One of the biggest strengths of the Arduino ecosystem is the concept of Shields: add-on boards which piggyback on top of the Arduino itself to add functionality, ranging from network connectivity and additional sensors to H-bridges for driving motors. Sometimes, though, you don't have a particular Shield to hand for a given experiment, and you don't want to invest cash before you're sure the project has wings. The solution: VirtualShield.
The creation of Jakarta-based developer Saggaf Arsyad, the open-source VirtualShield turns any Android device with Bluetooth support into a series of software-driven shields. Using nothing more than a normal Arduino board or compatible and a low-cost Bluetooth transceiver module, the VirtualShield provides - at present - three independent Shield capabilities: the Internet Shield, which uses the internet connection on the Android device to send or receive data via HTTP; the Location Shield, which uses the GPS receiver - if present - to retrieve the user's current location; and the Accelerometer Shield, which provides a live feed of the Android device's movement in 3D space.
The Android portion of the VirtualShield software runs in the background on the device, meaning it can be always accessible, and the use of Bluetooth rather than a wired connection means your prototype isn't at risk of being demolished as you move around. Saggaf has indicated that he's working on adding support for more Shield types, and there's certainly plenty to choose from: a modern Android smartphone has a wealth of sensors on board, from magnetometers to proximity sensors, not to mention at least one on-board camera.
If you fancy giving VirtualShield a go yourself, Saggaf has written a getting started guide, and is actively seeking feedback from users so the project can be improved.
VirtualShield is a prototyping toolkit for Arduino. The toolkit uses your Android device to act like Arduino Shield and sensors, such as sending data to Middleware or getting location data. The toolkit can help you learn Arduino with less cost and less code. Now, let's get build things!