US 8149227

Removing click and friction noise in a writing device

Systems for removing or attenuating friction and/or click noise generated during writing with a smart pen are disclosed. In a smart pen, the writing cartridge is biased towards a first side of the smart pen internal cavity by a low-force biasing system without affecting writing cartridge movement. For example, the writing cartridge is comprised of a magnetic material and a magnet is embedded into the first side of the smart pen internal cavity to bias the writing cartridge towards the first side. Alternatively, the material comprising the writing cartridge or smart pen internal cavity is modified, reducing friction between the components. As another alternative, a DSP method identifies analyzes one or more parameters of received audio data to differentiate click noise from audio data, and may receive data from a movement sensor indicating when the writing cartridge has moved to reduce power consumption for identifying click noise.