Rev 1

This revision had 2 major improvements: The ability to hot swap a 5V barrel jack connector with the battery so that the battery can be removed for charging, and the use of a SIM900 card. We’re currently awaiting the shipment of this board.

The SIM900 chip has the same command set as the SIM5100B but it is faster and could be soldered directly onto a PCB with the rest of the power circuitry.  The SIM5100B chip that we had purchased before was made specifically for the breakout board that we used with it, so we couldn’t just solder it directly without another adapter.  We decided against spending more money since we didn’t need to purchase the SIM900 chip as a fellow TIer let us use one of his that he had previously purchased was not using.  Another benefit of using the SIM900 is that we saved some space by placing everything on one PCB.

SCH_sim

Sim 900 Connectivity(does not change with revisions)

A video explaining the schematic basics with the components and connections that do not change with revisions can be found under Design->Demo Videos

One of the major issues with Rev 0 was that the battery needed to be removed before hooking up to a wall supply.  This meant that if the battery was low on power, the phone must be shut off, the battery removed, and the phone plugged in and rebooted in order to prevent overpowering the board.  We fixed this problem by purchasing a separate barrel connector that acted as a switch (RAPC722X).  We then wired the battery through this connector on the power board.  When a barrel jack was connected, the power from the battery would be automatically disconnected from the circuit and replaced with the 5V power, allowing for a seamless transition before removing the battery.

A video explaining the schematic for Rev1 can be found in the under Design->Demo Videos

Special Thanks to TIer Bob Harbour 

SCH_led

LED Driver

SCH_rev1

Power Circuitry

PCB_rev1

PCB Layout

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