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Just a quick one on a thing i discovered today. I ordered USB-compatible, RED, waterproof LED strip from an eBay seller. as expected, i received 50cm strip with a USB cord, but taking a closer look, i found out that it’s actually a flex-PCB for RGB LED strips.

RRR_off

and in fact, the package of the LEDs is a classic 6-pin 5050. weird: the resistors are all the same. and here’s why:

RRR_on

it looks as if they just used their regular RGB LED manufacturing process but instead of bonding and R, G and B chip into the package, they bonded just three R chips. a colleague pointed out that these LEDs might be the result of a failure in the manufacturing process, but i also ordered those strips in warm white, and guess what: 6-pin 5050 package, RGB-strip flex-PCB and three white chips inside the LEDs.

are single-color LEDs still a thing? probably not…

So yes, after the WS28xx revolution (that is dedicated LED controllers or even LEDs with integrated controllers), the problem of controlling a lot of (RGB) LEDs has almost vanished. but then you dig out this box with a LOT of RGB LEDs in it that are just waiting to be PWM controlled. you are not gonna throw them out, are you?
when i learned about Elco Jacobs’ amazing ShiftPWM Arduino Library, i knew all i needed was a little general purpose driver board to light all that LEDs up. the library basically uses shift registers and a high frequency serial signal in order to PWM control a lot of LEDs on just three Arduino pins. handy enough, i was introduced into etching PCBs at the same time, so there it was, my first etching project.
the LEDs i was dealing with were square modules containing three or four 5050 RGB LEDs (common anode). so besides generating the PWM signals, i also needed amplification, because those things run on 12V and consume around 200mA each. we had a bunch of ULN2803 available in the lab, which already served me well in other LED projects.
i designed a board that was easy to manufacture, single sided and chainable. it is called ALLtheLEDs because it can control all the LEDs we found.

alltheledsboard

we built several of those driver boards which are chained and hooked up to an Arduino. they only contain the 74HC595D shift registers, the ULN2803 darlington arrays and blocking capacitors. the data lines run separate from the power lines. each board provides 24 channels, enough for 8 RGB LEDs and up to 30V / 500mA per channel. one of these boards was used to control our rainbow kitchen:

rainbowkitchen

now we also had bags of regular 5mm RGB LEDs in the lab, and on top of that we had a lot of SMD TLC5916 chips. those nifty devices are basically shift registers with an integrated current control for LEDs. this means you do not need resistors for each LED, you just hook up one single resistor to the chip to configure the current per channel. apart from that, they work just like regular shift registers. i designed another board for those chips and simply called it ALLtheOtherLEDs:

alltheotherledsboard

this board is also capable of driving 8 RGB LEDs, but at a maximum of only 120mA per channel. i use one of those boards to control several light sculptures, for example this one:

sculpture

the Eagle files for ALLtheLEDs and ALLtheOtherLEDs are available in my repository:

)))project files(((

if you have any suggestions or questions, please comment!

Ah, the bliss of populating THT circuits on manufactured PCBs… just follow the silk-screen and you’ll be fine. in contrast, the fun-factor of soldering perfboard is way lower. your eyes move from your plan (if you happen to have one) to the board and back, your brain is trying to mirror the layout while you flip the board back and forth all the time. while this might be OK for a single board, what if you have to assemble two? or three? or even more?

for my latest project, i have to populate 10 identical boards. why not have a PCB manufactured, you may ask. well for different reasons: first, it’s too expensive, because the boards are rather large. secondly, i have to get rid of a larger amount of perfboard. third, the layout is not complicated enough to justify a manufactured board.

anyway, in a former similar project, i used a CNC mill to plot the traces onto the board:

plotted pcbs

this was extremely helpful, but setting up the files and the mill took some time. now in the recent project, i experimented with toner transfer to not only put the layout on a perfboard but also a silkscreen on the top. the result is a board that is as easy and flawlessly to assemble as your first beginners electronics kit back in the day and it is neither complicated nor time comsuming:

bothsides

although this is supposed to be some kind of tutorial, i’m not going into details about the toner transfer process, because this is described in other tutorials.
the base of the process is to have a board layout. i normally create layouts even for my perfboard circuits in Cadsoft Eagle. if you set the grid to 0.1 inch and stick to 90 degree angles, you’ll be fine. after that, you usually print out the layout and use it as a template while soldering.
but soldering is still pain in the rear. so why not spend a few minutes with a laser printer, an iron and a sip of water to create a professional perfboard™?

first, i CNC’ed out the boards, because they have a rather odd shape.

milling

if you have no access to a CNC, just use a hacksaw, jigsaw, scroll saw, chainsaw, dynamite, whatever. if you cut your boards manually, you maybe want to cut it after the silkscreening to have an outline for cutting.

for the toner transfer, laserprint the layout onto a piece of catalog or anything else that does not absorb the toner. you may want to stick to one of the toner transfer tutorials i linked earlier for details.
now it gets a little counter-intuitive: keep in mind that during ironing, the layout gets mirrored. that’s why you should only mirror the TOP layer before printing, not the bottom layer. it’s a good idea to print out of Eagle directly. printing into a PDF first is likely to result in unwanted scaling of the layout.

bottom

top

printed_layout

this is a little tricky: you have to carefully align the perfboard grid to the layout grid. i made good experiences with aligning towards a window or a ceiling light, then holding both layout and board with two fingers, carefully putting it on a table upside down and carefully taping it into place. did it mention that you should be very careful? before ironing, check the alignment again.

alignment

putdown

taped

ironing

after ironing, let the board cool down and put in into a bowl of water. peeling/rubbing off the paper is easy if done underwater (only the board and your hands need to be under water). if you decided to do layout AND silkscreen, just repeat the whole process, but be sure not to iron the second layer too long, because you will re-liquify the toner on the other side and the board will stick to the surface.
satisfied? then go solder your professional perfboard™.

heap

stack

detailtop

summary of things to keep in mind:

* print directly out of Eagle/yourLayoutSoftware
* mirror the top layer, print bottom layer normal
* carefully align layout and perfboard grid
* check alignment before ironing
* iron second layer only half a minute or so

if you have any questions or ideas to improve the process, please do comment!

UPDATE: here’s timelapse of soldering the board. it took about one hour and the video is speed up 10x:

Widerstand ist zwecklos” is german for “resistance is futile”, but also “resistor is useless”, which is absolutely the point in this project. i teamed up with my dear friend jan and we created a device that measures resistance and displays it as a resistor color code. an optional cheat mode also displays the resistance as a decimal number. needless to say it is shaped like a giant resistor.

complete_naked

‘just because’, we decided to integrate all electronics into the tube instead of putting it into the base. we also chose to use perfboard and not a dedicated PCB because we had all the parts leftover from different projects and this one is more of a recycling project.

segments

the heart of our resistor is an ATmega168 microcontroller in an uncomfortably large DIL28 package. along with the microcontroller we use a 7805 for voltage regulation and a 4511N BCD to 7-segment decoder/driver for the extra display.

pcb_top

we multiplex the three RGB-LEDs and the 7-segment displays using BC846 transistors as drivers. in order to save some space, we decided to use SMT for transistors and other passive components.

transistors

the resistor is made of dark grey PVC pipe. RGB LEDs and 7-segment displays are integrated into acrylic discs that form the rings of the resistor. in order to embed the displays, we had to CNC a custom disc.

display_multiplex

to perform the actual measurement, we experimented with measuring the resistance by the discharge time of a capacitor. the problem: the measurement takes some time, so the user does not receive an instant measurement when she connects the probes to a resistor. so we decided to rather use a voltage divider and the ADC of the ATmega. the problem this time: we wanted to cover a large range of resistances. so if you use – let’s say a 1K resistor as the constant resistor and measure a 1K resistor, you measure a nice 50% value at your ADC, let’s say 512. if you measure small resistances, like for example 10R and 12R, you cannot safely distinguish between those two because both lead to very very small ADC values. our solution was to use two voltage dividers, one with a 150R constant resistor and the other one with a 27K. we determined this values with some spreadsheeting.

calculations

the resistance is measured with both voltage dividers. threshold values decide if the measured value lies in the safe range of the first or the second voltage divider. as a result, we were able to cover the E12-series over more than 5 decades. in other words: from 10R to 1M

measureclose1

the firmware displays a fancy colorful animation if the line between the probes is open. if a resistance is measured, the ADC value is compated to a lookup table. the closest value from the E12 series is selected and the correspondent colors are displayed. cheatmode is activated if a resistance is measured during power-up. it is sufficient to bridge both terminals with your fingers to do so. if cheatmode is active, you get an additional decimal display of the resistance value.

measuring

feel free to take a look at the calculations, scripts, firmware and schematics:

))) project files (((

if you have any questions, please do comment.

UPDATE: the device is now used as a temperature sensor, connected to an NTC. although my brain is still struggling to figure out the mapping from temperature to colors :)

additional images:

solderin

pcb_bot

digits

opened_display

display_down

measureclose

In the beginning of 2011, i was asked to create some light effect for electronic music partys. it had to be robust and simple, the budget was just 200 Euros. my first thought was obviously an LED matrix. but as i experienced in my former matrix projects, these things can be expensive. after a short brainstorming, we came up with the following concept: we decided to build single panels that contain five RGB LEDs in a row. these panels can be mounted on the ceiling and are either distributed in the room or combined to form a matrix. the design was kept very simple and therefore cheap, which allowed us to build a few panels with the budget and extend the project if more money is available.

time was short, so we went for five panels to end up with a 5*5 matrix at the first party. we bought slats, stapled them together and ended up with ladder-like constructs that were 3.3 m long and 0.4 m wide. some fabric was used as a diffusor. an ATmega168 and some transistors on a breadboard control the five LEDs and the thing looked like this:

 

as you can see, the angle of radiation of the LEDs seperates the singe ‘cells’, making it possible to display clear ‘pixel’ images later on. since a breadboard is not the most robust solution for electronics and manufacturing PCBs would have been to time-consuming/expensive, i used perfboard and throughhole components. i routed the board in Cadsoft Eagle and used a CNC mill with a pen as a plotter to draw the traces onto the boards before soldering. this made it easy to reproduce them and place the mounting holes. no more messing around with mirrored Eagle printouts and forgotten traces. optimized like that, soldering went pretty fast, about an hour for a complete board.

plotted pcbs

so what’s on that board? as the brain, i still use the ATmega168. ULN2001A darlington arrays drive the LEDs and a 1489N RS232 receiver changes the +-12V signal to 0-5V. the voltage regulation is handled by a 7805, dirty but inexpensive. the complete board costs around 10 Euros. as connectors for the power supply, i chose 4 way MOLEX power connectors because they are cheap, robust and reverse polarity protected. for the data line, standard SUB-D9 connectors are used. the boards are designed to be daisychained, so power/data in on one side and power/data out on the other side.

ajolicht pcbs

power is supplied by an old ATX PSU. i use the 12V line and regulate down to 5V on the single boards. this is done to overcome voltage drops when using a long power line and many boards.
the data stream that controls the panels is generated by an old laptop running some python scriptage on a linux system.

AjoLicht matrix half hanging

all panels share the same RS232 line. this is possible because they only receive. each panel has it’s own address and can thereby be controlled individually, so it does not matter if you want to control one or fifty panels. the firmware on the panels handles the datastream, generates the PWMs via binary coded modulation and performs a gamma correction.

the protocol for data transmission is rather simple:
'A',address,15 bytes of data (5xRGB)
represents a data package for one panel, 17 bytes in total.
here’s a video of the finished five-panel, 3*3 m matrix:

 

the panels so far survived 3 partys, rough handling and beeing stored under bad conditions.
so yes, this is the billionth LED matrix, but this time, it’s large scale and really cheap, easy to build and makes a cool illumination for partys. and it always surprises me how you can still amaze people with a bunch of blinking LEDs.

specs in short:
* panel is 3.30m x 0.4m
* costs for each panel: 25 Euros
* 5x superflux RGB LED per panel
* RS232-bus
* 24 bit color depth
* ~80 FPS @ 5 panels in a matrix

feel free to download the source files including firmware sources, example python script and eagle files.

))) project files (((

if you have any questions, please do comment.

About a year ago, i joined a group of hackers to take part in the Nokia Push Challenge, which was basically a hacking contest brought up to advertise the N900 smartphone that was released at the end of 2009. The teams were asked to come up with creative ideas to use the phone.
The Solderin’ Skaters wanted to equip a skateboard with motion sensors in order to use it as a real life gamecontroller for a skating game running on the smartphone. the skateboard sends 6-DOF IMU-data to the phone via Bluetooth. a software on the phone uses datamining in order to detect the tricks the skater performed and award those with points in the game.

skateboard complete

i was one of the two hardware people that build the skateboard. the electronics were designed by the other guy and my main task was to mount them to the skateboard, sp o in this post, i will only focus on this aspect of the project.
what sounds simple at first is in fact fairly difficult. besides the strong vibrations while riding the skateboard, huge g-forces are applied to the electronics when you land a trick. another problem is that almost every part of the skateboard is exposed to kicks, scratches and impacts, which has to be kept in mind when searching for a spot to mount the electronics. additional constraints are Bluetooth connectivity and the sensitive LiPoly battery that powers the system.

spacer closeup

we decided to put everything between the deck and the trucks of the skateboard. therefor i designed a special mounting consisting of four important parts. first a frame that holds the electronics in place and protects them from impacts. second a set of transparent covers that allow to observe the status LEDs on the PCB. another important component is a custom foam rubber cushion that surrounds the PCB in order to damp vibrations and impacts. finally a thin piece of PVC separates the LiPoly battery from the PCB and keeps it safe inside the truck.

spacer montage

all parts were designed in a CAD software and CNC milled afterwards. after some try and error in the design, the results were pretty satisfying. the skateboard has been in sporadic use for about a year now and it still works fine.

besides the Push Challenge, we presented our work at the ACE 2010, the 7th International Conference on Advances in Computer Entertainment Technology in Taiwan.

demo of the application:

links:
solderinskaters.net, infos about the project
Solderin Skaters @ Flickr
Nokia Push Challenge

While relaxing on a beach in spain back in 2006, an idea came into my mind. i wanted to build an LED display. fullcolor and large. no large resolution, just large in terms of dimension. in december 2006, i made actual plans for the project. from there on, i experimented, prototyped, programmed and soldered from time to time. having no deadline made it a real long time project. but then in 2009, i had my 10×10 pixel RGB LED matrix, a square meter of color and light.

matrix with its creator

i guess most of you are particularly interested in some facts about the hardware and software. first the hardware. i used 100 Superflux RGB LEDs with an angle of radiation of about 100°. the LEDs are dimmed via 8-bit PWM, generated by ATmega8 microcontrollers. each controller is responsible for 4 LEDs, which makes it a total of 25 controllers, running at 14,7456 MHz. there are 4 controllers on each PCB, the outputs are amplified by darlington arrays.

guts of the matrix

every LED has it’s own small board, including resistors for each color channel. the pixels are separated by a grid made of 4mm plywood. the light in each pixel is diffused by a small piece of air filter material and the frosted plexiglas pane. diffusion was a major problem, and i guess it’s not really possible to achieve perfect diffusion. my solution is a tradeoff between good diffusion and complexity.

pixels seperated by a grid

the data comes from a PC via RS232(USB adapter) at 460800 baud. all controllers read the RS232 line simultaneously and are addressed by a reserved byte in the data stream. so i broadcast the data to all controllers and each one picks the data it is supposed to read. i’ve reached frame rates beyond 100 FPS.

the final software was written in JAVA because of the OS independency. it is still in development and will probably always be. at the moment it is capable of playing back animations which are stored in bitmaps, displaying the game of life and some variations of it, simple particles and several colorful effects and filters. and of course multiplayer tetris with overlaying playfields. can drive up to three sane persons really nuts.
the matrix was always supposed to be some entertaining decoration element, so it has to be able to generate an endless variety of content without steady user inputs. so i let the software surf the internet and jump from link to link. on every website, it collects content. at the moment, its just an image of the whole website, but i plan to analyze for example the text on the website. the image of the website is analyzed to get it’s n main colors, which are then the basic colors of graphical effects. i hope to end up with some kind of AI which analyzes the web in-depth and shows a simulated creative behavior in dealing with forms, colors and movement. but that’s an utopia right now and it’s gonna be a long way.
another plan was to add some kind of interactivity, but the design is not optimized for adding sensors. maybe a webcam could be used as a proper input-device.
future plans for the hardware include the integration of a netbook to have a completely standalone device which connects to the internet via wifi or ethernet. i considered some embedded solutions, but as old netbooks get cheaper and cheaper, this would be a reasonable solution

if you want to have detailed information about the development and the building process of this project, please visit the project’s own blog
http://rgb-led-matrix.blog.de (german)

Spending some time optimizing my prototyping-tools, i finally got the atmega8-basic-circuit i searched for. i don’t need things like onboard MAX232 or FTDI, because i have modules for that. what i wanted was some AVR-module that is robust, compact and features a crystal, a pullup and ISP. here it is:

brickAVR lit

i soldered a row of female pin headers directly to the AVR-pins. they have a distance of 0.4″, so you could fit a custom protoboard-shield on top of the module. a 16 MHz-SMD-crystal was glued under the chip and connected to the pins, and so was the pullup. i glued an 6-pin ISP-header to the front of the chip and connected it to the appropriate pins. last but not least  i added an SMD-LED to indicate power-on.  that was it for the electronics. next i filled the space between the female pin headers and above the atmega with hotglue (sticking the led into it). finally i needed a case. i had some lego bricks lying around on the desk and more randomly picked one that seemed to match. amazingly it fit perfect after i clipped the sides of the ISP-header. so i glued the circuit into the hollowed brick and added a label i made in corel draw. that’s about it.

the module is powered by the programmer (USB) and i can access every single pin. i like to use it in prototyping applications where a whole breadboad would be overkill, fragile or simply too large. like when you  just want to create a specific output signal. the module also easily hooks up to a breadboard. here’s another two pics of the lower side and the raw circuit:

While messing around with twi (that’s what atmel calls i2c) some time ago, i built this little device that does nothing more than listening to the bus and display all the bytes it receives on a two-digit 7-segment-display in hex-format. the motivation for this project was not only “i need this thing” but also “i’m tired of coding and want to solder something. and i have to get rid of these displays anyway”. the schematic and layout was done in eagle. an atmega8-controller (overkill) handles bus and display. the whole device is powered by the bus.

here’s two pics:

top side of i2c-slave

bottom side of i2c-slave

yes, i forgot one line :(

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