PCB design for pattern matrix 2

This is the pattern matrix 2 tangible sensor schematic, which is fairly simple – just 4 hall effect sensors and a capacitor to smooth out any noise on the power supply.


We need to make hundreds of these for the Penelope Project, and we can save some costs by using the built in pull up resistors in the MCP32017 to get a decent signal from the sensors. The difficulty with this PCB is arranging the sensors so they align with the magnets in the tangible programming block in the optimum manner. From tests with the prototype Lego rig, this isn’t actually too critical – but it’s set up so the lead length can be tweaked a bit at soldering time.


This took me about 20 variations to finally get right, but the circuit is just about simple enough that it can be made single sided – this is good because the top side will be partly exposed, while the lower side with all the copper traces can be protected. It’s good practice to have large areas of copper left connected to ground, partly as it’s a common connection needed all over the board, partly for stability but also it reduces the amount of chemicals required to etch the circuit – as only the parts around the traces need to be removed.


The i2c expander board is a little more complicated. The design is made to be modular so we can stack up any number of these connected to the Raspberry Pi for different arrangements of sensors. Each board can deal with 8 sensor locations (each comprising 4 individual hall effect sensors). Their job is to convert the digital signals from each sensor into serial data (using the i2c protocol) so the Raspberry Pi can read them all just using 2 wires, plus 2 for power.


Each board can be configured to a separate i2c device address to tell it apart from the others using jumper connectors. This one had to be 2 sided, but I managed it without any ‘vias’ (holes to pass traces from one side of the board to another). I also added a power indicator LED as a last minute addition.


I’ve been learning the open source Kicad software to design these, which is now used by CERN for building the LHC, so it’s pretty fully featured! The idea is that you draw the schematic first, link each component with a physical ‘footprint’, then switch to the PCB design stage. Other software I’ve used in the past tries to route everything in one go for you (and can come up with some pretty strange and messy results). Kicad works in a semi-automatic manner – you need to draw each trace by hand, but it routes them around components and other traces, and suggests the shortest path for you. This is quite a lot better than a fully automatic approach as you have more control over the end result, and easily end up with a decent placement of all the parts.


This project is of course open hardware, and can be found on github here.

Pattern Matrix 2 haptic experiments

One of the potential future additions to our tangible programming hardware is haptic feedback, using sound/vibration to provide a extra channel of information through your fingers when programming with tangible blocks. We wanted to test this before designing the PCB hardware in case we could add it to the system simply – this was initiated by watching a reverse engineering video on youtube (I think by bigclivedotcom) where a technique was mentioned for sneakily reusing input lines (of which we have hundreds) as outputs when they are not being read, by using diodes to separate the signals.


Piezo transducers are often used as cheap speakers, and they can also provide some touch feedback by using lower frequencies. We tested one to see if it interfered with the magnetic fields, and the diaphragm doesn’t seem to be ferrous metal (I’m not actually sure what it is made from) so it can be placed right over the sensors with no effect. A bit more Lego to attach it to the prototype sensor unit, and to see we can feel it through the tangible block when it’s touching the sensor.

The first attempt consisted of simply plugging a speaker into the i/o line from the MCP23017 port expander, switching between input and output on the Pi and adding a diode to prevent the output voltage getting to the sensor.


The problem is all the circuits we’re using run on 3.3V, but the piezo speaker I’m using is rated up to 20V – so it’s just not strong enough to feel it. The Pi also provides 5V pins, so a second attempt to use a simple driver circuit (single transistor common emitter amplifier) to boost the voltage:


You can hear this version in the video above – it’s playing a sound using a frequency crudely determined by the 4 bit value the block orientation represents whenever it changes. This is louder (loud enough at least to make a recording) but still not enough to feel easily, even when you put the piezo between the sensor and the block. So it seems the best way to get this to work properly will be via a separate circuit, not something we can slot into the existing input hardware. Another advantage of doing it separately is that we can treat it more like a multichannel audio setup with a dedicated processor that is not interrupted by the sensor reading. One solution I saw was to use the same H bridges as used to drive motors from microcontrollers as these take much higher voltages – this will be something to try later on.

New pattern matrix developments

A few weeks ago we kicked off the new Penelope project, and while in Munich one of our first jobs was to deliver the prototype pattern matrix to the Museum of Casts of Classical sculpture for exhibition over the summer as part of our Penelopean lab. Our next mission in Cornwall is to design new tangible programming hardware so we can start manufacturing a small run of alternative versions with more sensors to try new experiments with them. Some of them will be used for public exhibition, others for the researchers to use in talks and seminars, others for musical livecoding performances.

A big focus for us is the materials and physical design, on the one hand like everything FoAM Kernow builds it needs to be open source and appropriate technology (so easily explainable and built by others) and on the other it needs to be sympathetic to it’s context in the museum, displayed alongside looms and technology that are thousands of years old. This has resonance with the Al Jazari livecoding installation in the Alhambra in 2008, where a juxtaposition of modern and ancient curiously worked. As part of this we want to switch from materials like aluminium and plastic to wood construction – employing similar building techniques to the looms themselves, but more along the lines of inspiration to inform alternative technological choices rather than simple mimicry.

We’re also trying out simpler electronics designs – firstly switching to slightly cheaper hall effect sensors (SS411P from SS411A, previously) and testing different kinds of magnets – which turns out to be the more tricky part to get right. Here is a rare earth magnet test:

Ferrite magnet test:

For environmental and cost reasons ferrite magnets would be much better to use, and they are strong enough to be picked up by the sensors in a useful range – however presumably in order to increase their ‘stickiness’ it appears that ferrite magnets are often magnetised in complex ways, with both poles being present on the same (active) side, and much reduced on the other. This means we can’t use them in the same way, they flip the field on and off with the same orientation and don’t do anything on the other. We’re still searching for a fix for this, but currently the best we can do is reduce the rare earth magnet thickness to 1.5 mm from 3mm used in the prototype.

The prototype was useful for demonstrating that we can use digital signals rather than needing analogue sensors which it was built to allow if the hall effect sensors were not good enough – so a big development is removing the microcontrollers we needed before and replacing them with port expander ICs (MCP23017). These even use the same serial communication we were using (i2c) to talk to the Raspberry Pi so it’s a straight swap.

In order to test the new system all together as well as new magnet combinations and spacing we built a prototype with lego to hold the sensors in the right position, and provide the base for the tangible programming block to rest or be rotated on. This is important to do for the design of the PCB before it goes for production – as we can’t change the sensor position afterwards, more on that part soon.

Picademy Exeter and Future Thinking for Social Living

Last week I had the chance to help out the Raspberry Pi foundation at their Picademy in Exeter. It was good to meet up with Sam Aaron again to talk livecoding on Pis, and also see how they run these events. They are designed for local teachers to get more confident with computers, programming and electronics to the point where they can start designing their own teaching materials on the second day of the two day course. This is a model I’m intending to use for the second inset teacher training day I’m doing next week at Truro school – it’s pretty exciting to see the ideas that they have for activities for their pupils, and a good challenge to help find ways to bring them into existence in a day.


We also had the ending of Future Thinking for Social Living at the Miners Court summer party last week. We exhibited the map made during the workshops, made lots of tea, and had some fun with the pattern matrix in musical mode out in the garden – I adapted Alex’s music system we used with Ellen in Munich to run on Raspberry Pi so it didn’t require a laptop, or a screen at all – simply a speaker. It was interesting how quickly people got the idea, in many ways music is easier to explain than weaving as listening while coding is multi-sensory.


Weavecoding Munich

Ellen’s exhibition in Munich was always going to be a pivotal event in the weavecoding project – one of the first opportunities to expose our work to a large audience. The Museum of casts of classical sculptures was the perfect context for the mythical aspects of weaving, overlooked by Penelope and friends with her subversive woven/unwoven work, we could explore the connections between livecoding and weaving.

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Practically we focused on developing the tangible weavecoding exhibit for events later in the week, as well as discussing the many languages we have developed so far for different looms and weaving techniques. One of our discoveries is that none of the models or languages we have created seem sufficient in themselves – weaving could be far too big to be able to be described or solved from a single perspective. We’ve tried approaches describing weave structures from the actions of the weaver, setup of the loom and structure of the fabric – perhaps the most promising is to explor the story of weaving from the perspective of the thread itself.



One of the distinctive things about weaving in antiquity is how multiple technologies were combined to form a single piece of fabric, weaving in different directions, weft becoming warp, use of tablets vs warp weighted weaving. To explain this via the path of a single conceptual thread crossing through itself may make this possible to describe in a more flexible, declarative and abstracted manner than having to explain each method separately as if in it’s own world.



The pattern matrix has now been made into good shape for explaining the relationship between colour and structure in pattern formation. For the first time we also used all 4 sensors per block on the bottom row which meant we could use a special “colour” block that the system recognises from the normal warp/weft ones and use it’s rotation to choose between 8 preset colour settings. This was quite a breakthrough as it had all been theoretical before.


Adding this more complex use of the magnetic patterns meant that Alex could set up the matrix as a tangible interface for his tidal livecoding software meaning Ellen could join us for a collaborative slub weavecoding performance on the Saturday evening. The prospect of performing together was something we have talked about since the very beginning of the project, so it was great to finally reach this point. The reverb in the museum was vast, meaning that we had to play the space a lot, and provide ‘music for looking at sculptures by':

Tangible programming: detecting flip, rotation and id with magnets

When we started designing the pattern matrix we wanted to include the possibility of encoding more than binary (which side is up) using the magnets. In order to test this, we made the bottom row of sensors with 4 in a square – the rest only have one sensor currently (to avoid blowing the budget on hall effect sensors).

Here are some test blocks with four magnets glued on. The one at the back is easy to make as they naturally snap together edge to edge in this pattern, the closer one required superglue and lots of patience – I’m still expecting it to fire a magnet off unexpectedly at some point:


The orientation seems to work well in our tests so far, as you rotate the blocks the sensors latch from one state to the other – and it seems like they stick to their previous reading until the block is very nearly aligned straight. I’ve added some sound on the Pi to give some haptic feedback which is turning out to be very useful.

The next job was to head back to makernow make some better blocks with the magnets inside. Oliver Hatfield milled out new holes in some of our spares:


Luckily the fit is really tight so with some force the magnets can be placed inside without the need for any gluing – and they don’t rattle around at all:


The next thing was to make some visual indication of the polarity and meaning of the patterns, and show how the binary encoding changes with flipping and rotating. Andy Smith designed and laser engraved these new caps and locating rings:


The 4 bit binary codes read in clockwise order from the top left (same as the notation for tablet weaving) so rotation causes the same effect as bitwise rotate in programming – multiply/divide by 2 with overflow. There are 4 possible different configurations of magnets (which can provide block identification). Two of the configurations are mirrored on both sides but you can read rotation still, with the other two you also can tell which side is up, and one – bottom left in the photo below, can represent 8 states all by itself (flip as well as rotate).

In future we’ll make more of these with specific meanings dependant on the language we use them for and what they actually do – at this point they are for debugging/experimenting further.


Pattern matrix – putting it together

Here is a member of staff at Miners Court trying some tangible weave coding in the midst of our crafts area – at the moment it’s simply displaying the weave structure on the simulated warp weighed loom with a single colour each for warp and weft threads, the next thing is to get ‘colour & weave’ patterns working.


The pattern matrix is the second generation of tangible programming device from the weavecoding project. It’s been built as an open hardware project in collaboration with Falmouth University’s Makernow fablab, who have designed and built the chassis using many 3D printed parts and assembled the electronics using surface mount components (far beyond my stripboard skills).

Here you can see the aluminium framework supporting the AVR based row controller boards with the Raspberry Pi in the corner. The hall effect sensors detect magnetic fields – this picture was taken before any of the wiring was started.


The row controllers are designed to read the sensor data and dispatch it to the Raspberry Pi using i2c serial communication running on their atmega328 processors. This design was arrived at after the experience of building flotsam which centralised all of the logic in the Raspberry Pi, resulting in lots of wiring required to collect the 128 bits of information and pass it to the GPIO port on the Pi. Using i2c has the advantage that you only need two wires to communicate everything, processing can be distributed and it can be far more modular and extendible in future. In fact we plan to try different sensors and configurations – so this is a great platform for experimenting with tangible programming.

This video shows the current operation of the sensors and row controllers, I’ve programmed the board with test code that displays the state of the magnetic field with the status LED, making sure that it can tell the orientation of the programming block:

The row controllers have a set of multiplexers that allow you to choose between 20 sensor inputs all routed to an analogue pin on the AVR. We’re just using digital here, but it means we can try totally different combinations of sensors without changing the rest of the hardware.

After getting the first couple of rows working and testing it with elderly people at our Miners Court residency there were a couple of issues. Firstly the magnets were really strong, and I worried about leaving it unattended with the programming blocks snapping together so violently (as we plan to use it in museum settings as well as at Miners Court). The other problem was that even with strong magnets, the placement of the blocks needed to be very precise. This is probably to do with the shape of the magnets, and the fact that the fields bend around them and reverse quite short distances from their edges.

To fix these bugs it was a fairly simple matter to take the blocks apart, remove 2 of the 3 magnets and add some rings to guide placement over the sensors properly:


Future Thinking for Social Living: Weavecoding in assisted housing

Our work on weavecoding is now reaching out to other uses and projects. One is Future Thinking for Social Living, run by Magda Ty┼╝lik-Carver and Fiona Hackney.

This research project aims to look at the relationship between wellbeing, home, making and technology and is centred on Miners Court, who provide assisted housing in Redruth in Cornwall. As well as a range of flats and accommodation, the residents have shared communal areas with a variety of activities throughout the week. Along with Christiane Berghoff, Robin Hawes and Lucie Hernandez we set up camp with a lot of materials for knitting, crochet and weaving as well as some Raspberry Pis and the all new pattern matrix tangible weavecoding device.


The Future Thinking for Social Living project is set up to research how we can think more critically about home and community, and with particular focus on the future. From discussions with the staff at Miners Court – specific issues they are interested in are how to make better use of communal spaces, and how can they get more men involved with crafts and shared activities.

I’m also interested in how we can use these settings for artists residencies – how does working with people like this affect a design process, does working in such a place – and using it as way to start conversations (rather than being too much in ‘teacher mode’) affect the people living there positively? Also the weavecoding project provides some ideas in bridging gaps, both between technology and people – but also across gender gaps, mixing textiles with electronics for example.

Here is the new magnetic pattern matrix, running the 3D Raspberry Pi warp weighted loom simulation (more on this soon!) with a nice 4 shaft loom in the background.

On Monday and Tuesday we spent a long time talking, weaving, knitting and making cups of tea of course (and a bit of time debugging magnets on my part). I’ve found helping people weave with tablets on the inkle loom is a good way to get talking, as this seems new to even people who are experienced with crafts. It also appeals to people with mathematics or design background who normally are uninterested in knitting and other crafts, and seems gender neutral perhaps for the same reasons. It also helps to talk about the history of what we are weaving with, the fact that this is an ancient technique and yet there are so many surprises – I can’t really predict to them what will happen e.g. to the pattern when we change rotation direction, and this seems to be important.

What we have yet to do (but a few weeks to experiment yet) is bridge the technology gap. Many of them have an immediate reaction of distaste to computers, as most of them have them but report that they have become unusable or feel that they are not designed well with their needs in mind. Partly the situation of having some circuit boards getting tangled up in the more familiar materials and using the Raspberry Pi simulation to show what is happening on the loom next to it is a start. One interesting thing is that neither the Pi nor the AVR boards look enough like ‘a computer’ for it to stand out too much (which also part of the Pi’s role in the classroom) – this was more so after plugging it into their large TV and getting rid of the monitor. As it gradually gets into a working state, I’d like to first try using it to demonstrate well known weaves – e.g. plain, twill and satin.

Working in this environment on the pattern matrix between weaving with different people has already had an effect on it’s design process. One initial observation resulted in reducing the magnet strength – I hadn’t even considered before that having them snap together too forcefully would be a problem for some people. Such things are obvious in these kinds of settings.

Screenless music livecoding

Programming music with flotsam – for the first time, it’s truly screen-less livecoding. All the synthesis is done on the Raspberry Pi too (raspbian release in the works). One of the surprising things I find with tangible programming is the enforced scarcity of tokens, having to move them around provides a situation that is good to play around with, in contrast to being able to simply type more stuff into a text document.

The programming language is pretty simple and similar to the yarn sequence language from the weavecoding project. The board layout consist of 4 rows of 8 possible tokens. Each row represents a single l-system rule:

Rule A: o o o o o o o o
Rule B: o o o o o o o o
Rule C: o o o o o o o o
Rule D: o o o o o o o o

The tokens themselves consist of 13 possible values:

a,b,c,d : The 'note on' triggers for 4 synth patches
. : Rest one beat
+,- : Change current pitch
<,> : Change current synth patch set
A,B,C,D : 'Jump to' rule (can be self-referential)
No-token: Ends the current rule

The setup currently runs to a maximum depth of 8 generations – so a rule referring to itself expands 8 times. A single rule ‘A’ such as ‘+ b A - c A ‘ expands to this sequence (the first 100 symbols of it anyway):


I’m still working on how best to encode musical structures this way, as it needs a bit more expression – something to try is running them in parallel so you can have different sequences at the same time. With a bit more tweaking (and with upcoming hardware improvements) the eventual plan is to use this on some kid’s programming teaching projects.