This is a tutorial on how to make a pressure sensor mat using velostat, a material whose resistance changes when pressure is applied to it. These are a series of prototypes for a larger project I am currently working on, for a large scale pressure mat that will trigger a series of LEDs that will fade or pulse in time with meditative breathing.
Step 1: Materials and Tools
This project is relatively light on tools and materials, which is good, because this is a rapid prototyping project, the materials are also relatively cheap and can be found at most electronics components store and around the house, save the velostat, which I ordered from Adafruit.
- Velostat ($3.95 per square foot on Adafruit)
- Copper Tape
- Thick cardstock
- Masking tape
- Wire, or aligator clips for later testing
- Cork backed metal ruler
- X-acto knife and blades
- wire strippers and cutters
- cutting mat
Step 2: Step 1: Cutting Your Materials
I recommend cutting all your materials at the same time to avoid having to re-cut anything after figuring out your material is the wrong size.
For this prototype I cut two equal pieces of card stock, about the size of my hand.
The copper is cut in two pieces of roughly equal length. Make sure your copper tape is about 4cm longer than the longest side of your card stock, this will allow the copper to be wrapped around the edge of the card stock, providing a purchase for your alligator clips for later testing.
Finally, cut the velostat, I used my x-acto knife with a brand new blade to try and get the cleanest edge possible, this is not vital, but makes your prototypes look better in later documentation. The velostat should be cut so that the card stock makes a visible border on all sides.
Step 3: Step 2: Applying the Copper Tape
When applying the copper tape, try to peal back a small bit of the paper backing at a time, and slowly inch your fingers across the card stock. Not only will this minimize bubbling and kinks in the copper, but it will prevent your copper tape from rolling back onto itself and getting stuck. That sh*t does not come apart once it's stuck to itself.
Start by sticking about 2cm -or half of the overhanging length you left when cutting the copper tape- to the backside of the card stock. Wrap the copper tape around the edge of the card stock, and then inch by inch, apply the copper tape until your left with the remainder of the overhang. Wrap this around the opposite edge you started on, and stick the rest of the tape to the back of the card stock. Repeat on the second piece of card stock.
Lastly, I applied a little bit of masking tape between the two pieces of card stock to act as a living hinge, this will help you keep your pieces in line with each other while testing.
Step 4: Step 3: Adding the Velostat
Tape the velostat in the centre of one of the pieces of card stock. That's it for this step! Easy peasy.
Step 5: That's It!
And there you have it! That's the simplest way I know to make your own pressure mat. Here are a few more prototypes I've done.
Try playing around with the placement of the wires, the copper or even how much velostat you're using.
Step 6: Bonus Step:
This is the set up I've been using to test my PWM for the LEDs. The set up was found at this link here:
The circuit diagram was provided by fritzing, but I basically just recopied the one in the link. The push button is being used as a subsitute for the pressure mat while I workout the code, which is a combination of PWM, state change detection and later integrating the pressure sensor with an If Statement. All these codes can be found on the main Arduino site.
Special thanks to Garnett, Bobbi and of course the helpful guys at Lee's Electronics!