This project is a collaboration between Irene Posch & Ebru Kurbak (Stitching Worlds) and Mika Satomi & Hannah Perner-Wilson (KOBAKANT).

>> Tools We Want

Flickr Set:

2014

The content of this website is the outcome of a collaboration between Irene Posch & Ebru Kurbak (Stitching Worlds) and Mika Satomi & Hannah Perner-Wilson (KOBAKANT). Starting in November 2014 and continuing indefinitely. The collaboration is motivated by a joint practice in electronic textiles (or textile electronics) and the desire to try and imagine, design and build functional tools for ourselves.

>> Tools We Want

>>

Links:

Flickr set >> https://www.flickr.com/photos/plusea/sets/72157648904843592/
DIY Cellphone >> http://web.media.mit.edu/~mellis/cellphone/

Notes for improvements…

– have analog counter for number of unread messages (turning bead with numbers written on it)
>> http://www.meggrant.com/movementstudies.php
– much longer battery life

Notes on use…

– does not store SMS
– does not let me read last line of sms
– does not show phone entries for calling numbers or sms
– not very loud ring melody (possibly because no case/resonant body)
– makes no sound when receives sms
– display is shit
– no indication of battery level
– battery life is roughly 1 day, just on (locked), no calling or sms
– time and date not saved if battery dies

Making a leather case…

Links:

>> Sound Hoodie
>> Sound Headband
>> Flickr set

Wireless Charging…

Wireless power >> http://dl.acm.org/citation.cfm?id=2557041
Video >> http://youtu.be/oqtf3zOU1ew

Demo

Video:

Circuit Breakouts (flex and fabric)

Circuit dimensions, outline on tracking paper and scan of final circuit with conductive fabric pads for snaps:

Illustrator layout of fabric PCB, with flex breakout and with all layers:

Top: hacked circuit, Bottom: flex circuit as breakout to fabric breakout

Three layers of flex breakout pcb of hacked circuit to fabric circuit:
– copper with snaps
– double sided tape as mask
– snaps and solder connections showing/poking through to other side

Connections:

– solder connections from copper on flex circuit to hacked circuit
– sewing from conductive thread to snaps on fabric breakout board
– snaps that connect between flex breakout and fabric breakout

Front and back of fabric breakout:

Front and back of hacked circuit with flex breakout board:

Layers of the Knit Design

OUTER, INNER and MIDDLE layers:

Taking apart the Bluetooth Speakers

Bitlace are needle lace motifs that incorporate digital electronics to carry meanings of their own.

for Richard (FOMO)

The name of the motif “for Richard” remains from the relationship within which it was first gifted. Richard’s girlfriend began decorating the hems of his shirt pocket with this Bitlace motif. Friends and family were fascinated by the needlework, and when pressed for her motivations, his girlfriend confessed to them her wish that Richard spend less time keeping up with the world through his devices.

Message: The motif, when applied to one’s own attire is interpreted as a desire to regain control over the technologies one relies on in everyday life. This person might be stressed, overworked or simply overwhelmed by the amount of unread emails in their inbox. When gifted to a close friend or relative, this motif can be read by the recipient as a subtle hint to look up from their smart phone, disengage from the network, and arrive at a style of communication that is more tangible and local.
Motif: a mountain with something hidden on the other side. the person who is scared of missing out can not resist to see what it is on the other side and touching it causes one bit of digital memory to flip state. the circuit of the motif represents one bit of digital memory, depicting the simplicity behind modern forms of communication, zero/one, on/off.
Circuit: The motif “for Richard” represents one bit of digital memory, depicting the simplicity behind modern forms of communication, zero/one, on/off.

>> Bitlace for Richard Swatch Page

Circuit and schematic:

Video

Flipside Flip-Dot

Message: Look on the bright side
Motif: Two sided coin
Circuit: Diode motor/flipdot

Circuit and schematic:

It Takes Two To Tango

Message: Suggests that it takes two willing people to commit an infidelity, not just one
Motifs: Rabbit ears, flower and bee, stick and hole, male/female….
Circuit: Tilt sensor contact switches with vibration motor feedback

Circuit and schematic:

for Andy (Digital Naturalism)

Message: Nature and digital culture don’t clash, they can live side by side in perfect harmony
Motifs: Something with both natural and digital materials/elements/parts
Circuit: Non-functional electronics

Don’t Resist (Change)

Message: Be open to things happening. don’t be so uptight. relax.
Motifs: Open vessels, windows, doors, stretches of grass that change colour…
Circuit: Resistor with thermochromic colour change, or high resistor that decreases in resistance when pressured (led becomes brighter…)

Reminders To Self

Message: Placeholders for messages one wants to remind oneself of every time one interacts with them. they are functional electronic elements that are not hooked up to a circuit. interacting with them does not have any electrical effect – the trigger happens in you.
Motifs: Contact switches and resistive sensors without functioning circuitry
Circuit:

Don’t Panic

Message: Don’t panic, relax
Motifs: Big red pushbutton that does nothing (or does something…)
Circuit: Could light up red LED or sound alarm

Links:

>> CTS Therapy Gauntlet V1
>> CTS Therapy Gauntlet V2
Related project: e-textile sensing glove
>> Code on GitHub
>> Circuit on GitHub
>> Flickr set

Fix

Problem: Bad connection(s) causing misbehavior. Speaker does not always work…

From examining the stulpe circuit, the failure comes from the fact that plugging and unplugging the FTDI or Bluetooth module is exerting too much strain on the edge pins of the 6-pin header. These edge pins represent the GND connection and the SCK connection. GND is vital and has been repaired. SCK still remains somewhat in tact and is only relevant for re-programming which can also be done via the SMD chip clip (which i would recommend anyway).

GND connection fixed by peeling back some of the soldermask and enlarging the solder area to overlap the probably crack in copper.

Area of reinforcement to the back of the microcontroller and 6-pin header area so that strain is relieved from solder joints in this area. Plus, when bent the bend does not happen at solder points. This reinforcement is standard in flex PCBs and probably a good thing to add to future editions of this design.

Final Version Documentation

SUGGESTIONS for improvement of current implementation:
– Program circuits to trigger alarm if EITHER sensor is past threshold for given time-limit.
– Mark on/off of switch somewhere on circuit
– Re-make stulpe with knit sensors in ranges under 500K Ohm, so that skin resistance does not interfere

Photos

ATtiny microcontroller with programming headers:

Speaker, LED, Snap connector and Slide-Switch:

1uF filter capacitor (left), 1M Ohm pull-up resistor (right) on each sensor input:

Battery pouch can hold one or two 3V coin-cells:

Parts

– ATtiny85V (this version of the chip can run at lower voltages: 0 – 4 MHz @ 1.8 – 5.5V, 0 – 10 MHz @ 2.7 – 5.5V)
see datasheet >> http://www.atmel.com/images/atmel-2586-avr-8-bit-microcontroller-attiny25-attiny45-attiny85_datasheet.pdf
– SMD LED
– Speaker
– Resistor
– Capacitor
– 6-pin header
– Slide switch
– Snaps
– 3V coin-cell (CR2032)
– Knit sensors (see bellow)

Knit Sensors

Knit from XXX yarn. The ranges of the variable resistance knit sensors vary. They were measured to be between 8M Ohm (fully relaxed) and 500K Ohm (fully stretched/compressed on wrist) 10K Ohm (fully stretched off wrist). After some use the range generally shifts down to around 2M Ohm – 600K Ohm. Though this may vary again over time. Based on the measured ranges of the knit sensors, 1M Ohm pull-up resistors were chosen for the voltage dividers.

It is almost impossible to trigger the top sensor without triggering the bottom sensor.

Circuit

The final circuit is designed in Eagle, although the size of it exceeds the board space provided by the free Eagle version, so that components are confined to limited area. An elongated variation of the final circuit allows for the circuit to wrap around and fit a larger variety of wrist circumferences. This elongation of the circuit was done in Illustrator. The final circuits were etched at the TU from one-sided copper plated Kapton film. The soldermask is lasercut from black silk fabric with fusible adhesive backing.
>> Circuit on GitHub
Etched circuits and soldermask:

Arduino Code

>> Code on GitHub
The Arduino code is the same for both circuits and incorporates both stand-alone and Serial modes. Meaning the sensor values are always being sent over the soft Serial port regardless whether they are being received on the other end. Because of the huge variation in sensor ranges, the thresholds for each Stulpe will likely need to be adjusted regularly.

Stand-Alone Circuit Behavior:
When the circuit powers up the speaker sounds short beep tone and the LED light fades on and off to indicate the circuit has come on and both outputs are functional.

If the TOP sensor is past it’s threshold the LED will blink slowly. If the BOTTOM sensor is past it’s threshold the LED will blink fast. If both sensors are over their thresholds the LED will be on. If both thresholds are exceeded for over 200 cycles (roughly 10 seconds) then the speaker will sound the beep alarm until one or both sensors fall back passed their threshold.

In summary:
TOP –> blink slow
BOTTOM –> blink fast
BOTH –> always on
BOTH && TIME –> beep and blink

The LED is connected to a PWM pin so that it’s brightness can be dimmed if it is too bright to look at.
analogWrite(ledPin, [0-266]);

Serial Circuit Behavior:
(same as above with the addition of the following:)
The ATtiny is constantly transmitting the following comma-separated-value message over it’s soft Serial port: “TOPsensorValue[0-1023], BOTTOMsensorValue[0-1023], state[0-4]”, where state values mean the following:
0 = neither sensor value has past threshold
1 = TOP sensor value is past threshold
2 = BOTTOM sensor value is past threshold
3 = BOTH sensor values are past their thresholds
4 = both sensor values have past threshold for long enough and alarm is sounding

Screen-shot of Serial COM:

Processing Sketch

>> Code on GitHub
The processing sketch reads the Serial message and graphs the first two values. If the value of a sensor is passed it’s threshold the graph line will be drawn red, else black.

Screen-shot of Processing graph:

Re-Programming

CAUTION: when powering the circuit over the 6 pin header connection (for example via FTDI) make sure the power switch is turned OFF. If the battery is left in the pouch then the 5V USB + 3V battery power will be too much for the circuit! If the battery is not in the pouch the + and – of the battery connections are shorted inside the pouch! Alternatively you can insert a non-conductive spacer into the pouch to separate the + and – connections.

To re-program the ATtiny on the Stulpe circuit the easiest way is to make a custom ISP connector that will plug directly on to the 6 pin header. The 1uF capacitor on pin2 needs to be removed before programming.

Diagram of custom connections, photo of connector/adapter:

Serial COM vs. programming connections:

Differences Between Circuits

The two final circuits (marked A and B) are the same in all respects, except:
– Circuit A has 6 pin header pins soldered to flex pcb for easy programming and FTID/Bluetooth connection, and B does not have this header pin attached.
– Circuit A and B have different on/off switches: A has upward facing, B has sidewards facing.
– Circuit A is paired with Stulpe yellow. Circuit B is paired with Stulpe pink.

FTDI Serial Connection

The TX pin of the serial connection interferes with the analog reading of the bottom sensor connected to pin 2 (ADC1), which is wired to the 6 pin connector for programming because pin 2 is also SCK. The following adapter only makes the necessary connections for the one-way Serial communication that the Stulpe circuit uses (VCC, GND and TX).

Bluetooth Serial Connection

Use same adapter as for FTDI board. I could not get the UdK Bluetooth module to pair with my computer! Does it have a different pairing code than the default 1234?

Circuit A

Circuit B

For the Future

Improvements for Future Iterations

– Knit sensors should be lower resistance (KOhm – Ohm) so as not to come close to skin resistance range (1-2MOhm)
– Knit structure should be optimized for more consistent sensor values. Partial elastication could allow for pre-stretched material and tighter fit. Ribbing could allow for greater range of yarn deformation when pressured/bent/stretched
– Jumper connections under soldermask
– Placement of top sensor (pin3) pull-up resistor and capacitor not so close to speaker footprint
– Center battery pouch on underside of wrist
– Recede header pins so that they don’t stick out

Remaining Issues and Workarounds

– Bottom sensor’s capacitor interferes with programming the ATtiny –> has to be removed to re-program chip
– Bottom sensor’s SCK connection to TX on FTDI board interferes with reading analog value (pulls it high) –> workarounds: (1) cut TX connection on FTDI, (2) use adapter that skips TX pin, (3) find a way of setting TX pin on FTDI board to be neither high, nor low, (4) check possibility of switching current SCK and RST pins on custom 6-pin header (could result in other implications…)

ASCI CIRCUIT DIAGRAM

///////// CIRCUIT DIAGRAM /////////
// _______
// RST –|° |– VCC
// BOTsen/3 –| |– 2/ADC1/TOPsen/SCK
// SPEAK/4 –| |– 1/tx/MISO
// GND –| |– 0/LED/MOSI
// _______
////////////////////////////////////

Updated Circuit

Updates made in this version:

– added toggle switch for programming connection (Pin1 — TX)
– larger pads for larger snaps with holes through both copper and base substrate for males snaps to poke through
– smaller pads for resistors and capacitors
– smaller soldermask window for ATtiny
– single-colour LED
– smaller speaker/buzzer
– remove snap power switch and include toggle power switch

Final updates made in Illustrator to lengthen ends to allow for different wrist sizes and for the circuit to wrap around and close on itself, rather than on the knit fabric.

Schematic and layout in Eagle:


Cut files traced in Illustrator:

Ideas for power source…

coin cell
– 3 x 1.5V button cells in series (4.5V). using SMD holders like one bellow
– 3V CR927 button cell in SMD holder >> http://de.rs-online.com/web/p/batteriehalter-halterungen/4814178/
– 3V CR2032 coin cell in nice black holder >> https://solarbotics.com/product/BHold2032/
– make own coin cell holder from fabric and magnets
– rechargeable coin cell battery that can be hard wired with charging connections broken out >> http://www.megabatteries.com/item_details2.asp?id=14509&cat_id=469&uid=1718

lipo
– small lipo battery with shortened cable. include charging circuitry on board? or have to unplug to charge? JST connectors are a pain to plug and unplug!
– lipo battery inside pocket inside stulpe and power connections travel from inside to outside through snaps

Option 3) Flexible (flexible and spaced, wraps around wrist)

Instead of grouping parts into hard nodes as in option 1, spread them evenly and space them out over the full circumference of the wrist to keep the circuitboard as flexible as possible. For this option it would be great to have access to a flexible circuit etching facility.

Issues with previous version:

switching the circuit back and forth between stand-alone and serial-bluetooth modes, the following issues arise with current design.

1) ATtiny Pin1 connected to LED(blue) and is TX connection when doing Serial communication via Bluetooth. LED gets in the way of TX–>RX!
solutions:
– insert toggle switch between LED(blue) and is TX connection – – probably the way to go. but adds extra component
– only use one LED, leaving Pin1 free for TX serial com

2) ATtiny Pin2 and DTR of Serial/Bluetooth connection as this pulls pin low and gets in the way of reading sensor input from Pin2/ADC1!
solutions:
– swap SCK and MOSI connections on 6 pin custom ISP connector so that sensor Pin2 does not connect to DTR of Serial/Bluetooth connection – – good to do anyway (and solves problem)!
– insert toggle switch between Pin2 and DTR connection
– cut DTR connection on bluetooth module as we are not using it and it is in the way

Alternative solutions to both above problems:

– have two separate circuits, one for stand-alone demo, one for serial-bluetooth visualization demo

3) (small issue) battery pouch shorts + and – when there is no battery inside. this is only an issue when operating using separate power supply over ISP connector and closing the full wristband. always leave wrist-band open when connecting power via 6-pin headers.

Hard/soft connections

the hard/soft electrical connections are made with hand-sewable snaps. on the side of the stulpe the snaps are sewn with the remaining conductive thread from the knit sensor leads. on the side of the flex PCB the snap is mounted through a hole from above so that when removing the circuit from the stulpe the forces are not on a connecting thread. this is holding up really well in terms of connection and robustness.
the ordering of connections is altered on the circuitboard. on the stulpe it is: sensor1 – GND – sensor2, on the circuitboard it is: GND – sensor 1 – sensor 2

Battery and holder

current solution is a self-made coin-cell holder made using conductive fabric (+) and a magnet (-). the battery is easy to insert and remove and the connections are good. it also fits with the design. and two coin-cells can be inserted for more power. i could imagine assembling a wireless power module with lipo battery into a similar form-factor as the coin-cell battery so that it could sit inside the pouch and make contact the same way. although the consequences of a lipo battery shorting out are much much worse.

Power switch

the power switch for turning the circuit on/off is made by closing the final snap connection next to the battery on the stulpe. the strap anyway has to come off here so that you can put the stulpe over you hand.

Kapton Folien

Müller-Ahlhorn:
>> http://www.mueller-ahlhorn.com/de/produkte-materialien/material/technische-folien/pi-polyimid-folien/
Krempel Group:
>> http://www.krempel-group.com/deutsch/home/produkte/spezialfolien-und-papiere/kapton-polyimidfolien.html
RS:
KAPTON FILM 304X200X0.05MM, 53,10 €
>> http://de.rs-online.com/web/p/warmeisolierende-folien/5363952/
Wärmeisolierfolie Kapton HN PA 304mm x 200mm x 0.075mm, 69,42
>> http://de.rs-online.com/web/p/warmeisolierende-folien/5363968/?origin=PSF_436275|alt

Option 2) Length-Wise (hard and long)

Instead of mounting the 3 snaps around the circumference of the wrist, have them placed in a line running along the wrist. This would allow for a circuitboard design that does not need to flex around the wrist and could be made on hard PCB. For this option it would be nice to have hard pcb manufactured with fritzing.

Option 1) Modules (hard and tiny)

To keep the circuit flexible, parts and functionality are groups into small areas with flexible areas in between. one option is to make the hard nodes from hard PCB material and solder wire connections in between (see photos). Another option would be to design a hybrid circuitboard that transitions between hard and flexible pcb materials. For this option it would be nice to have hard pcb nodes manufactured by fritzing. Their boards are white and most of the electronic parts are black. The black/white aesthetic would go well with the colours of the stulpe.

Modules…

Module string

On stulpe

Detaching

Comments and Observations

– In order to attach and remove the circuitboard from the snaps on the stulpe a considerable amount of strain is exerted on both the knit fabric of the stulpe surrounding the snap, as well as the snap mounted on the circuitboard. reinforcement backing added to the knit fabric helps relieve and distribute this strain on the side of the stulpe.
– There are a number of small components on the circuit and if the circuit is made super small then all these small parts end up very close together forming a firm surface, even if they are mounted on flexible circuitboard.
– Machwerk has had to move out of their space so i currently don’t have access to an etching bath. for now my options are vinylcut coppertape or lasercut copper fabric.
– A flexible circuitboard made of copper tape (vinylcut) or copper fabric (lasercut) is very fragile when bent and strained at the solder joints.
– Stulpe knit fabric is not very stretchy or tight fitting so sensors are not stretched/pressured much through bending the wrist up and down. Pressuring of the wrist against the surface of the table is most reliable.

Parts

– Male and female metal snaps
– ATtiny mircorontroller
– RGB LED
– Speaker (or vibration motor) — make the speaker coil directly on the pcb and just add magnet
– 2 Pull-up resistors
– 2 Capacitors
– JST socket
– LiPo battery
– Slide switch
(- Programming pins)

Initial Circuit

Challenge

To design a circuitboard that connects to two knit stretch/pressure sensors embedded in the Stulpe (German for wrist warmer). The circuit should read the values of the resistive sensors, visualize when sensors are triggered (threshold exceeded) with coloured light and sound alarm (speaker beep or vibration motor?) when both sensors are triggered for certain amount of time.

Images of Stulpe in different positions:

One sensor triggered:

Both sensors triggered (TOP, BOTTOM):

Spacing of contacts…

Reinforcement in back…

Links:

>> Photos on Flickr
>> Code on GitHub

Sensors

Test Setup

To test the sensitivities and ranges of the various sensors, an easy way to visualize analog input will be to program the Teensy to appear as a joystick when plugged in, because a joystick HID device has 6 analog inputs. A processing sketch will then graph the values of these 6 analog inputs.
>> https://www.pjrc.com/teensy/td_joystick.html

We can use the following Arduino code:
There are six functions to control the Joystick’s 6 axes. Each takes a number from 0 to 1023, where 512 is the center or resting position.
Joystick.X(value); // “value” is from 0 to 1023
Joystick.Y(value); // 512 is resting position
Joystick.Z(value);
Joystick.Zrotate(value);
Joystick.sliderLeft(value);
Joystick.sliderRight(value);
Joystick.button(num, 1); // Press button “num” (1 to 32)
Joystick.button(num, 0); // Release button “num” (1 to 32)

Download and Install Processing

>> https://processing.org/download/?processing
64 bit download link >> http://download.processing.org/processing-2.2.1-windows64.zip
32 bit download link >> http://download.processing.org/processing-2.2.1-windows32.zip

Open the example Mouse2D

Once installed, to test that processing is working, open up the “Examples” menu, and select the “Basics” –> “Input” –> “Mouse2D” sketch. Run the sketch by pressing the “play” button in the top left corner of the processing screen. A new window should open. Navigate the mouse cursor to this window. As the mouse inters the window space it will start to manipulate the squares.

Transitioning from JoyStick Test Setup to Mouse Setup

When we want to re-program the Teensy from being a Joystick, to being a computer mouse, we’ll need to update the hardware (re-plug new sensors into sockets), and the code on the Teensy.

Re-programming the Teensy

Download and Install the Teensyloader
>> https://www.pjrc.com/teensy/loader.html
windows XP download link >> https://www.pjrc.com/teensy/loader_xp.html
windows 7 and vista download link >> https://www.pjrc.com/teensy/loader_vista.html

Download and Install Arduino
>> http://arduino.cc/en/Main/Software
download link >> http://arduino.googlecode.com/files/arduino-1.0.5-r2-windows.exe
getting started (step 4, install drivers) >> http://arduino.cc/en/Guide/Windows

Download and Install Teensyduino
>> https://www.pjrc.com/teensy/td_download.html
windows installer download link >> https://www.pjrc.com/teensy/td_119/teensyduino.exe

Different Sensors to Test

Simple Fabric Pressure Sensors (eeonyx, velostat)

>> http://www.kobakant.at/DIY/?p=232

Simple Tape Pressure Sensors

>>

Capacitive Sensing

>> http://en.wikipedia.org/wiki/Capacitive_sensing
Capacitive sensing on Teensy >> https://www.pjrc.com/teensy/td_libs_CapacitiveSensor.html

Skin conductance as contact switch

>> http://en.wikipedia.org/wiki/Skin_conductance

Hall Effect Sensor and Neodymium Magnet

One idea would be to mount the magnet on the finger (possibly with nail-varnish to fingernail?) and then measure proximity between sensor and finger with nothing in between. This would also mean no force feedback to the finger to let it know how “hard” it is pressed – how close it is to the sensor.
Another idea is to mount the magnet on one side of a squishy material and the sensor on the other. Distance between magnet and sensor should be chosed to maximize range of sensor’s sensitivity, and squishy material should be chosen to be as easy as possible to “squish” and attain full range of sensor. Squishy material should also maintain it’s ability to recover, and not wear down over time.

>> http://www.digikey.com/product-detail/en/A1324LLHLT-T/620-1402-1-ND/2639992
>> https://www.sparkfun.com/products/9312
with tiny neodymium magnet >> http://www.kjmagnetics.com/proddetail.asp?prod=D11
Arduino tutorial >> http://playground.arduino.cc/Code/HallEffect
Buildr tutorial >> http://bildr.org/2011/04/various-hall-effect-sensors/

Bend Sensor as press sensor

>> http://www.flexpoint.com/companyInfo/bendSensor.htm

Bend Sensor mounted on a finger knuckle
>> http://www.flexpoint.com/companyInfo/bendSensor.htm
>> https://www.sparkfun.com/products/10264

Force Sensing Resistor (FSR)

>> https://www.sparkfun.com/products/9673

Light Barrier Sensor

a light sensor (LDR) and IR LED to create a light barrier that you can break by moving between
>> http://de.rs-online.com/web/p/products/2192533/?cm_mmc=aff-_-de-_-octopart-_-2192533

Whisker Switch

>> http://jmpswitches.com/product/whisker-switch/

Teensy Carrier Board

Circuit diagram:

Photo:

Input from Jussi

To Try:

-add at least double the capacitance of the input filter to VCC (or just put 47uF there, regardless of anything else)
-invert the voltages for the sensor (so that the signal is trying to rise from gnd when pressed)
-use internal 1.1 Vref ( check that there’s a cap and nothing else on the ref-pin ) [ analogReference(INTERNAL); ]
-just a small low-pass for the signal (e.g. 10nF, could try less than what the VREF-pin has. )
That should give a better resolution of the interesting part of signal range without changing anything too much. If the voltage goes over 1v1, and you need to determine it, just change the analogRef to something higher and measure a few more times.

Optional:
-filter the voltage to the sensor (both the sensor and the divider-resistor) with a low-pass -filter (100R + 10uF is more than enough)
-if you can do this for the AVCC, even better
-increase the size of the divider resistor from 1k, makes the conversion a bit faster, although the range might be worse. Faster conversion -> more averaging. Also, for averaging, use samples in power of 2. Math is much faster this way.

The brief peak in the voltage, when pressed and released, might be due to several things. That’s a very interesting dip. It could be that when the pad is pressed, the current draw briefly increases before the USB-cable-combination is able to provide more power. With the low-pass-filtering, the value at the analog-input pin stays stable, as it should. However, since the VCC-voltage dips, the dip goes to the AVCC and AREF respectively, causing the voltages to get a bit lower. Since those are the voltages that set the maximum analog values, if it dips, then the stable inputs will be seen as rising.
To test this: if you press the pad super-slowly, is the dip visible? If you put a smaller filter cap-does the dip become lower? If you put a big filter-cap between VCC-GND, is the dip smaller?

Also, ATtiny85 has differential ADC inputs, with a gain of x20. Unfortunately, mega328p doesn’t. You could also use t85 with adc at x20 setting. That should definitely give the resolution you need, if you use it in combination with the above. Then you could make smart “buttons” of t85, which feed the signals to the whatever arduino you want to use with the software.

Suggested Solutions:

-instrumentation amp + filter -> should get signals out of the current implementation, although I’d also add active shielding (again the electronics inside a conductive envelope, with the envelope being actively driven to a known value.)
*it already gives signals, but those are probably very faint and noisy with very light touches

-thin capacitor sandwiched inside a conductive envelope -> construct an oscillator to measure pF changes
-> very cheap, relatively stable (can be isolated), requires active pulse duration counting from arduino
-> can be very, very flat

-IF the fabric can move at least a bit, a thin magnet and a hall-effect sensor to measure the field strength, by far the easiest to interface with arduino

Questions:

-size requirements? >> see bellow
-what is the distance that the opposing sides of the touchpad can travel? (or should it remain relatively stationary? [as in <0.5mm travel])
*if it should remain stationary, then the measurement is going to be a bit more tricky, but doable
*if it can move a bit, then the distance traveled can be measured, and by proxy, the amount of force exerted on it
-is the expected signal to be linear relating to the pressure or can it be non-linear, or even non-repetitive?
*on a related note, is the expectation on a long-term continuous signal, or just short presses?
-how stable are the hands/fingers of the user in terms of hydration levels and shaking?
-how is the sensor going to be maintained? (washed, cleaned, changed to a new one? / what kinds of dirt)

Further Research on Existing Solutions

A Big Thanks to Edupro for supplying me with a free Ultra Light Switch, which activates at 10 grams.

Two other solutions by Adaptivation that take a similar approach to sensing pressure and triggering a button press are the Pal Pad and the Flexible Switch:
– Pal Pads activate at 34 grams (1.2 ounces) >> http://www.adaptivation.com/product_detail.php?ID=44
– Flexible Switch activates at less than 57 grams (two ounces) >> http://www.adaptivation.com/product_detail.php?ID=50

The Traction Pad looks like does capacitive or skin resistance sensing and activates upon touch (skin contact):
>> http://www.adaptivation.com/product_detail.php?ID=46

First Fabric Pressure Sensor Prototypes

Light Touch Pressure Sensor >> http://www.kobakant.at/DIY/?p=5210

Video

Explaining how sensors aren’t working as good ad i’d like!

Design Update

Design Sketch

– Setup: all fingers rest on the pressure sensors at all time. Pressure sensors are triggered by pushing fingers down. Hand weight does shift a little bit
– Trigger pressure: the easiest switches to activate require 10 grams of force, so anything under 10 grams would be good
– Proposed key-combination for entering calibration mode: holding right click down, double left click and then double click UP
– Size and shape of pressure sensors: rectangle 2 x 3 cm (reference size is average width of finger)
– Thickness of sensors: 6-10 mm

Current Interface Setup

Position of Hands

Arrangement of Buttons

– Placement of pressure sensors:
– – Three of the pressure sensors on top of the 3 existing switches for right hand
– – One pressure sensor under left thumb knuckle
– – One pressure sensor under left middle finger knuckle
– – One pressure sensor under left pinky knuckle

Overview

Current setup:

– Windows operating system
– Stealthswitch AT-10 USB Switch Interface to plug in accessible switches ($79) >> http://www.stealthswitchat.com/
– 3 Ultra Light HD Switches ($20 each) >> http://www.marblesoft.com/store/index.php?route=product/product&product_id=129
– Mousekeys feature in Windows for mousing

Problems:

– The switches are getting to hard to push
– The Stealthswitch AT can only do one key or a command like Control-V per switch and can’t do macros

To Build:

– Use Teensy 2.0 instead of Arduino for analog/digital conversion (has 12 analog pins) and HID (Human Interface Device)
– Device should be seen as a USB Mouse (HID) by any OS
– Six fabric pressure sensors (one for each mouse direction and left and right mouse buttons)
– Individual (and easily adjustable!) resting thresholds for all 6 sensors because “buttons” should not activate because of the weight of resting fingers!
– Cables from the Arduino to the sensors be approximately 1.8 meters long
– Plug connection from pressure sensor cables to Teensy
(- Bluetooth would be cool but not necessary)

To Program:

– Mouse input does not trigger until threshold is exceeded
– The mouse cursor moves faster the harder the pressure sensor is pressed

Questions:

– Size and shape of pressure sensors?
– How to set and adjust thresholds easily/conveniently?
– How to mount pressure sensors? Sticky/reusable backing? Velcro on back of buttons and velcro surface on which to arrange placement of buttons? Mounted on something solid with holes for screw mounting?
– Different colours on surface of buttons for visual differentiation? different textures for tactile differentiation?
– Connections from pressure sensor cables to the Teensy? Pressure sensors should be detachable from Teensy to make replacements/fixes/changes/improvements easy. Should we go with industry standard (3.5mm mini plug and socket) or would header pin connections be okay? Other options?

Details

Teensy

Teensy >> https://www.pjrc.com/store/teensy.html
Handcrafting Textile Mice workshop at DIS >> http://highlowtech.org/?p=378

Pressure Sensors

Pressure Sensor Matrix >> http://www.instructables.com/id/Pressure-Sensor-Matrix/?lang=de
Video >> http://www.youtube.com/embed/3rFb-O64wL8

Thresholding

Whole System:

Materials/Costs

Electronics:
$16 Teensy
$2 long USB mini cable

Fabric materials:
neoprene
conductive thread
conductive fabric
Velostat
EeonTex
copper tape

MISC:
Wire/cables
Connectors
Potentiometers
LEDs for visual feedback on thresholds
Casing for Teensy (Tupperware or nice wood box)
Velcro mounting or similar

>> Swatchbook Exchange Website

The Exchange takes place every year since 2013 as part of the 2013 E-Textile Summercamp in Paillard, France.

Everybody participating in the exchange is either a past or current participant in the Summercamp, and creates as many multiples of their swatch as are participants in the exchange.

2014

>> http://etextile-summercamp.org/swatch-exchange/category/2014/

2013

>> http://etextile-summercamp.org/swatch-exchange/category/2013/

Video:

>> Gloves Documentation

Team: Imogen, Kelly, Tom, Seb, Rachel, Adam, Hannah

Links:

>> MiMu website
>> Dev Blog
>> Kickstarter page
>> Imogen’s Glove Page
>> Making-of x-IMU Gloves
>> Twitter
>> YouTube Videos
>> Flickr Photos
>> Seb’s Glove GitHub

The x-IMU Gloves

This first pair of customized gloves uses custom made version of the x-IMU. Each glove has one x-IMU, 8 bend sensors, an RGB LED and vibration motor.

The DIY ArduIMU Gloves

An Open Hardware pair of datagloves that capture movement and gestures of the hand using the ArduIMU and bend sensors. The gloves can be connected with an FTDI cable or wirelessly using a Bluetooth module. The gloves also include an RGB LED light and a vibration motor for visual and haptic feedback.

These gloves are made from off-the-shelf parts and documented in these step-by-step instructions.

E-Textile Gloves

This is a version of The Gloves that uses conductive and piezoresistive fabrics to capture movement and gestures of the hand in an attempt to build a fully fabric data glove.

MiMu Gloves

Three pairs of this version of the glove were produced in preparation for Imogen’s NIME performance.

Collaborator Gloves

This version of the MiMu data gloves for composing and performing electronic music are in production for a small group of collaborators who continued to support us after our Kickstarter campaign.

>> How To Get What You Want