I believe that you’ve got the raspberry pi 3/2B you want. At now you need to prepare a expansion board for your pi. DVK512 is a good choice, it integrates various components and interfaces for connecting external accessory boards. It's ideal for Raspberry Pi evaluation and development. Here is functional structure chart:
1, Pinheaders for connecting with the RPi
2, UART interface: easily connects to UART modules such as RS232, RS485, USB TO UART, etc.
3, 8I/Os interface: easily connects to modules controlled by I/Os, such as 8 Push Buttons, Logic Level Converter, Mix Board, etc.
4, SPI interface: easily connects to SPI modules such as AT45DBXX Dataflash, L3G4200D Board, etc.
5, I2C interface: easily connects to I2C modules such as PCF8574 Expansion Board, PCF8563 RTC Board, LSM303DLHC Board, etc.
6, Character LCD interface: for connecting character LCDs like LCD1602
7, USB connector: USB TO UART, supported by onboard converter CP2102
8, Power indicator
9, User LEDs
10, User Keys
11, Potentiometer: for LCD1602 contrast adjustment
12, RTC battery holder
13, PCF8563: onboard RTC chip
14, 32.768K crystal: RTC crystal
15, CP2102: onboard USB TO UART chip, for debugging
16, CP2102 jumper
17, RTC jumper
18, User LEDs jumper
19, User Keys jumper