Numeric Node Sketch

Agilent HDSP-A101 (Common Anode)

DS2408 1-Wire 8-Way switch

Interactor set

The new set of interactive pins and the software to drive them are finished. Have been very busy doing this, as well as working on techniques for locating the pins on the surface. I will post pictures and new code soon.

The Reminding Notice Board at EUSAI '04

The demo was presented at this year's European Symposium on European Intelligence, at Eindhoven, NL. I think it went very well - most people seemed to like the concept and enjoyed playing with the demo. It was the first time that the technology really worked when used by other people - due in great part to the much better reliability provided by the new surface materials. The demo has been published in the adjunct proceedings of the symposium (ACM ISBM 1-58113-992-6), pp. 35.

Dual LED pins

The DS2406 switches arrived from Dalsemi after a long waiting time. Apart from the ability to control the state of two PIO pins, the device includes 1kbit of EEPROM of user programmable memory.

The switch worked straight away when using the DS9097U-E25 serial line adapter and OneWireViewer application supplied by Dallas. But there were problems when I tried to use it with the HA5 adapter - the device wasn't even recognized as being on the network! It turns out that the HA5 is tweaked to drive really large 1-Wire networks: hundreds of devices along long stretches of wire. A notice board-sized Pin&Play surface as the one I was using is a relatively small network in comparison, and this results in an impedance mismatch between the device and the adapter. The DS2406 is particularly suceptible to this problem, which explains why it worked fine with the DS2405 and iButton devices.

To solve this problem, the cable connecting the adapter to the surface was modified with a 150Ohm resisor added in series with the signal line. After this, everything worked perfectly. I imagine that if the HA5 is used to drive much larger, wall-sized surfaces the resistor would not be needed.

Idea: Surfaces as networked clients

The people at Embedded Data Systems will shortly be introducting the HA7NET 1-Wire Host Adapter. It will be replacing the HA5 - which I have been using to drive the latest Pin&Play prototype - as their flagship 1-Wire controller. The basic functionality remains the same, providing a simple text interface and the ability to pump additional power into the network. The difference is that instead of an ASCII RS-232 serial interface it will have an Ethernet connector and a TCP/IP interface. This could be used to create an interesting application model for Pin&Play surfaces. The idea is that a single server in the local network runs provides the application and control of the board, and any number of boards can make use of this application by simply plugging them into the LAN. It would remove the need to have a dedicated controller PC per board, while at the same time allowing for the more powerful applications that are difficult to achieve using an embedded device such as a Smart-Its as a network controller.

Notice Board Application Demo

The Notice Board application was demonstrated last Monday at the Equator All Hands Meeting. It had a good reception, people that saw it liked the new hardware and seemed to relate to the application.

The notice board allows notes and documents to be attached onto it by using pins. The pins are colored either red, orange or green - corresponding to three different levels of priority one would assign to a document that was posted on a notice board. This allows a way for the user of the notice board to inform the system when she would like to be reminded of the existence of the document, and the need to pay attention to what it contains. When this time expires, a small light built onto the pin will begin to flash to display this fact. The user must then unfasten the document from the board in order for the pin to stop flashing. Information about when documents were posted, their level of priority and how much time they have before their reminder expires is displayed on a screen nearby. This information can also be accessed via a web interface.

This demo has been submitted to this years European Symposium on Ambien Intelligence (EUSAI 2004), which takes place early November.

Web NoticeBoard

The web server for the NoticeBoard application has been running for the last few days and seems to be working well. It allows people to check the status of the notice board from a web browser by going to this site.

Currently I am redesigning the interface which is very inflexible at the moment. The look and feel will also be changed slightly as a result of this, making it easier on eye.

I have stopped trying to get the old DS2405 switches used in the current pins to work with the HA5 controller. It is definately doable but I am not sure it is worth spending the time on it, as they will not get used when the new ones arrive. The new DS2406 switches should be here soon and they will be much easier to control and read their state, as well as providing a built-in 1kb of memory.

A Broken Pin

A second pin has broken when trying to pin it into the surface. The place where the outer (gold) and inner (silver) sections meet (separated by a plastic insulator) is definately the weak point of the pin. The inner pin becomes very thin at this point as it travels through the outer core. Usually it is not a problem - the pins bend a little with use but they can be carefully straightned. If they bend too much though they are liable to break off like this. They can't really be reinforced, as this would entail making the pin thicker which in turn would make it harder to push into the surface. The solution is probably to experiment with different materials to provide the insulation between the active layers in the surface itself so that the pins don't require so much force to be inserted...

Testing LEDs

Finding the right LED to use in the new pin design is important. How much power the LED consumes will determine how many pins can be powered at any one time. It is also essential to make sure that the LED will be bright enough when powered by the irregular source that the surface provides. I tried a number of surface-mounted LEDs from the Farnell catalogue. The tests were carried out using 4.5V DC power supply and an 8kOhm resistor to simulate the Pin&Play surface.

In the end I chose a pair of blue and a green LEDs made by a company called MARL. Not only were they far brighter than the other LEDs, but the power consumption was really low (about 0.3mA). And the blue ones add several points to the coolness factor of the design.

The Why of One Wire

In an effort to get my head round the lower-level functions of the HA5 adapter, I have been reading up on the workings of the 1-Wire network in general. A comprehensive overview of working with the 1-Wire network explains clearly why and how the protocol does the things it does.

New Pin Design

After two days of learning how to use Eagle CAD properly, I managed to get the program to do my bidding and produce the board layout for the new pin design I had in mind.

The new design features:

- Small size: 1.6mm in diameter, about the size of a 5p coin
- Flatter: It uses all surface-mounted components, so it should be only a few mm thick
- Two LEDs, controllable through a single DS2406 addressable switch which also provides 1kbit of memory
- Better efficiency as the LEDs have much lower power consumption than the standard 3mm ones we were using before.

The LEDs (blue!) arrived today from Farnell, but it will be at least another week before the PCBs arrive and maybe even longer for the switches to arrive from Dallas/Maxim.

The EAGLE 4.1 files are here.