All 26 GPIOs are buffered with bi-directional voltage translators to protect the RPi when experimenting with new circuits. Two different PCBs, a normal and a T-board version.
Both PCBs have two resettable fuses (F1, F2) to protect the +5 V and +3.3 V power supply of the RPi. Additionally for I2C extra pull-up resistors R1 and R2 can be enable by jumpers JP1 and JP2. The B-port I/O’s of the ICs (these are the buffered ports of the PCB’s) can be set to +3.3 V or +5 V logic by jumper JP3.
Connecting the RPi side of the PCBs can be done by a short 40way ribbon cable with two 2x20 receptacle connectors if K1 is an ordinary 2x20 pin header.
The board-to-board connector from Harwin with 32 contacts we used in our T-board prototype to connect the PCB to a breadboard has to be split in two 16 connectors (K2,K3). Each contact has a thicker and thinner pin. The thicker part of the contacts should be soldered to the PCB.