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Tag Archives: pwm

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!

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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.

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