Tag Archives: led

Aurora Lamp

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Aurora LampOver the first weekend in March I took part in the first Science Hack Day Dublin an open data hacking event hosted in Dublin City University. The challenge was for participants to come up with open data related project ideas, to form groups, work on those projects and present the results all within 36 hours.

Some initial project ideas were collected on a wiki page in the days before the Hack Day. Part of a set of interrelated project’s caught the eye of one of the organisers and he suggested that the submitters get in contact with me for some input and maybe to help.

All the Aurora Orrery project’s revolved around the Aurora or in the northern hemisphere Aurora Borealis or Northern Lights. Which are caused by charged particles from the sun effected by the earths magnetic field interacting with the upper atmosphere. The result is a spectacular light show in the sky which is more visible as you get nearer the polar regions. But given a high level of of solar activity and favorable weather patterns, the Aurora can be seen from Ireland in places like Donegal and other parts of Northern Ireland.
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LED Matrix Display

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Last Sunday I gave a workshop in TOG as part of it’s Engineers Week 2011 activities. We spent the day assembling a 8×8 Red/Green LED Matrix Display circuit which I designed in strip board.

The circuit forms an interface between a micro controller and a 8 by 8 Dual Colour Common Anode LED Module. This type of module has two LEDs per pixel, each row has 8 pixels, with 8 rows. The anodes of each LED in a row are connected, with 16 columns formed by connecting together the cathode of an LED from each row.

A high side switch is needed to turn on/off a row and must be able to source approximately 240 milliamperes (16 multiplied by 15 milliamperes). A low side switch is needed to turn on/off a column, but only one LED is on per column so it only needs to sink 15 milliamperes.

For the high side switching I used a TD62783APG 8 Channel High-Voltage Source Driver from Toshiba Semiconductor. It’s very important that only one output from the TD62783 is on at any one time so I used a 74HC238 3-to-8 Decoder from NXP to control the row selection. For the low side switching we used two 74HC595 8-bit Shift Registers from NXP.

Only one row of LEDs is on at a time, the display uses persistence of vision to give the illusion that all the LEDs are active at one time.

The basic operation for displaying a single frame is. The data for a row is shifted into shift registers one bit at a time, the shift register output is turned off (OE), the row is selected on the decoder, the shift register data is loaded into the output registers (LE) and then the shift register output is turned on. These steps are repeated for each additional row of data. All the steps are repeated indefinitely until the next frame of data is to be displayed.

The circuit was designed around the Arduino micro controller but should work with other micro controllers. The connections are shown in the image. The left hand side of the display is the row select pins the central pins are for power and ground, with the columns connected to serial peripheral interface (SPI) pins on the Arduino on the right.

Dual 8×8 Matrix v0.1 Schematic

I’ll do a follow-up blog post with the source code and a Java program I’ve written to create animations.

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LED Badges

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Just after getting back from 27c3 in early January Jeffrey and myself got talking about a project for TOG’s Paddy’s Day hackaton.

Our general idea was to create a little badge with LEDs in the shape of a shamrock. We were hoping for something small, light and bright with lots of LEDs. I said that I would do some more research to see if it would work and if it did to come up with a suitable circuit design.

I knew the general idea was to use a step-up (boost converter) to increase the voltage level so to that I could drive a string of LEDs. I then began to search manufactures sites for suitable components and relevant information.

After searching all the main contenders I found a very interesting range of chips in a small five pin surface mount package from ON Semiconductor. The most interesting options were the CAT4137 LED Driver, Boost, 5 LED and CAT4238 LED Driver, Boost, 10 LED. Another option from Linear Technology was the LT1932 – Constant-Current DC/DC LED Driver in ThinSOT. As I wasn’t sure what would work I ordered a couple of each component and the suggested supporting components. Along with lots of green surface mount LEDs.

I then designed and etched a simple proof of concept board. After soldering it up and connecting up a CR2032 coin cell battery it worked but I was disappointed with the brightness of the LEDs.

I then put the project on hold. Roll on a couple more weeks and I looked at this project again.

Investigating the proof of concept board I realised I had used a wrong resistor value and was trying to supply 30 milliamperes instead of 10 milliamperes into the string of LEDS. Changing this didn’t really help increase the brightness. But it did point me in the direction that I was just trying to draw too much current from the battery.

I found the following blog post on using cr2032 coin cells from Marcus from Interactive Matter (who I meet at 27c3) very informative. Connecting up the circuit to two AAA batteries solved the brightness problem.

I have now reworked the board into a near final layout. And as a token gesture to the 14th of February (Valentines Day) I’ve created a design in the shape of a heart.

Tomorrow I’ll finish the prototype of the shamrock badge and post a picture. If I created a kit would you be interested in buying it?

Update: Here is the photo of the prototype for the shamrock badge. When we looked at it after I assembled the badge it was hard to make out the leafs also I might change the resistor value to increase the brightness.

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Engineers Week 2011

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Next week I’m helping to run a number of events in TOG for Engineers Week.

I’ll be helping Jeffrey with his free Arduino 101 – Learn to Blink on Tuesday, the Soldering Workshop on Saturday and I’ll be giving a new LED Dot Matrix Display Workshop on Sunday (I hope to do a write up soon).

During the week I have a number of Arduino Uno‘s boards available for €30.

Also over the weekend I’ll take part in the Synchronous Hackathon and I hope to have time to help with TOG’s Hackerspace 555 Timer Challenge entry for the 555 Contest.

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Small 16×16 RGB LED Display

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The photo shows a prototype of a small 16×16 RGB LED matrix display that I worked on during 27c3 in the Hardware Hacking Area.

The display is made up of four 8×8 RGB LED modules which are only 32mm by 32mm which doesn’t give much room to work with. Each module has it’s own TLC5947 a 24-Channel, 12-Bit PWM LED Driver from Texas Instruments sinking the columns and a A2982 8-Channel Source Driver from Allegro MicroSystems source the rows. The display is controlled by an mbed NXP LPC1768 micro controller. With a 74HC238 3-to-8 Decoder and a custom switch-mode power supply module rounding out the board.

Coming up with a suitable schematic and layout only took a couple of days as I’ve used all the parts before in other boards. Etching the board and drilling the holes took about two hours on xmas eve. Reviewing the board and schematic on Day 1 I discovered a problem with the way some part were connected. With a craft knife and some future solder bridges I was able to work around the problem. I’ve already corrected the schematic and layout if I decide to make the board again.

On Day 2 after Mitch Altman’s workshop on Arduino For Newbies I began to solder the board. The process was relatively straight forward with mostly surface mount packages in SOIC and TSSOP package types. The most time consuming part was creating vias by soldering a thin wire between the two sides of the board and inserting the last LED module as the drill holes were very narrow. Though in all the soldering took about six hours.

The smoke test was successful in that it found no faults in the board. So I could now move on to programming the mbed by adapting some code from a previous project. The programming results late on Day 2 weren’t great with significant flashing of the display. Though I did discover a soldering fault which didn’t show up during the smoke test.

Day 4 was much more successful after a good nights sleep. So with a fresh head, the basic operation is. Each TLC5947 contains 24 12-bit shift registers which are connected together in series and driven by one of the SPI ports on the mbed, these registers are the source of gray scale data which is controlled by additional pins connected to the mbed. The high side current coming from the A2982′s is controlled by a 3-to-8 decoder also connected to the mbed. The corrected sequence for displaying a line on the display is that the 1153 (24 * 12 * 4) bits of data is loaded into the shift registers through the SPI port, the output is blanked, then the correct row is selected on the decoder, the data latched into the gray scale registers and the output re enabled. Then repeat for the next 7 lines, to draw a full frame.

Now at the end of Day 3 the display and code can easily operate with no flashing, I’m not sure of the refresh rate. I even spent some time working on random graphics and drawing display modes, though I’m sure better results would be achieved by someone else. I’m very happy with the results as I was expecting an out right failure.

Now what? I’ve got some small changes I could make to the board including reducing the brightness of the LEDs by changing some current controlling registers and the software can always be worked on. This was a proof of concept project for a 16×16 display I’ve been working on similar to the cool [Projekt:Bunt] a large 10×10 RGB matrix. So this prototype and any software developed for it should help the testing or running of a larger display.

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