O-mat

Intro: O-mat

Have you ever wanted to make a giant trackpad? With this tutorial you can make any size of trackpad/force-pad and test it with the included software demo.

We are ONIRIA, we create content, design hardware and develop software to erase the limits of reality and immersive technology.

In the search of full immersion for the virtual experiences we create, O-mat was born. O-mat is an interactive mat that recognizes steps. It is built with 225 (a 15 by 15 matrix array) pressure sensors made of a special material called velostat. This material changes its resistance when pressure is applied to it. We designed an Arduino shield so it could be easy to use, scalable and open platform (coming soon).

STEP 1: The Materials and Tools

For making the mat:

Materials:

• Velostat
• Copper tape
• Any type of insulating fabric.
• Ribbon Cable
• Solder Leaded
• Break Away Headers

Tools:

• Ruler
• Measuring tape
• Cutter
• Glue
• Crayon/marker
• Soldering Iron
• Multimeter

For making the circuit:

Materials:

• 2 Multiplexers
• 1 breadboard
• 1 arduino, for this case we use a mini pro
• 2 leds
• 16 1k [ohm] ressitors
• 2 220 [ohm] resistors

Tools:

• Wire strippers
• Diagonal cutters

STEP 2: For the Mat - Part 1

Use this Youtube video as a guide.

The key component that makes O-mat work is the velostat. When pressure is applied to it, the velostat changes its resistance. Like you saw in the video, we are creating a matrix sensor, specifically a 15 by 15 sensor matrix (225 sensors!).

STEP 3: For the Mat - Part 2

Summing up, you will end having two sides of the mat, one with copper columns and one with copper rows. You will need to weld one by one (I recommend using a ribbon cable for ease of use). You will need to insert the velostat between the to sides of the mat. To finish, you will need to paste both sides of the mat and you are ready to start the circuit.

If you want to make a quick test, with te help of a multimeter, sense one of the pins of the ribbon cable connected to the copper rows of the mat with one of the pins of the ribbon cable connected to the copper columns of the mat. Apply some weight to the mat and see if the resistance changes, if you don´t see that the resistance changes apply weight in other area. If still you don´t detect a change in the resistance check that you make a good welding in the copper areas and the velostat is between.

STEP 4: For the Circuit

Use as guidance the circuit diagrams that are above.

When you finish connecting all the parts in your breadboard, connect the two cables of the mat, it doesn't matter the orientation or the order.

We have just designed the arduino shield, If you want one, you can contact us in our web page!

STEP 5: Connect It to the Computer

All right! At this point you should have something like the image above (the mat with the circuit).

Lets connect the arduino with the computer, if you're using an arduino mini pro, remember that you need an FTDI!

You will need to have the arduino IDE and processing.

STEP 6: The Code - Arduino Sketch

Before you upload the arduino sketch to the micro-controller, check that the pins are connected as the first lines of the code.

Below is the configuration for the arduino mini pro as the circuit diagram that is in the previous step, this configuration is the default configuration in the arduino sketch

//Mux control pins for analog signal (SIG_pin) default for arduino mini pro
const byte s0 = 13; 
const byte s1 = 12; 
const byte s2 = 11; 
const byte s3 = 10;
//Mux control pins for Output signal (OUT_pin) default for arduino mini pro 
const byte w0 = 9;  
const byte w1 = 8; 
const byte w2 = 7; 
const byte w3 = 6;
//Mux in "SIG" pin default for arduino mini pro  
const byte SIG_pin = 0; 
//Mux out "SIG" pin default for arduino mini pro 
const byte OUT_pin = 5;
//Status and Column pins default for arduino mini pro 
const byte STATUS_pin = 3; 
const byte COL_pin = 2;

If you decided to make the circuit with an arduino uno, the configuration of the pins must be like the code bellow

//Mux control pins for analog signal (SIG_pin) default for arduino mini pro
const byte s0 = A4; 
const byte s1 = A3; 
const byte s2 = A2; 
const byte s3 = A1;
//Mux control pins for Output signal (OUT_pin) default for arduino mini pro 
const byte w0 = 6;  
const byte w1 = 5; 
const byte w2 = 4; 
const byte w3 = 3;
//Mux in "SIG" pin default for arduino mini pro  
const byte SIG_pin = 0; 
//Mux out "SIG" pin default for arduino mini pro 
const byte OUT_pin = 2;
//Status and Column pins default for arduino mini pro 
const byte STATUS_pin = 8; 
const byte COL_pin = 9;

STEP 7: The Code - Processing

For the processing code, you will have to change only one number. You will have to change the number inside of the Serial.list()[numbertochange]. Without changing anything in the processing code, try to run the code, in the console window you will see the list of the serial ports, identify the arduino serial port and use that number for modifying in the following line:

myPort = new Serial(this, Serial.list()[0], 115200);

In mi case i found that I have it to change it to

myPort = new Serial(this, Serial.list()[5], 115200);

STEP 8: Play With It!

If you starting to see that the one of the leds starts blinking and you saw a screen like the one above, you have made it. You can start playing with your new O-mat!

Congratulations!!

Comments

[kms50067]

Thank you for the picture of the circuit diagram with Arduino Uno. How can I connect to the breadboard.. It is difficult

[parmthanadol]

I don't know what the problem is.

[parmthanadol]

it's not show.Myport is COM8.

[aris.subril]

Dear ONIRIA. is this velostat pressure sensor is piezoresistive type sensor?

[Waqas_Wani]

yes

[psws1218]

Hi nice work. I made it like you. However I'd like to make sensor matrix 5x5. Could you give me some tips on the code which is changing?

[sibiraj.17]

I would like to disiplay on my computer something like a heat-map when standing on the mat. It shall show you where the pressure is the highest (red) and the are where it is not so high (green-yellow). Do someone of you here have any ideas on how to change the arduino sketch or how to make this work? Would appreciate any help so much. Thank you so far!

[maikel.stawarczyk]

I would like to disiplay on my computer something like a heat-map when standing on the mat. It shall show you where the pressure is the highest (red) and the are where it is not so high (green-yellow). Do someone of you here have any ideas on how to change the arduino sketch or how to make this work? Would appreciate any help so much. Thank you so far!

Cheers

[sibiraj.17]

Hi maikel.stawarczyk, me too looking for the same. are you able to figure it out?

[ajayiitb]

Hello dear mam/sir,

I need your help
can you tell which software you used to see the heat map?

[marc.benington]

Hi Oniria,
Short question: instead of using 16 resistors on C0-15, could you use 1 single resistor on the SIG pin ?
Best regards,
Marc

[marc.benington]

Having searched deeper, I now understand why: the Analog Switch are not ideal (like a relay) but have an internal resistor (70Ohm(typ) @4.5V). This means:
- on the right multiplexer (high side) that the 70Ohm resistance will have to be taken into account in the calculation.
- on the left multiplexer (low side), it is good to have the several resistors as now, so that almost no current goes through the multiplexer (as it is connected to the ADC of the microcontroller). It would be an error to replace these 16 resistors with 1 on the SIG pin, as the 70ohm resistance would also here enter into the calculation.

[panarowi]

Hi Oniria
Thanks for this nice tutorial.
I made the sensor for a sound design project and it works well.
I'm using Max/MSP and machine learning to play with sound in real time.
I
realized that the values are always jumping between 0 and the actual
value (e.g 180 - 0 - 180 - 0 - 180 - 0 ... instead of just keeping 180).
This is annoying because it adds a lot of complexity in datas and make every mapped parameter jump as well.
I'm pretty sure the issue comes from the Arduino code but can't find where exactly (not a pro in Arduino programming...).
Do you have any idea to fix this?
Thanks!

[adamcbrz]

The Arduino code is clamping the values so you can adjust that code to get the raw value if need.

I added comments to help explain the code.

[jdestoesta]

Hi ONIRIA! Wanted to ask what's the importance of the arduino sketch (omat.ino)?

[KvdL.]

Dear ONIRIA, I have an annoying problem: I built the mat exactly according to the instructions (with an Arduino Uno instead of a Mini Pro). Everything seemed to be working just fine, but the places that are pushed on the mat don't correspond with the image feedback in processing. The wires are not corrected incorrectly, so I think it has something to do with the communication between Arduino and Processing. Also, every time I reset the Arduino Uno, the grid changes again: making a different part of the grid "grow" when I am pressing the same place on the mat. Do you have any ideas on how to solve this issue? Thanks!

[OniriaMX]

Hi!

Do you change the code in the arduino changing the order for the mux pins?

Or Maybe It is an error in the sync with all the values with processing, modify the 101 line of processing:

Change from this:

if (serialCount > 224 )

To this

if (serialCount >= 224 )

Cheers!

[Carlospilotfish]

Dear Oniria, I am in the exactly same situation as KvdL. I impletented the change you told but it is not solved, as before, when I press I get a different result every time, and now, it moves creating waves. Please, could you help me?

[rajirk]

i want know about velostat how much weight upto used?

[bogacki.mike]

Great video, I don’t have the knowledge base to make one of these. Can anyone tell me where I could buy pre-made pads or what to search for so I can purchase these mats? Thank you!