      last[i] = val;
    }
  }

  //--digital inputs
  val = PINC & 0b00011111;
  if (val != last[13]) {
    sendOsc(13, val);
    last[13] = val;
  }

  //--ping
  if (millis() - time > PINGRATE) {
    sendOsc(127, 0);      //ping
    time = millis();
  }
}

void sendOsc(byte index, byte val) {
  buf[12] = index;
  buf[15] = val;
  if (cnt++ % 2 == 0) {   //toggle red led
    PORTD &= ~_BV(DDD7);
  }
  else {
    PORTD |= _BV(DDD7);
  }
  client.write(buf, sizeof(buf));
  delay(DELAY);
}

void setChan(byte index) {
  switch (index) {
    case 0:
      PORTD &= ~_BV(DDD2);        //low
      PORTD &= ~_BV(DDD4);        //low
      PORTD &= ~_BV(DDD5);        //low
      PORTD &= ~_BV(DDD6);        //low
      break;
    case 1:
      PORTD |= _BV(DDD2);    //high
      PORTD &= ~_BV(DDD4);        //low
      PORTD &= ~_BV(DDD5);        //low
      PORTD &= ~_BV(DDD6);        //low
      break;
    case 2:
      PORTD &= ~_BV(DDD2);        //low
      PORTD |= _BV(DDD4);    //high
      PORTD &= ~_BV(DDD5);        //low
      PORTD &= ~_BV(DDD6);        //low
      break;
    case 3:
      PORTD |= _BV(DDD2);    //high
      PORTD |= _BV(DDD4);    //high
      PORTD &= ~_BV(DDD5);        //low
      PORTD &= ~_BV(DDD6);        //low
      break;
    case 4:
      PORTD &= ~_BV(DDD2);        //low
      PORTD &= ~_BV(DDD4);        //low
      PORTD |= _BV(DDD5);    //high
      PORTD &= ~_BV(DDD6);        //low
      break;
    case 5:
      PORTD |= _BV(DDD2);    //high
      PORTD &= ~_BV(DDD4);        //low
      PORTD |= _BV(DDD5);    //high
      PORTD &= ~_BV(DDD6);        //low
      break;
    case 6:
      PORTD &= ~_BV(DDD2);        //low
      PORTD |= _BV(DDD4);    //high
      PORTD |= _BV(DDD5);    //high
      PORTD &= ~_BV(DDD6);        //low
      break;
    case 7:
      PORTD |= _BV(DDD2);    //high
      PORTD |= _BV(DDD4);    //high
      PORTD |= _BV(DDD5);    //high
      PORTD &= ~_BV(DDD6);        //low
      break;
    case 8:
      PORTD &= ~_BV(DDD2);        //low
      PORTD &= ~_BV(DDD4);        //low
      PORTD &= ~_BV(DDD5);        //low
      PORTD |= _BV(DDD6);    //high
      break;
    case 9:
      PORTD |= _BV(DDD2);    //high
      PORTD &= ~_BV(DDD4);        //low
      PORTD &= ~_BV(DDD5);        //low
      PORTD |= _BV(DDD6);    //high
      break;
    case 10:
      PORTD &= ~_BV(DDD2);        //low
      PORTD |= _BV(DDD4);    //high
      PORTD &= ~_BV(DDD5);        //low
      PORTD |= _BV(DDD6);    //high
      break;
    case 11:
      PORTD |= _BV(DDD2);    //high
      PORTD |= _BV(DDD4);    //high
      PORTD &= ~_BV(DDD5);        //low
      PORTD |= _BV(DDD6);    //high
      break;
    case 12:
      PORTD &= ~_BV(DDD2);        //low
      PORTD &= ~_BV(DDD4);        //low
      PORTD |= _BV(DDD5);    //high
      PORTD |= _BV(DDD6);    //high
      break;
  }
}
void flash(int num) {
  for(byte i= 0; i<num; i++) {
    digitalWrite(7, HIGH);
    delay(100);
    digitalWrite(7, LOW);
    delay(100);
  }
}

p5 Tweets

Constrains - I love them. Inspired by Abe's twitter experiments, I've also played with creating small one line Processing programs that are 140 characters long.

Below is a video of number 0002, the twitter code tweets and screenshots. Note that many but not all are animations. Copy and paste the lines into Processing (2.0) to try them out.

NOTE: several stopped working under version Processing 3 and above. To make them run replace size(s,s); with size(900,900); i.e. width and height can no longer be variables.

0001

int i;noStroke();size(999,900);for(i=0;i<999;i++){fill(255,0,0,9);rect(i%99,i,i,i);}for(i=0;i<999;i++){fill(0,200,0,3);rect(i,i,i,i);}// #p5

0002

int j,i=0;void setup(){size(1200,900,P3D);frameRate(999);}void draw(){for(j=0;j<99;)rect(i++%(1199-j++),int(i/99)%(999-j),i%12,j%16);}// #p5

0003

int s=900,j,i=j=0;void setup(){size(s,s);fill(0,9);textSize(80);}void draw(){text(i+j,(sin(i++)/3+0.3)*s,(cos(j+++(i/4e3))/3+0.5)*s);}// #p5

0004

int s=900,j,i=j=0;void setup(){size(s,s);stroke(255,9);fill(9,3);}void draw(){quad(i++,j++,j,i,s-i,i-50,s-j,j);i=(i<<j%4)%1200;j=j%s;}// #p5

0005

int s=900,i=0;void setup(){size(s,s,P3D);stroke(255,0,0);fill(10,4);}void draw(){translate(i++%s,s/2);rotate(float(i)/s);sphere(i%s);}// #p5

0006

int s=900;float i=0;void setup(){size(s,s,P3D);stroke(99,9);fill(0,2);}void draw(){translate(i++%s,s/2);rotate(cos(i/50));box(i%s/3);}// #p5

0007

background(0);noStroke();for(float i=0;i<99;i=i+0.0252){size(1200,900,P3D);fill(255,0,0,60);translate(i+9,i);rotate(i*1.8);sphere(i);}// #p5

0008

void setup(){size(1600,900);background(255);}void draw(){textSize(millis()%1200);fill(second()*4,0,0,second());text(millis(),10,880);}// #p5

0009

float j,i=0;void setup(){size(1200,900,P3D);}void draw(){for(j=0;j<133;j++){rect(9*j+1,sin((i+++j)*0.75/cos(j/99)/5e3)*99+450,9,9);};}// #p5

0010

float i,k=450;void setup(){size(900,900,P3D);textSize(k);}void draw(){translate(k,k);fill(i%1*k/2,60);rotate(i+=+.01);text("$",99,0);}// #p5

0011

int i,j,k=1200;void setup(){size(k,900);fill(255,200);}void draw(){background(0);for(i=0;i<8e3;)text(i++*j/k%k,i%131*9,i/131*16);j++;}// #p5

0012

int j=200,i=900;size(j*6,i,P3D);lights();translate(700,540);for(i=1;i<j;){fill(i/2,50);rotate(j/i);translate(i,i,-2.7);sphere(i+++j);}// #p5

0013

int j=480,i=900;size(j*3,i,P3D);noStroke();lights();translate(660,j);for(i=1;i<j;){fill(i,0,0,10);rotate(i/4e4,1.1,2.2,3.3);box(i++);}// #p5

0014

int s=900,i=0;void setup(){size(1200,s,P3D);}void draw(){translate(600,450);rotateX(i*.0021);fill(i++%256,30);sphere(sin(i*.0014)*s);}// #p5

0015

int i,s=900;void setup(){size(s,s);frameRate(1e4);stroke(255,25);}void draw(){fill(i++%89,0,0,127);rect(i%90*9,i%91*9,i*i%92,i*i%93);}// #p5

0016

int i,s=900,t=1200;void setup(){size(t,s);noStroke();}void draw(){fill(i++%256,25);quad(i%t,i/3%s,i/4%t,i%s,i/5%t,i/4%s,i/3%t,i/2%s);}// #p5

0017

int t=0;void setup(){size(900,900);background(0);stroke(255,9);}void draw(){translate(450,450);line(sin(t)*421,cos(t++)*400,t%9,t%9);}// #p5

0018

int s=900;size(1600,s);fill(255,9);while(s>9){rotate(1e-3);arc(s+420,s,s,s,0,7);arc(1000-s,s+100,s,s,0,7);arc(s+500,400-s,s,s--,0,4);}// #p5

0019

int i,j,s=900;void setup(){size(s,s,P3D);smooth(8);}void draw(){stroke(i);line(i,j,s-j,i);if(j%5<1){i=(i+1)%s;}if(i%11<1){j=(j+i)%s;}}// #p5

0020

int s=900;void setup(){size(1200,s,P3D);}void draw(){fill(s,50);translate(sin(s)*110+600,cos(s)*99+450);rotate(s);box(s);s=(s+1)%900;}// #p5

Arduino Programming via Soundcard

With lots of study of the AudioBoot_V2_0 Java code by Chris at roboterclub-freiburg.de, I managed to write SuperCollider code for uploading sketches to an Arduino via the soundcard. no FTDI chip needed!

It's a very cheap solution for programming barebone Arduinos (well, ATmega168 microcontrollers really). You only need a few resistors, a capacitor and a mega168. The only difficult part is to 'initialize' this microcontroller by burning the special bootloader on to it. This requires an AVR programmer of some sort (STK500, USBtinyISP etc).

The preparation steps are as follows...

1. Burn the bootloader on to a mega168
2. Build the barebone circuit
3. Prepare the Arduino IDE
4. Install the RedArduino class

After that one can compile HEX files in the Arduino IDE and upload them using SuperCollider and a standard audio cable.

1. Burn the bootloader on to a mega168

The trick behind all this is the special 'sound enabled' bootloader that I found here... www.hobby-roboter.de/forum/viewtopic.php?f=4&t=127. I downloaded the AudioBoot_V2_0.zip file and used my STK500 AVR programmer together with the great AVR Crosspack. The terminal command I used for burning the bootloader was the following...

avrdude -v -p m168 -b 115200 -P /dev/tty.PL2303-000013FA -c stk500v2 -U flash:w:/Users/asdf/arbeten/sc/scAudioino/AudioBoot_V2_0/Atmega_Source/chAudioBoot_ATMEGA168_IN_PD1_LED_PB5.hex -U lfuse:w:0xE2:m -U hfuse:w:0xDF:m -U efuse:w:0xFA:m

2. Build the barebone circuit

Then I built a minimal and barebone Arduino circuit after the schematics found here... www.hobby-roboter.de/forum/viewtopic.php?f=4&t=128&p=531. Again credit to Chris.

This is the schematics I drew...

And here the resulting circuit...

I run it off 4.5V (3 batteries) but it could also be powered from the USB port.

3. Prepare the Arduino IDE

To compile HEX files for this barebone Arduino, I needed to set up a custom board in the Arduino IDE. One way to do this is to create a new text file called boards.txt and put it inside a new folder in the Arduino/hardware folder. on macOS that could be something like ~/Documents/Arduino/hardware/BareBones/boards.txt. The boards.txt should contain the following...

minimal168.name=ATmega168 bare bone (internal 8 MHz clock)
minimal168.upload.speed=115200
minimal168.bootloader.low_fuses=0xE2
minimal168.bootloader.high_fuses=0xDD
minimal168.bootloader.extended_fuses=0×00
minimal168.upload.maximum_size=16384
minimal168.build.mcu=atmega168
minimal168.build.f_cpu=8000000L
minimal168.build.core=arduino:arduino
minimal168.build.variant=arduino:standard

Then restart the Arduino IDE and under boards, there should be a new option with mega168 and 8 MHz internal clock. I make sure this board is selected every time before compiling HEX files for sound uploading.

Another thing that needs to be done is to enable 'verbose compile' in the Arduino IDE preferences. That will print out the file path of the HEX file each time you compile a sketch.

4. Install the RedArduino class

I wrote a couple of classes for SuperCollider to help with the encoding and signal generation of HEX files. They're found in my redSys quark (under redTools) and are most easily installed from within SuperCollider itself with these commands...

Quarks.install("redSys");  //install. recompile after this

There are two helper classes and one main class. The RedIntelHex class parses HEX files and RedDifferentialManchesterCodeNegative helps to encode the signal as differential manchester code. The main class RedArduino figures out the paging of data and generates a bitstream that is played back using demand rate UGens.

Uploading

I upload sketches by compiling them in Arduino IDE (click verify - not upload) and copy&paste the file path of the resulting HEX file into SuperCollider and the RedArduino's read method. I connect the left sound output channel to the barebone Arduino, put my mac laptop volume to ~80%. Last I press the reset button on the circuit and quickly (within seconds) call the upload method in SuperCollider. The led should blink slowly directly after a reset, and fast when receiving data.

Here's a video demonstrating how to do it. I'm just uploading the simple Blink example. Near the end, you will also hear how that sounds.

There's also some SuperCollider code I wrote (github.com/redFrik/udk09-Bits_and_Pieces/blob/master/udk130523/extras/uploadingArduino.scd) that will do the same thing but without the need of the redSys quark classes.

Trash or Treasure?

Some weeks ago I found a Canon Pixma MP510 on the street. A "Photo All-in-One with economical single inks that prints, copies or scans in colour". Someone had thrown it away regarding it as a piece of junk. I saw a pile of gold.

Taking it apart I got...

• four nice motors: two stepper and two DC motors
• a 33x25 cm piece of glass
• boxed and reusable 220V power supply
• a small LCD colour display
• a scanner head
• some LEDs
• five infrared sensors (paper sensors)
• lots of screws and springs
• wire and cog belts
• some switch buttons
• two USB jacks
• various other components

Alike makezine.com/projects/dont-waste-ewaste-unmaking-a-canon-printerscannerfax-into-parts/

USB Soundcards Mod

To save a bit of power (and annoyance), I de-soldered the LEDs on two USB soundcards. I use these soundcards for battery-driven projects (Beaglebone Black) and every milliamp I can save counts.

The LogiLink soundcard had two easily removable LEDs. The red one indicated that the soundcard was connected and had power, and the green one started to blink when the card was in use (driver activated). Both functions I can easily live without.
The blue '3D-sound' card had a very tiny surface-mount led that I removed using two soldering irons.

Here some before and after photos...

Btw, I'd stay away from the LogiLink. It has a problem with audible noise coming from the PWM signal of the green blinking led. If you connect a mic like I'm doing, a beep beep beep kind of sound leaks into the mic. And removing the led doesn't help. Maybe there's something in the software driver to control it, but I doubt it.

Cheap 4-channel Videoplayer

For the dance piece Ich(a) by Zufit Simon I constructed a system with four Raspberry Pi mini-computers and buttons to trigger playback of four video streams. As the videos didn't need to run in exact frame-by-frame sync, this was a very cheap way to get four channel high-quality video playback. Total cost was about (RPi 28 * 4) + (SD card 6 * 4) + (5V power 1 * 7) ≈ 141 Euro. I chose the model A of the Raspberry Pi to keep the cost and power consumption down. The four computers share a 5V power supply of 2 amps and are powered over the GPIO pins. Video cables run 50 meters down to the stage and into separate flat-screen monitors. The monitors are built into boxes that can be piled up or rolled around independently.

The videos are stored on the 4 GB SD cards that also holds the Linux operating system. I converted the videos from DVD to MP4 using ffmpeg with the following settings...

ffmpeg -i concat:"/Volumes/MONITOR01_may2012_DVD/VIDEO_TS/VTS_01_1.VOB|/Volumes/MONITOR01_may2012_DVD/VIDEO_TS/VTS_01_2.VOB" -an -vcodec libx264 -profile:v high -preset fast -crf 18 -b-pyramid none -f mp4 MONITOR01_may2012.mp4

That'll take two chapters and convert to a single MP4 and skip the audio track (-an flag).

The Python program running on each computer is here below. It plays a video to the end and waits for a button trigger. If a button is pressed before the video is finished, it'll stop and jump to the next video - all in a cyclic fashion.

#f0videoplayer.py
#for a Raspberry Pi running Raspbian
#this script will cycle through videos in sequence when a GPIO pin is grounded

#pinSwi (pulled up internally) - GND this pin to switch to the next video
#pinOff (pulled up internally) - GND this to shut down the system

#--settings
videos= ['/home/pi/ICHA1.mp4', '/home/pi/MONITOR01_may2012.mp4', '/home/pi/BLACK.mp4', '/home/pi/FLESH.mp4', '/home/pi/TESTBILDER.mp4']
delays= [0, 0, 0, 0, 0]  #extra start delay time in seconds - one value for each video
pinSwi= 23
pinOff= 24

#--
import pexpect
from time import sleep
import RPi.GPIO as GPIO
import os
GPIO.setmode(GPIO.BCM)
GPIO.setup(pinSwi, GPIO.IN, pull_up_down= GPIO.PUD_UP)
GPIO.setup(pinOff, GPIO.IN, pull_up_down= GPIO.PUD_UP)

def main():
  os.system("clear && tput civis")  #clear and hide cursor
  index= 0  #keeps track of which video to play
  while True:
    sleep(delays[index])
    omx= pexpect.spawn('/usr/bin/omxplayer -rp '+videos[index])
    omx.expect('Video')  #play
    while(GPIO.input(pinSwi)==True):
      sleep(0.1)
      if GPIO.input(pinOff)==False:
        omx.send('q')  #quit
        os.system("tput cnorm && sudo halt")
        exit()
    omx.send('q')  #quit
    sleep(0.5)  #safety
    while(GPIO.input(pinSwi)==False):
      sleep(0.01)
    index= (index+1)%len(videos)

if __name__ == "__main__":
  main()

Instructions for installing

(you'll need a model B to prepare an SD card, but then move it over to the model A Raspberry Pi)

prepare the RPi

• use Pi Filler to transfer 2013-05-25-wheezy-raspbian.img to the SD card
• put the SD card in RPi model B
• select 'Expand Filesystem' in and enable SSH under advanced in config menu
• select 'Finish' and reboot
• log in with pi/raspberry
• sudo apt-get update
• sudo apt-get upgrade
• sudo apt-get install python-pexpect avahi-daemon

copy files from macOS

• open a terminal window on the main computer
• cd to folder with videos
• edit the file f0videoplayer.py and select which videos to use
• optionally add delay times if some videos should start later
• scp f0videoplayer.py MONITOR01_may2012.mp4 ICHA1.mp4 BLACK.mp4 FLESH.mp4 TESTBILDER.mp4 pi@raspberrypi.local:/home/pi/

back to model B

• sudo pico /etc/rc.local
• add the following before the exit line: (sleep 1; python /home/pi/f0videoplayer.py) & # autostart video player
• press ctrl+o to save and ctrl+x to exit
• sudo halt

start model A

• take out the SD card from model B and put it in model A
• connect HDMI or composite video, GPIO pins and apply power - the first video should start
• ground pin 23 to cycle through the videos
• ground pin 24 to turn off the computer

Useful commands

(connect a keyboard to RPi model A, type pi/raspberry to log in)

sudo pkill omxplayer.bin #might need to write this without the terminal being visible

if you get "WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!"

ssh-keygen -R raspberrypi.local     #useful for resetting ssh/scp after changing SD cards

It's not pretty but it's working. Some day I'll build it into a real rackmount box.

References

www.raspberrypi-spy.co.uk/2013/06/playing-videos-on-the-raspberry-pi-command-line

www.raspberrypi.org/phpBB3/viewtopic.php?f=38&t=47520