From Mobile March 2014-A quick look at creating Arduino-based wearable electronics, complete with design files. Learn the basics of building and programming an LED light strip built into a headband. The session covers programming, battery basics, sound activation, and construction techniques.

2. Goals
• Light you up!
• Show a simple example
• Give you a place to start
…
#3: LED Strip
+5VDC
#4: Battery
Clock
Data
LM2596 Adjustable
A0
D3
D
2
5
V
G
N
D
GND
#1: Arduino
Board#2: Microphone
Module
O
U
T
V
C
C
G
N
D
#5: DC-DC Converter
HEADBAND
BATTERY PACK POWER CONVERTER CABLE
(20) LEDs
1.25V

3. Agenda
• Why this project
• How it’s designed
• Where it could go

4. Why
• Skrillex was coming to town!!!
• What could we bring to the concert?
– LED Hats – too easy to steal
– LED Shirts – too ordinary
– LED Wristbands – not easily seen
– LED Skirts – not me! *
– LED Necklaces – too easy to break
• Decided on headbands
– Easy to make
– Easy to hide
– Should be cheap
* See Kristina’s presentation at 2:15PM !!

5. Where to Get Started
• Three major components:
– Headband
– Battery Pack
– Power Converter Cable
• Needed four sets
• Might get broken, stolen or confiscated, so
they had to be cheap.
• Maximize reuse of past projects
• Maximize reuse into future projects
Budget was $200 and schedule was 2 months

6. Block Diagram
…
#3: LED Strip
+5VDC
#4: Battery
Clock
Data
LM2596 Adjustable
A0
D3
D2
5V
GND
GND
#1: Arduino
Board#2: Microphone
Module
OUT
VCC
GND
#5: DC-DC Converter
HEADBAND
BATTERY PACK POWER CONVERTER CABLE
(20) LEDs

7. Major Design Decisions - 1
#3 LED Strip: decided to use a LPD8806-based LED Strip
1. LED Strip was chosen by convenience = I already had 2+ meters
2. Brightness set by LED Strip choice = 10mA to 15mA/LED
3. Number of LEDs set by head size = 20 LEDs
Therefore: LED strip needs roughly 300mA at full brightness
4. System voltage set by LED Strip voltage, which = 5V
5. Arduino and microphone power considered negligible
Therefore: Power needs are appr. 300mA x 5V = 1.5W
#4 Battery: Li-ion battery pack (rechargeable, high energy-density), 18650
cell size (2600mAH, popular) in a 3-cell pre-assembled pack, 11.1V
6. Battery technology needed to be rechargeable (for reuse)
7. For power, battery needed to provide 1.5W for several hours
8. Battery voltage needed to be > (5V + minimum regulation voltage)
9. Battery needed to fit in pocket or purse
10.Pre-assembled packs, with built in protection for over-charge, low-voltage
shutoff, short-circuit, etc. – safer, less hassle
Run Time
SizePower

8. Major Design Decisions - 2
#5 DC-DC Converter: picked a LM2596 based DC-DC converter
11.Regulator needed to have an input of 11.1V and output needed to be 5V
12.Regulator needed to handle > 300mA, 500mA preferred
13.Regulator needed to be efficient to avoid heat and maximize run-time
14.Regulator needed to be small and light weight
#1 Arduino: picked SparkFun Pro Micro, 5V version, based on size
15.Arduino voltage needed to be 5V to match LED Strip voltage
16.Arduino board size needed to be as thin as the LED strip ~ 0.5” to 0.7”
17.Arduino board needed at least one analog input and two digital outputs
#2 Microphone Module: AdaFruit P/N 1713 Electret Microphone Module
18.Microphone needed to have a built-in amplifier
19.Microphone needed to run on 5V
20.Microphone needed to have adjustable sensitivity
21.Microphone needed to be as thin as the LED Strip
22.Update: automatic gain control!!

9. #1: Arduino Board
• SparkFun Pro Micro
• Dimensions: 1.3” x 0.7"
• Features:
– ATmega32U4 - 5V/16MHz
– Supported by Arduino IDE
– Onboard Micro-USB
– 4 x 10-bit ADC pins
– 12 x Digital I/Os
– $20

10. #2: Microphone Module
• AdaFruit P/N 1713
• Small Electret Microphone
• Built-in microphone amp
• Auto Gain Control (AGC) –
variable sensitivity!
• 5V Operation
• $8

11. #3: LED Strip
• Popular LPD8806 Controller IC
• Sold 32 to 52 LEDs per meter
• Approximately $20 to $30 per meter
• Available from multiple sources on eBay

12. #4: Battery Pack
• Li-ion for size, power
density and recharging
• Pre-assembled w/ built-in
protection circuitry
• 11.1V output can be
regulated down to 5V
• 2600mAh size should
last several hours
• Small enough to fit into a
pocket or purse
• $30

13. #5: DC-DC Converter
• DC-DC Converter Module (LM2596 IC)
– Input: 4V to 35V – (11.1V battery voltage)
– Output: 1.5V to 30V - adjusted to 5V
– Current: 3A (max) - can handle the estimated
250mA to 300mA
– Small and efficient – 80% to 90%
• Multiple sources
• Appr. $1.25 ea.

14. Rough Costs
1) Arduino = $20.00
2) Microphone = $8.00
3) LED Strip = $11.50
4) DC-DC Converter = $1.25
5) Battery Pack = $30.00
6) Wiring & Plugs = $6.00
7) Headband = $1.25
8) Misc = $1.00
Total cost per Headband approximately: $80 each
Plus: Charger = $18.00
Decided to only build 3 to stick close to budget.

15. General Construction
• See Appendix
– Battery Pack
– Power Convertor Cable
– Headband
• ~1 to 2 hours each

16. Software - 1
/************************************************************************/
/* Headband01: LPD8806-based RGB LED Modules in a strip using audio input
/* lights up all LEDs in a rainbow of color, with variable brightness
/************************************************************************/
#include "LPD8806.h" //the color strip library
#include "SPI.h" //the communication library for strip
#define NLEDS 20 //Number of RGB LEDs in strand
#define AVERAGECOUNT 32 //the number of audio samples to average
#define AUDIO 0 //the analog input channel
#define OFFSET 255 //the DC offset of the microphone module
// Chose 2 pins for output; can be any valid output pins:
#define DATAPIN 2 //connect to the Data In pad on the LED strip
#define CLOCKPIN 3 //connect to the clock pad on the strip
// First parameter is the number of LEDs in the strand. Next two
// parameters are SPI data and clock pins:
LPD8806 strip = LPD8806(NLEDS, DATAPIN, CLOCKPIN);
struct RGB { // a structure to hold the color of a pixel
byte r;
byte g;
byte b;
};

17. Software - 2
/************************************************************************/
/* setup: the initialization code - executes once on reset (power up)
/************************************************************************/
void setup() {
strip.begin(); // Initialize the LED strip
strip.show(); // Update the strip; to start they are all 'off'
}

18. Software - 3
/************************************************************************/
/* loop: the main program - executes forever
/************************************************************************/
void loop() {
int audio = 0; // storage for the averaged reading
for (int i=0; i < 220; i++){
// get an averaged audio sample from the mic then
// draw a rainbow of colors out from the middle
rainbowMiddle(NLEDS, averageDetect(AUDIO), i);
}
for (int i=219; i > 0; i--){
rainbowMiddle(NLEDS, averageDetect(AUDIO), i);
}
}

19. Software - 4
/************************************************************************/
/* averageDetect: Get the average analog voltage on the analog input pin
/************************************************************************/
int averageDetect(int analogIn){
int averageValue = 0; // initialize average value
long int sum = 0; // initial register to hold the sum
int sensorValue = 0; // analog input sample (A/D= 0 to 1023, 0 - 5V)
// read AVERAGECOUNT analog values and find the average
for (int i=0; i < AVERAGECOUNT; i++){
// read the analog voltage (range is 0 to 1024)
// subtract the DC offset of the module and then sum
// the absolute value
sensorValue = analogRead(analogIn) - OFFSET;
sum = sum + abs(sensorValue); //
}
averageValue = (sum / AVERAGECOUNT) ; //calculate the average
return (averageValue);
}
1.25V

20. Software - 5
/************************************************************************/
/* rainbowMiddle: draws lines from the middle of the strip outward
/************************************************************************/
int rainbowMiddle(int peak, int brightness, byte shift){
struct RGB color = {0,0,0}; // the color of a single pixel
int j = NLEDS / 2; // middle of the strip
brightness = 0xFF / brightness;
//Color the strip from the middle out to the ends
// if the position along the strip is less than the peak, color the pixel
// else, turn off all the pixels above the peak value
for (int i = 0; i < j; i++){ // going to mirror the colors
if (i < peak){
// get the color for this position (input range 0 to 384)
color = Wheel((i * 384 / NLEDS + shift) % 384);
strip.setPixelColor(j - i-1, color.r / brightness, color.b /
brightness, color.g / brightness);
strip.setPixelColor(j + i, color.r / brightness, color.b / brightness,
color.g / brightness);
}
else {
strip.setPixelColor(j - i-1, 0, 0, 0);
strip.setPixelColor(j + i, 0, 0, 0);
}
}
strip.show(); //show the new colors - takes ~ 4.66 msec on the Uno
}

21. Software - 6
/************************************************************************/
/* Wheel: Input a value 0 to 384 to get an RGB value from a color wheel
/* The colors transition from r > g > b and back to r
/************************************************************************/
struct RGB Wheel(uint16_t WheelPos){
struct RGB color = {0,0,0}; // storage to calculate the color
switch(WheelPos / 128){
case 0:
color.r = 127 - WheelPos % 128; // Red down
color.g = WheelPos % 128; // Green up
color.b = 0; // Blue off
break;
case 1:
color.g = 127 - WheelPos % 128; // Green down
color.b = WheelPos % 128; // Blue up
color.r = 0; // Red off
break;
case 2:
color.b = 127 - WheelPos % 128; // Blue down
color.r = WheelPos % 128; // Red up
color.g = 0; // Green off
break;
}
return color;
}

22. DEMO

23. Where Could It Go?
• More LEDS!!!
• Cheaper, smaller electronics
• Cheaper, smaller battery
• Washable
• Add light modes
• Add spectrum analysis
• Add light sensor
• Bluetooth to phone
• Get color data from soundboard
• Send individual color data
Run Time
SizePower

24. Questions?
• Thank you for your time!!
• Files at:
https://www.dropbox.com/sh/kmfop133g57
8815/LjwEI3AlPT

25. Appendix - General Construction
• Assemble Battery Pack
• Assemble Power Convertor Cable
• Assemble Headband

26. Battery Pack – Step 1
• Assembled Battery
Pack using (3) 18650
3.7V 2600mAh cells
• Built-in over-charge
and over-discharge
protection circuitry
• Comes w/ 6” wires
• From All-Battery
Center on eBay
• Roughly $30 each

27. Battery Pack – Step 2
• Solder Deans-style to the
battery wires
• Use Female socket for
battery
• Note polarity!
• Be careful not to short
battery wires when soldering
• Use shrink tubing to protect
against accidental shorts

28. Battery Pack – Step 3
• Finished Battery Pack
• Charge with
compatible charger
– eBay: Tenergy TLP-2000
Li-Ion Charger
– Solder Male Deans Plug
to Charger output leads

29. Power Converter Cable
• Converts Battery voltage to 5V
Battery Input
5V Plug To Headband
DC-DC Converter Module
3 Foot Cable

30. Power Converter Cable – Step 1
• Buy a 1-meter 5.5mm/2.1mm Male-Female
Power Cable and cut into two sections
– Female socket side = appr. 6 inches
– Male plug side = remaining length – appr 3 feet
5V Plug From
Power Converter
5V Socket From
Headband

31. Power Converter Cable – Step 2
• Solder 6-inch 22AWG Red/Black wires to input
side of the module
• Solder the 3-foot Male Power Cable to the
output side
– Note the color and polarity of the internal wires
• Adjust trimpot to get 5V on the output

32. Power Converter Cable – Step 3
• Solder Red/Black wires from input side to
Male Deans Plug
• Be sure to use Shrink tubing
• Note polarity
Battery
Power Converter

33. Power Converter Cable – Step 4
• Fold both wires back roughly 0.5 inches from
the module edge
• Secure with tie-wraps to form strain reliefs
• Secure cables to module with tie wrap

34. Power Converter Cable – Step 5
• Use 1.0-inch to 1.25-inch Shrink tubing over
the entire module
• Slightly heat the ends of the tubing and pull
tight with tie-wraps

35. Headband

36. Headband – Step 1
• Cut the LPD8809 strip to 20 LEDs
• Cut along the lines
• Note the direction of the arrows – indicates
which is the “input” end

37. Headband – Step 2
• Solder Data (DAI) and Clock (CLK) lines to thin
flexible wires (26 – 32 AWG) roughly 3-inches
• Solder heavier gauge wire to 5V and GND (22
AWG)

38. Headband – Step 3
• Solder Data to I/O-2 on the Arduino
• Solder Clock to I/O-3 on the Arduino
• Solder Red 5V wire to the Arduino 5V pin
• Solder Black GND to the GND on the Arduino
• Secure wiring with tie-wrap

39. Headband – Step 4
• Solder the 6-inch Female Power cable to the
Arduino’s 5V and GND – confirm polarity!
• Solder 22AWG wires from Arduino to the
Microphone Module
– Blue = Mic-OUT to Arduino A0 (Analog 0)
– Black = GND
– Red = 5V
• Use tie-wrap

40. Headband – Step 5
• Wiring complete!
• Inspect solder joints
• Confirm connections with ohmmeter before
applying power
• Confirm everything with test code!
Note: picture shows older microphone module

41. Headband – Step 6
• Adjust the Microphone
Gain to lowest level
• Solder a short jumper
from Gain to Vdd

42. Headband – Step 7
• Hot Melt Glue can be used to secure wiring

43. Headband – Step 8
• Create supporting plastic band from available
material
• 1” x 19.5” Thin plastic
• Must be flexible

44. Headband - Step 9
• Attach one side of self-adhesive Velcro to back
• Trim other end to aid in threading into
headband

45. Headband - Step 10
• Tape LED Strip to plastic support strip
• Don’t block LEDs

46. Headband – Step 11
• Tape Arduino a bit more securely to protect
wiring
Note: picture shows older microphone module

47. Headband – Step 12
• If there is a logo – twist the Cotton headband
around so the outside is plain
• Cut a 1” slot in the headband
• Attached the other side of self-adhesive Velcro
to the inside of the headband on either side of
the slot
• Carefully thread the assembly into the
headband

48. Headband – Step 14
• Attach half of the
Velcro on the
module to one side
of the slot in the
headband
• Route the power
cable out the slot
• Insert the rest of the
module on the inside
of the headband

49. Headband – Step 15
• Finished installation of the electronics in the
headband

50. Headband – Step 16
• Done!