In my summer internship, we got a task to make an interactive wall decoration for our lab. Being amazed by the cool artistic project videos, we decided to use Bare Conductive. The idea of using versatile painting to create touchable triggers raises our interests. It gives designers great space for pervasive interaction design.
According to the examples posted on Bare Conductive Blog, the most popular use cases are sound, light switch and shape projections. For our first trial, we decided to explore sound interaction on a whole whiteboard wall as well a relatively small space on a window.
We have a Touch Board Pro Kit and some extra 50ml Electric Paint jars. It only took a few minutes to trigger the touch, but very much longer to make a workable wall paint. We failed and gained in the two-week experiments. We tried different approaches with copper tape, paint and iron wires, to make the lines conductive and stable. I feel encouraged to write this blog. Hopefully, it can shorten some others’ experimental time.
How Electrodes Respond to Touches
There are 12 capacitive sensors on the Touch Board. The capacitive sensors detect permittivity changes. Once the circulate is on, the board would measure the circulate capacitance, set it to an initial value. When a human hand touches or approaches, the capacitance would change. If the change exceeds a pre-defined threshold, the board would trigger an event programmed in Arduino.
One way to visualize the triggering process is to use Datastream code and Grapher in Processing. DataStream code can be upload through Arduino to the board. Although the retrieved data is a bit unreadable, MPR121 Grapher in Processing can help in visualizing.
In the visualization,
- Yellow and green lines are presenting touch and release thresholds.
- The red line starts at the blue line, goes along primitivity changes.
- A touch is expected to make the red line goes down below the touch threshold, then there will be a pink vertical line showing an event triggered.
- When the touch ends, the red line goes up back to the blue line, and a vertical white line shows “released”.
- The blue line is the baseline. It is set based on the primitivity value at the moment the circulate is turned on, which is supposed to be in the top above the yellow and green lines.
On the Touch Board, there is a signal light for quick reference. The light is off by default. When a touch is detected, the light is on. In some of my failed experiments, the light is always on even when the board is left alone. It took me a while to debug the failure. I checked the Grapher, found the red line never goes back to the blue line — the initial state. I made sure nothing is nearby interrupting the circulate, but the light is still on. After some trials, it turns out to be the initial state is set to an erring value in the very beginning, due to unwanted capacitance interruption. The initial value is set based on the capacitance at the moment the circulate is on. I should be very careful with the surrounding conductive materials when I flip the switch.
Tips for debugging:
- At the moment it is switched on, the circulate should not contact any other conductive object that is not part of the circulate.
- The board itself is conductive, so holding the board would impact the initial capacitance status.
Even though the initial status is set correctly, the circulate may still not work as expected… It is usually because the circulate is break or the conductivity fails at some point. An ammeter is helpful in checking the connectivity on any part of a circulate.
In our project, we first used conductive paint largely, as it is aesthetic and flexible in drawing patterns. However, the electric connectivity breaks frequently. I tried to find out why the to circulate is not as responsive as we expected.
- Firstly, we read from Bare Conductive tutorial: the wider the line is drawn, the larger the resistance is. So we replaced the wide lines with a thinner design. The change actually made our connected circulate go further, but still not solving the problem.
- Secondly, we read more from Bare Conductive blogs, found diluting the paint can make it smoother and more conductive. So we followed the advice, using Flow-Aid to thin the paint. It made painting much easier and it is helpful in improving conductivity. Still, the circulate isn’t robust in responding touches.
- Lastly, we started blaming the wall paint material. Since the wall is intended to be used as a whiteboard, the surface may be too lumpy. We feel it may influence the connectivity. To prove our guess(blame), we painted a long tape on top of the wall. And it works!
We also experimented with copper tape. We made a copper tape collage to visualize sound. Here are two take-ways for using copper tape:
- The sticky side of the copper tape is not very conductive. It might not be a good idea to stick the copper tape on top of another… They will not be connected well. This can be checked by an ammeter.
- On Bare Conductive website, the copper tape sticks to the board electrode nicely… However, we found in our experiment twinning the tape around the electrode is less pretty but more robust than sticking.
Yes. Iron Wire is the most conductive material we’ve ever had. But it is usually too sensitive to use, as it is usually naked without a place to hold with bare hands.
Get started with your touch board: [Getting Started with the Touch Board — Bare Conductive](https://www.bareconductive.com/make/introducing-the-touch-board/)
What is capacitive sensing: [What is capacitive sensing — Bare Conductive](https://www.bareconductive.com/make/what-is-capacitive-sensing/)
Connect to Arduino:[Setting up your Touch Board with the Arduino Installer — Bare Conductive](https://www.bareconductive.com/make/setting-up-arduino-with-your-touch-board/)
Visualization: [Touch Board + Grapher — Bare Conductive](https://www.bareconductive.com/make/touch-board-grapher/)
Resistance test [How to use a multimeter with Electric Paint — Bare Conductive](https://www.bareconductive.com/make/use-a-multimeter-with-electric-paint/)
[How to thin Electric Paint — Bare Conductive](https://www.bareconductive.com/make/how-to-thin-electric-paint/)