Abstract: A digital pen comprising a skeleton and a removable skin: the skeleton holding together in fixed relationship: an electric circuit; an acoustic transmitter, detached from said electric circuit, and configured to transmit acoustic signals; and a resilient holder, configured to mechanically press said electric circuit into electrical contact with said transmitter, so as to electrically connect said electric circuit and said transmitter; and the removable skin comprising a housing fitting over said skeleton.

Abstract: A digital pen comprising: an electric circuit, an acoustic transmitter, detached from the electric circuit, and configured to transmit acoustic signals, and a resilient holder, configured to mechanically press the electric circuit into electrical contact with the transmitter, so as to electrically connect the electric circuit and the transmitter.

Abstract: A MEMS microphone comprising: a) a case with an open front side; b) a MEMS membrane mounted on one face of a base, the base being mounted inside the case on a substantially closed side; and c) a mesh covering the front side, substantially transparent acoustically to at least some of a range of operating frequencies at which the microphone is sensitive.

Abstract: A digital pen comprising: an electric circuit, an acoustic transmitter, detached from the electric circuit, and configured to transmit acoustic signals, and a resilient holder, configured to mechanically press the electric circuit into electrical contact with the transmitter, so as to electrically connect the electric circuit and the transmitter.

Abstract: A digital pen comprising: an electric circuit, an acoustic transmitter, detached from the electric circuit, and configured to transmit acoustic signals, and a resilient holder, configured to mechanically press the electric circuit into electrical contact with the transmitter, so as to electrically connect the electric circuit and the transmitter.

Abstract: A receiving unit for receiving an acoustic signal from a digital pen, comprises: at least two ultrasound receivers, for receiving ultrasound signals from the digital pen; an electric circuit connected to said ultrasound receivers, and configured to extract ultrasound signals received by said ultrasound receivers, to enable tracking a position of said pen, and a biased clip for holding paper in fixed relationship to said ultrasound receivers. The clip may be metal, and alignment and location features may be provided for fitting sheets of paper for writing.

Abstract: A receiving unit for receiving an acoustic signal from a digital pen, comprises: a housing; at least two ultrasound receivers, for receiving ultrasound signals from the digital pen, the ultrasound receivers comprising electret microphones, the electret microphones being located in location holes in the housing; and an electric circuit connected to said electret microphones, to extract ultrasound signals received by the ultrasound receivers. An attachment device may removably attach the receiving unit to another item.

Abstract: A digital pen comprising a skeleton and a removable skin: the skeleton holding together in fixed relationship: an electric circuit; an acoustic transmitter, detached from said electric circuit, and configured to transmit acoustic signals; and a resilient holder, configured to mechanically press said electric circuit into electrical contact with said transmitter, so as to electrically connect said electric circuit and said transmitter; and the removable skin comprising a housing fitting over said skeleton.

Abstract: A MEMS microphone comprising: a) a case with an open front side; b) a MEMS membrane mounted on one face of a base, the base being mounted inside the case on a substantially closed side; and c) a mesh covering the front side, substantially transparent acoustically to at least some of a range of operating frequencies at which the microphone is sensitive.

Abstract: A digital pen comprising: an electric circuit, an acoustic transmitter, detached from the electric circuit, and configured to transmit acoustic signals, and a resilient holder, configured to mechanically press the electric circuit into electrical contact with the transmitter, so as to electrically connect the electric circuit and the transmitter.