USB-UART converter with FT230XS and external 3.3V power supply
You can buy a lot of USB-UART converters e.g. with FT232, CH340 or CP2102. Each of USB-UART converters has some advantages or disadvantages. Some doesn't have drivers inside kernel (linux) and/or windows. Another has a problem with faster communications. I wanted to design own USB-UART converter and so I chose another IC for convert between USB and UART. Broads is designed for beginners as one-sided PCB with a few jumpers. I like IC by FTDI chip company. FT230XS.

SIM908 - AT commands
If you have our development board with SIM908 or something else, you have to know AT commands for GSM/GPRS/GPS module. Repetition again. You have to connect UART from SIM908 module to your microcontroller (Tx module - Rx microcontroller, Rx - module - Tx microcontroller). You can use USB-UART convertor. A lot of AT commands is same for SIM900 and another SIM types.

SIM908 - development board
I had to create development board with SIM908 - GPS&GSM&GPRS module for diploma thesis. The board is designed as top side. It's easier than top and bottom sides. On the board are pin headers which are connected to the SIM908 (some out/in). Notes for develompent board.

Switching power supply - Step down converter LM2576
I needed power supply (step down converter) for my big project with minimal 2A current and fixed output voltage (3.3V) or adjustable output voltage. I wanted higher efficiency and that's why I chose switching power supply with LM2576 circuit. I designed the circuit so I could replace LM2576 with fixed output voltage (3.3V, 5V, 12V etc.) for LM2576 with adjustable output voltage. If you want to use fixed output voltage, replace the resistor R2 for 0R value and resistor R1 will not be involved. If you want tu use adjustable version (1.23 - 37V), you calculate values of resistor in the datasheet. The efficiency of 3.3V version is 75%, 5V 77%, 12V 88% and adjustable version is 77%.

Step-down MC34063 - 12-3.3V/500mA
This is next circuit switching converter. This converter reduces the voltage from 12V to 3.3V with very popular DC/DC converter MC34063. A efficiency is 73.086%. The switching converter was designed for 500mA with max ripple 100mV. When measuring ripple was the current drawn 550mA. Frequency of switching was 68KHz...