Time-to-Digital converter plug-on module (shield) for Raspberry Pi B+. The board utilizes a TDC7200 (TI) with a time resolution of ~50ps. The Start/Stop inputs to the TDC can be configured with JP2 from either external signals or coming from the RPi's GPIO5 pin in case a timing signal is present at this pin from another plug-on board on the same RPi. Start and Stop signals can be configured from different signals (coming from the input connectors) or the same source (setting "common" on JP3) either supplied from the Start input connector or GPIO5. Read-out of the TDC chip is done through the RPi's SPI bus.