Chaos Communication Camp 2011

Next week I’m going to Chaos Communication Camp which takes place near Berlin. Every four years the camp provides an exciting opportunity to hang out and work on projects, attend various talks and socialise.

At the camp I’m planning to spend a lot of time in the Hx2 Hardware Hacking Area. I had originally signed up to give a hands on workshop on Introduction to PCB Etching, but I can’t bring the chemicals on the plane. So I’ve come up with another project for a workshop.

The project for the workshop will be to create a custom m0dul for the r0ket badge which can be used to form a Laser Tag system. This m0dul will be designed from scratch including hardware and software starting this weekend and during the camp, though inspiration for parts has come from DIY discussions on the Laser Tag Forums. Materials cost will be approximately €50.

In addition I’ll be bringing ten soldering sets for use in the Hardware Hacking Area, Mini Mood Light v1 Kit, I Can Solder Badge v1 Kit and other bits & bobs.

Just hopping all the parts arrive in time.

MindField

This weekend April 29th to May 1st I’ll be helping to run a hardware hacking area in the Hackerspace Tent at MindField – International Festival of Ideas. Taking place inside Merron Square park in Dublin’s city centre MindField offers a diverse programme of talks, debates and workshops covering various topics on culture, technology, politics and inspiration.

Members from Irelands hackerspaces and makerspaces have been invited to build a temporary hackerspace in the park over the weekend. Giving visitors the opportunity to experience the possibilities of hacker and maker culture in Ireland. We’ll be showing off existing projects, teaching new skills through activities and workshops, and working on new projects with visitors and the resources we’re bringing over the weekend.

In MindField Hackerspace I’ll be helping to run a hardware hacking area teaching people to solder repair and re-propose, and giving a free Introduction to Arduino Workshop. I’ll also be talking part in the Hack the Planet! panel discussion on hackerspaces.

In the hardware hacking area I’ll be selling some of my kits including the Mini Mood Light v1, Dual LED Matrix Display and other LED based displays. All along with Arduino Uno’s, TI LanuchPad’s, electroluminescent wire and hundreds of LEDs.

One very special item I’ll have for sale is a basic I Can Solder kit which is in the form of a badge. The I Can Solder badge was inspired by the Electronic Merit Badge from Make:. Which I had the pleasure of using to help teach hundreds of kids and adults to solder during the Maker Faire UK in March in New Castle, England.

LED Matrix Display

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.

LED Badges

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.