@conference {, title = {Ultrasonic Signal Acquisition Module for Smartphone Indoor Positioning.}, booktitle = {Emerging Technologies and Factory Automation, ETFA{\textquoteright}14 }, year = {2014}, month = {09/2014}, pages = {1-4}, publisher = {IEEE}, organization = {IEEE}, address = {Barcelona, Espa{\~n}a}, isbn = {978-1-4799-4845-1/14}, author = {A. Lindo and Mar{\'\i}a del Carmen P{\'e}rez and Ure{\~n}a, J. and Gualda, D and E. Garcia and Jos{\'e} Manuel Villadangos} }