After I had designed a basic rigid stylus with a hole cut out, I then went on to deal with a couple of problems. The first one was that the contact between the glass and the metal didn't feel smooth and I was concerned about the possibility of scratching. The contact O needed a smooth surface, soft enough not to scratch the glass (which, by the way, on an iPad or an iPhone is harder than most metals) and tough enough to last. I tried everything from packing tape, to masking tape, to thin leather, felt and flocking. It had to be soft and slippery, and also thin enough not to interfere with the capacitive touch system.
It took several months but in the end I settled on vinyl film, the kind they use on car and bus advertising. It's soft and flexible and extremely durable (outdoor warranties are for 4 years of rain, snow and sun), and it's also self-adhesive.
Using some artists as testers for these prototypes, I soon discovered the second problem. Yes, the O allowed you to see what you were drawing, but each artist had a particular angle they held the stylus at, and if the O didn't lie flat against the glass, it wouldn't register as a touch. I had settled on 45 degrees as a good compromise angle. But what if you normally drew using a pencil at a 60 degree angle, or signed your name holding a pen at 35 degrees? I had to make the connection between the O and the handle that was flexible or hinged in some way.
Early hinged prototype, April 2010
The first prototype solution used a three-tube hinge soldered on top of a metal O. It seemed logical to put the hinge on the edge so you still had a clear line of sight through the O. This solution worked if the washer contact was heavy enough to flop against the touchscreen with gravity, but it was frustrating because the pushing action to make the contact was off-centre.
This problem led to a contact O with two tubes soldered to the top, in the middle of the O. The pin for the hinge was split so that you had both a clear line of site through the O, and when you pushed down on the O to make contact it naturally lay flat against the screen. The pin wire could become the connection between the handle and the O. The contact pad could also be a thinner lighter weight. This designed allowed the natural hand position I was looking for.
Next early prototype with a two-wire hinge, temporarily attached, April 2010
Now I was really beginning to get somewhere: I had a conductive stylus with a hinged contact pad that allowed you to see through a hole in the middle for more precision than a foam-tip stylus. And the pad had a safe contact surface which glided smoothly on the glass. But there was still a long way to go. More in the next blog post.
Legal note: I am pleased to be able to share this information, but it is my intellectual property. The name oStylus is a trademark, and the ideas in this invention are Patent Pending.