LED shades

Light Emitting Dance shades – general purpose party accessory.

LED Shades v0.3

LED Shades v0.3

About this project

I believe many young adults like to party and with the rapidly growing EDM community a lot of people attend parties with electronic music. I am one of them and you can probably tell where I got the idea to make the LED shades. Projects like this one don’t just keep me occupied in my free time but are also designed to broaden my knowledge in electronics and programming.

I want to share what I have learned working on this project and that’s why I’m making it open-source. I hope this would encourage someone to follow my steps in building the LED shades themselves while exposing design flaws and advantages. This would push the project further and eventually make the shades better for all of us.

Lens from wayfarer style sunglasses are taken out and replaced by circuit boards with 69 LEDs on each. Every LED can be separately controlled much like pixels on 5×7 display. Both left and right circuit boards have a STM32F0 micro-controller for driving the LEDs wired in a matrix. Among with the LEDs there are also other peripherals such as:

  • I2C bus which enables both sides of the shades to communicate with each other,
  • MEMS motion sensor (accelerometer) to track head movements,
  • microphone to make glasses react to music,
  • light sensor to make glasses react to light,
  • a button for changing modes/effects currently displayed ,
  • LiPo/LiIon battery charger,
  • mini USB connector for charging and connectivity with a windows based application,
  • vibrating alert motor,
  • extra ADC input for experimenting, status LED, battery voltage monitor, USART connector for bluetooth to enable connectivity with an android based phone.

 

Short demonstration how the shades look on me:

Schematics

Block-schematics of the whole system

Block diagram of the whole system

 

Click the picture to see the schematics in PDF form.

Schematics master preview - v0.3

Schematics – master (left) v0.3

Schematics slave preview - v0.3

Schematics – slave (right) v0.3

LED matrix

Driving 69 LEDs separately would require at least 69 pins which is inefficient. To reduce pin number and thus minimize MCU’s footprint and cost LEDs have to be wired in a matrix and constantly scanned. This is a good article on how LEDs in matrix work written by Make Magazine.

LEDs

I used standard single color 0603 LEDs I had at home. I checked the datasheet and calculated the current limiting resistor value with the 80% of the rated absolute maximum current that can flow through the diode. I did that in order to make LEDs as bright as possible. Because the matrix is constantly being scanned a single LED is turned on just 1/8 of the time (matrix is scanned vertically and has 8 rows). Effective current through a LED is just 10% of the absolute maximum (which is around 6 mA).

LEDs connected in a matrix

LEDs connected in a matrix

Switching

Dual P channel (dual just to reduce footprint area) MOSFETs are switching rows (horizontal) and dual N channel MOSFETs are switching columns (vertical). I used PMDT670UPE and counterpart PMDT290UNE transistors manufactured by NXP. They are cheap, have low drain to source resistance while open and most importantly they have a very small footprint (SOT666 1.7 x 1.3 mm)

Dual P channel MOSFET

Dual P channel MOSFET

 

MCU

I decided to go with STM32F0 series because of cost and support for crystal-less USB. After some research I chose STM32F042G6 in UFQFPN28 case with 4×4 mm footprint. It has 12 bit ADC which is suitable for audio processing. I managed to use all pins on both controllers for either driving the matrix or connectivity with the peripherals.

STM32F042G6U6

STM32F042G6U6

3-to-8 line decoder/demultiplexer

At first I thought the MCU would have enough pins but at about 60% into drawing the schematics I realized it won’t. I solved this issue with an external 74HC138BQ 3-8 line decoder. It is very cheap and takes only 3.5 x 2.5 mm of area in QFN package. Outputs are inverting (LOW active) what makes it perfect for driving P channel FETs.

3 to 8 line decoder

3 to 8 line decoder

Programming connector

Because of lack of space programming is done with the TAG connect. I think it’s convenient because it takes less space than other solutions. It also does not require any soldering. You can get TAG connect footprint for Altium designer here.

TAG connect – source: www.tag-connect.com

Power supply and management

Supply

Power is supplied from an external LiIon batter-y/ies with integrated protection circuit. I’m using two 200 mAh LiPo batteries each mounted on one side of the glasses. They should last for about two hours of use.

Management

Voltage delivered by battery varies with the charge in the battery so some kind of management and regulation had to be implemented.

Vcc line regulator

TPS63031 buck/boost switching regulator with fixed output of 3.3V regulates the input voltage. It is rated for 1.2A and makes a perfect choice with 2.5 x 2.5 mm footprint. It requires an external inductor and input and output capacitors.

Buck/boost fixed 3.3V switching regulator

Buck/boost fixed 3.3V switching regulator

Single push button on/off

The input of TPS63031  is constantly connected to the battery and in shutdown mode when the device is not being used. Shutdown current is only few uA and I calculated it would take around 10 years to completely discharge the battery. Take a look at the bottom picture.

Single push button on/off.

Single push button on/off.

Let’s assume that the device is in shutdown mode. POWER net is connected to Enable pin of the switching regulator. Pull-down resistor prevents the device to power on. When someone pushed the S1 button the battery potential minus the schottky diode voltage drop (0.3V) is forced on the POWER net what causes the regulator to turn on and MCU to boot. Once the MCU is booted it sets the PA15 pin to high. The button can now be released. When the device needs to be shut down another press on the button once again forces the battery potential on the POWER net, however, it also forces it on the PB6 pin and since the MCU is operating (it wasn’t before) it detects that input pin PB6 is high and sets PA15 pin to low. Device is still functioning as long as the button is pushed down. Once the button is released pull-down does the trick and pull POWER net (connected to enable pin of TPS63031 ) to ground what makes the device to shut down.

Battery charging

MCP73811, a 500 mA charger IC is on board. It has both CC and CV modes and manages them automatically. It is powered from USB’s Vbus (5V) and works as linear drop-down regulator. It produces some heat and requires some copper around it on the PCB to ensure good thermal conductivity and dissipation. Like any linear regulator this one too requires external capacitors. IC is in SOT23-5 housing and has a status pin. It is used to either monitor the charge status with a gpio pin on the MCU or with a LED which stays on during the charge and turns off when the battery is fully charged.

Lipo/LiIon 5V charger

Lipo/LiIon 5V charger

 

Sensors

Sensors make the LED shades react to movement, light and sound.

Movement

The shades can track head movement with LIS3DH MEMS motion sensor (accelerometer). It does not only output data on I2C but also have two interrupt pins that can be programmed to trigger at various events. I chose this sensor because it’s simple and cheap. I also have around 100 of them at home. In addition the sensor features three 12 bit ADCs of which I only used 2. One for temperature sensor (with NTC thermistor) and one for measuring battery voltage.

LIS3DH motion sensor

LIS3DH motion sensor

Measuring battery voltage

Because the voltage of the battery can be grater than the supply of the ADC in the motion sensor a divider has to be used. However, just a resistor divider isn’t enough because it would slowly but surely drain the battery. That can be solved with either using extremely large resistors with a great impact on measurement accuracy or with a transistor that switches the divider on just when it is needed. A single N channel MOSFET is there to enable the divider. POWER net is the same net that enables the Vcc rail regulator.

Voltage divider with enable

Voltage divider with enable

Light

Active element for light sensing is TEMT6200FX01, a phototransistor commonly used in LCDs with automatic brightness. It is cheap, simple and with 0805 footprint. Gain is set with collector resistor. Emitter resistor is there to compensate for thermal drift of the transistor.

Phototransistor as light sensor

Phototransistor as light sensor

 

Sound

Sound pickup is done with a 4 mm electret microphone capsule. The most standard audio pre-amplifier MAX4466 is used to produce usable signals. Because only low frequency sounds are needed to extract the ‘beat’ or tempo from music the passive elements around the amplifier are calculated to work as a light low pass filter. Output of the amplifier is directly connected to ADC where it is sampled and processed.

Electrec microphone and amplifier with MAX4466

Electret microphone and amplifier with MAX4466

PCB design

Due to small size the layout and routing was quite complex. Small holes enable the user to actually see through the glasses. Boards have 2 layers and are routed with 6 mil clearance and 6 mil minimum trace width. There are components on the front and on the back side. The master side (left) is more dense with components since it has got power management.

PCB prototyping

Prototype PCBs were manufactured by PCBWay. Their rapid prototype service is fast (5 days from gerbers to PCBs in my hands), reliable and the quality of the PCBs is completely comparable with a local manufacturer. Not to mention 20 boards with 6mil clearance were just 30$ including shipping. I’ll definitely order again.

Click on the logo to visit PCBWay.com

Click on the logo to visit PCBWay.com

 

PCB prints

Click the pictures to see prints in PDF form.

PCB - master

PCB – master

 

PCB - slave

PCB – slave

 

LED shades

Standard sunglasses lenses replaced with printed circuit boards.

Gerbers

Gerbers v0.3 – left

Gerbers v0.3 – right

Gerbers v0.4 – left

Gerbers v0.4 – right

Versions

Current version: v0.4

Difference between v0.1, v0.2, v0.3 and v0.4

The first version of the board has few errors such as shifted pins on a 3-8 line decoder footprint and misplaced components. Besides that the majority of the board functions as expected. The new version (v0.3) features bigger holes, resistors just on the vertical side of the matrix and a vibration alert motor. Version v0.2 was designed but never fabricated due to new ideas and
consequently a new version – v0.3.

v0.4 is for now the final version where everything should work and all footprints are correct. Use v0.4 gerbers for PCB fabrication.

Bill of materials

The (almost) complete bill of materials with short part description can be accessed on this link. As I buy most components on farnell the BOM also has farnell codes in it.

Prototypes

IMG_2177

First prototype with power management and sound/light

This was the first part of the prototype circuit. It contains power management such as 3.3V switching converter, LiIon charger and protection circuit. On the same board is also a test circuit for light sensor and microphone amplifier. The test circuit became fully functional after fixing some layout mistakes and tweaking some values of passive elements. In the end I decided to get rid of the battery protection based on low part availability and the fact that most of small batteries already have protection built-in.

IMG_2198

First prototype of the LED matrix and de-multiplexer

Second test circuit was with a matrix and a multiplexer. With this one I tested how fast can the MCU scan the matrix. The refresh rate of the whole matrix was 72 kHz (14 us) which is 72 times faster than 1 kHz design requirement.

Test of the PCB shape

Test of the PCB shape

The last thing to test was how well I copied the shape of the lens. Second version fit perfectly.

PCBs with a stencil – first professionally manufactured prototype

After all prototypes I was confident enough to order the first PCBs. As expected they came with some design mistakes. The biggest one was shifted pins on a footprint of demultiplexer. I had to perform so called micro surgery of electronics and imitate a bonding machine to solder the component, twice.

All pins are shifted for one pin CCW

All pins are shifted for one pin CCW

 

LED shades displaying animations and text.

Software

 

Software can be found on github repository.

Implemented features:

  • LED matrix driver
  • LIS3DH driver
  • I2C communication
  • ADC initialization for light sensor
  • Font
  • Custom animations

Future features:

  • Running text
  • Audio processing
  • Single button on/off
  • USB support

New in November 2016: Shades editor, Windows application for editing animations or graphics shown by the shades. C# project is on GitHub.

Shades Editor, the application

Shades Editor, the application

To compile, install Visual studio community, the “Free, fully-featured IDE for students, open-source and individual developers”.

Licence

Licence.txt

14 Comments

  1. required says:

    wouldn’t it be enough to put the resistors only at the outputs of the H line drivers if you’re going to be scanning them anyway?

  2. Janez D. says:

    Congratulations for Hackaday publish!

  3. Preston D. says:

    This is a pretty neat design! Is the multiplexer footprint an issue in the gerbers or in the manufacture? (essentially if I were to print the PCB from the current gerbers would I have to go through the same wire-bonding process as you?) Can I order these from you or do I need to assemble my own???

  4. mmosta says:

    Cool idea, beautiful execution.

    Thank you for taking the time to write everything up and make the design available 🙂

  5. Rok says:

    very nice design…
    Congrats !!!

  6. Edu says:

    Awesome project. Thanks for sharing it to the community.

    Regards.
    Edu

  7. JD says:

    Hi! ,

    I want to order the pcs from pcbway, which settings did you order them with ? the quoting is more expensive of what you wrote (for me) but I might be doing something wrong.

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