I like digital drawing, and it would be cool if I can draw on the go. I want to develop a smart stylus that has all the standard features and a selling price that undercut everyone by at least 50%. (66% less compare to an Apple Pencil)
The de facto standard of a smart pen is to have the following functions (if not all) :
1. pressure sensing
2. palm rejection
3. shortcut button
So my smart pen must have all of the above and remain affordable. The earphone solution took away the all expensive electronics, controlling circuit, Bluetooth, rechargeable battery and replaced them with a circuit that communicates with an iPad through the standard audio channel. To detect the pressure, the iPad sends a standard wave form to the circuit, the wave form pass through a variable resistor which changes according to the pressure applied on it. The modulated wave form is then sent back to the iPad for comparison.
Other than cost, the earphone circuit is better in terms of:
- Almost all the iOS devices have the connector (the lightning to 3.5mm converter should works)
- Protocol (driver) will be simple, almost like how a modem works.
- Best of all, it is powered by the iPad itself, so no charging ever.
When I knew Apple is going to add a stylus for the iPad, I was pretty happy that It confirmed the need of a stylus for the iPad. However, selling it at US$99 and limited the compatibility to iPad Pro only, make the cost of owner ship to be too high for regular people.