GMU:Sensor Hacklab/Christian Doeller: Difference between revisions

I am interested in exploring different ways of interaction between humans and their everyday environment of things.<br>

I want to create a carpet / a collection of carpets that sense people walking on it / them and then trigger a certain output as a response.<br>

I would like to create a complex environment in which people have to move through the space in order to explore its different features.<br>

Therefore I want to explore possibilities of creating an unpredictable output environment.<br>

 

2) creating a simple button matrix / button resistor ladder<br>

3) hacking a toy keyboard + exploring its inner architecture<br>

4) reverse engineering and connecting a keyboard matrix with Arduino + exploring its functions<br>

5) using different matrix systems as a) a resistive sensor and b) a switch based in- and output structure <br>

 

 

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During the first hours we investigated different materials and their conductivity / resistivity.<br>

I was mostly interested in materials that produce variable resistance when they are pushed and squeezed like „resistive plastic foam“.

The outcome is a sensor that reacts to force.<br>

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The first experiment with matrix structures consists of buttons that are connected via a series of resistors. <br>

The last resistor of that kind of „resistor ladder“ ends up in the analog pin of the arduino.<br>,

This way each button evokes a specific value in the analog input reading. <br>

In the second experiment we took apart a toy that included a keyboard matrix to play a collection of sounds. <br><br>

 

We traced each tone on the matrix and soldered external wires to the sound terminals. <br>

This allowed us to access the sounds by using another switching concept in order to trigger each sound.<br>

We chose relays as our main switches and connected them to the sound device.<br>

The relays were connected to the arduino and we were able to trigger and cut off single sound files coming out of the toy electronics.<br><br>

I then decided to explore the matrix of the toy keyboard a little further. <br>

A drawing helped me to understand and trace the switches of each bottom connector. <br>

I then attached an extension in order to access the bottom connectors. <br><br>

'''3) hacking a toy keyboard, triggering it with relays + exploring its inner architecture'''  

I „reverse engineered“ the matrix structure (hidden in the case) after I soldered pin headers to its connectors in order to plug it into the bread board.<br>

<br>

I was mostly interested in using the matrix as a variable resistor rather than using it as a „multiple digital pin input device“.<br>

I achieved that by connecting different resistor values in between each contact of the vertical and the horizontal button lines. <br>

In the end a voltage divider helped to create different voltage changes for the arduinos analog input.<br>

The matrix is actually meant to be used as a "multiple digital pin input / output interface" like shown on [http://pcbheaven.com/wikipages/How_Key_Matrices_Works/ this website].<br>

<br><br>

This way every button represents a certain value in the analog input of the arduino.<br>

By doing that I discovered a major problem: some of the values almost overlapped. In addition to the arduinos analog input pin generated quite some noise.<br>

Therefore I had to define a certain range of values for each button. Although this worked a bit better there was still a lot of overlap.<br>

This overlap sometimes lead to the effect that the interpretation of buttons being pressed was wrong.<br>

<br>

It surprisingly worked out quite well - despite the mentioned overlap problem and the face that I needed a lot of memory. <br>

The overlap problem could be solved by using binary functions / average measurements that define clearer value states.<br><br>

'''5) using different matrix systems as a) a resistive sensor and b) a switch based in- and output structure'''

My hacked version of the toy keyboard does not really work as a system of clear state switches as I rather used a resistive than a conductive material in order to access the matrix (graphite lines). <br>

The multimeter shows that - if I combine all the vertically and all the horizontally connected „lines“ together - I get a certain value of resistance for each button.<br><br>

This way it is possible to use the matrix for instance as a variable resistor for an astable 555 timer chip between pin 6 and pin 7:<br><br>

VIDEO<br><br>

'''6) trying out different ways of implementing switches in a carpet'''

 

The initial idea is to use an anti-sliding mat as a grid that separates the contacts of the switches.<br>

 

Another problem is the material that is used to build the switches.<br>

It needs to be 1) flexible (coming back into its original form) and 2) conductive. <br>

It turned out that a piece of cardboard covered with aluminium foil is the best way to fulfill both goals. <br>

<br>

I also discovered that the size of the gaps inside the flexible grid plays a big role in connection to the performance of the „cardboard-alu switches“. <br>

I tried out different sizes until I found a size that fit to the average „size of a footstep“.<br><br>

[[File:carpet_grid_sw1.JPG]]<br><br>

[[File:carpet_switch_final.jpg]]<br><br>