If you need help connecting the SIM900 to the arduino you can check out this tutorial: Guide to SIM900 GSM GPRS Shield with Arduino Here's the connection diagram anyway. From my experience, the second ...

Note that an active-low (L) at pin 1 of connector J2 triggers the security system. Further, an optional “call – alert” facility is added to the security system, which will initiate a telephone call ...

A new switch design method by applying depletion-mode field effect transistor for dual-band GSM switch diplexer module is presented here. If compared with switch module implemented by using PIN diode, ...