This was what I worked with. An unassuming black sheen. On first impression, I thought, “So… non-coloured coloring paper?” (black is not a color, as we learnt in school :nerd-emoji: ). If first impressions were ever to last, I would never have learnt of its capabilities in tinkering, let alone that it has a name as cool as The Velostat. But alas, they almost never do! As it turned out, a Nanyang Polytechnic (NYP) project recently taken up by the company was the perfect opportunity to experiment with and flaunt the Velostat’s electrical properties.
The Velostat
At its core, the Velostat is a simple material - it is a pressure-sensitive conductive sheet. Its resistance comes from the fact that it is carbon impregnated black polyethylene. The more pressure is applied on it, the less resistant to electricity it becomes. When sandwiched between two conductive layers, it offers a great range of electrical resistance. This makes it a superb variable resistor, which is a critical component for the company’s upcoming NYP project with a singular goal: create our very own Dance Dance Revolution Arcade Step Machine!
“When pressured is applied, the velostat’s electrical resistance decreases.”
The variable resistor I speak of here refers to the four Step Devices (arrows printed on them). Here is a quick mock-up of a single variable resistor:
The Step Device is a Variable Resistor Unit
The variable resistor unit (left-hand side) has a simple concept. It consists of two black velostat sheets, sandwiched between two pieces of felt. Conductive copper strips are taped on the inward-facing surface of the two felts (represented by the hashed inner felt surface). To form a unit, the three sides of the “sandwich” not to be connected to wires are taped together. Here’s a look at our first milestone!
Linking to the microcontroller
Following that, a stripped wire connected to the VCC (or Power Source Pin) is soldered onto the copper strip on the top felt, while another stripped wire, connected to both the Analog Pin and the Ground Pin, is soldered onto the copper strip on the bottom felt. All three Pins are located on our Freaduino microcontroller (this would also work with an Arduino Uno) powered by a computer.
Quadruplicate!
A single step device won’t do! I need four step devices connected to microcontroller to really make our creation work. Despite the wire-y mess, completing this step was particularly satisfying – it’s started to vaguely resemble to Step Machine!
Ah, now do you see the critical importance of the pressure-sensitive conductive sheet – the velostat - in this setup? Yes, stepping onto a single step device reduces the velostat’s electrical resistance! And purely by Ohm’s Law, (V = IR), we know that as the velostat’s resistance decreases, the electrical current passing through it increases, and this reading can be read off of the Analog Pin on the central microcontroller. Perfecto!
Code
Now, I won’t get into the nitty gritty details of the code. After all, our CEO Akmal was the code writer (much thanks!). But here’s how the software supplements the hardware:
- Before being stepped on, all four Step Devices – A, B, C and D – are of the state Unstepped or A0, B0, C0 and D0 respectively
- Say, Step Device A is being stepped on, its resistance decreases and the current passing through it, as read off the Analog Pin, increases.
- Past a specific current threshold value on the Analog Pin, Step Device A’s state changes to Stepped or A1.
- Different combinations of 1’s on different Step Devices will trigger different responses on User Interface displayed on a linked TV Device. Examples:
- A1 B1 C1 plays an educational video on the TV.
- C1 B1 A1 initiates an exciting game to be displayed.
- D1 A1 B1 plays the “Never Gonna Give You Up” music video on the TV.
Viola! Now, we simply wait for an unassuming participant to be rickrolled (just kidding… or am I?)
Challenges I Faced with the Velostat
By running the Arduino code and printing the analog readings, I found that for one of the Step Devices, the electric current running through it exceeded the threshold value even without being stepped on. Hmm… the code was alright, it passed all our tests. All other Step Devices seemed to be running fine even after switching wires around and replacing copper tapes. As a budding maker myself, I was extremely frustrated as I went around debugging the device, going through the list of possibilities of what could have went wrong. Gah!!!!
As it turned out, the excessive solder I used, combined with the tight surrounding tape, created pressure that would have already reduced the velostat’s resistance even before external pressure was applied.
To remedy this, I made use of four long strips of paper and slotted them in between the two sheets of velostat within all four variable resistor units. This made sure that at least for the sides of the velostat sheet, any slight additional pressure created, whether from the tight external tape or potentially excessive solder, would not inadvertently and excessively reduce its electrical resistance from the get-go.
Well, it appears to me that the Velostat really is fairly sensitive to any changes in pressure. This fair sensitivity means that you do have to be extra careful not to unintentionally create any excessive pressure within your creation, so as not to reduce the velostat’s electrical resistance from the start.
TLDR
The velostat is fairly sensitive to pressure! Please do take caution not to unintentionally create excessive internal pressure within your creation so as to maximise the wide range of electrical resistance that the velostat offers!
A Look at the Final Product
After much more work was carried out by our company construction man, Intern Jackie, and CEO Akmal, below is our beautiful milestone build (not connected to the TV)! The hardware above was jacked up onto a wooden pallet, and mostly hidden from view underneath the black outer layer of cloth.
My Evaluation
Well, if you ask me, I will say that the velostat was critical in implementing the varying Step States feature that’s used in the Arcade Step Machine above. Despite the challenges I faced implementing the velostat with the soldering of the stripped wire, I found that it was fairly easy to remedy. In fact, had I been more careful and cognizant of the velostat’s sensitivity, this wouldn’t have been a problem in the first place.
A great feature of the velostat that I really did not fully utilise, though, was the wide range of electrical resistance that it offers. Should you want to create a product that has multiple pressure states and you need multiple current threshold values, the velostat really can be of great help. Additionally, my online research has also revealed that the velostat is the actual go-to for DIY enthusiasts to create a DDR Step Machine for its availability, inexpensiveness, flexibility and versatility (it can be folded up, fit into small spaces, curled up, etc.) This means that if you are not looking to create chunky-looking machines, the velostat can be a great component if used creatively.
That said, there are fairly better alternatives out there if the accuracy of electrical current readings is of great import to you. Take a look at Force Sensitive Resistors (FSR). Yes, it is chunky and non-versatile, but it is also tiny and flat, and can be used to fit into small tight crevices in your soon-to-be device. Another advantage that FSRs have over the velostat is that they are more sensitive to pressure, which actually means more accurate readings (and more precaution is needed).
Another similar alternative would also be the Eeontex Conductive Fabric. It looks similar to the velostat, but it’s made of conductive microfiber instead of the plastic (polyethylene) that is the velostat. This makes it a better alternative for wearables and e-textiles, maybe your custom-made electronic watch!
For its simplicity and functionality, though, I find the velostat priced at SGD$9 worth it at its price point. In comparison to other prices found in the market, $9 seems to be right in middle price point. Unless you are tightly bound by budget and need to squeeze every bit of penny you can find, the Velostat will work well for you!
In short, if you’re a DIY enthusiast seeking to build a DIY variable resistor, the velostat is the fairly great and inexpensive purchase for you.
Remarks
Whilst ours doesn’t have the optimal “stepping experience” of a slight depression of a step, other designs found online take on this UX challenge very well! Here’s a cool design that implements the velostat AND the UX challenge I stated above.
Written by Amirul Raziq, currently an intern at Tinkertanker.