When interfacing between two devices such as a Raspberry Pi with 3V3 I/O and a PICMicro running at 5V voltage level conversion is necessary. A simple method to do this on a breadboard is to use a pre-built adapter.

Two of the more popular types found at places like eBay are two channel bi-directional I2C level converters and four channel general purpose converters.

These devices contain two mosfets with pull-ups resistors in the arrangement specified by the Philips I2C interfacing application note (link below).

They also have an additional component which is a 3V3 LDO voltage regulator. This addition is to allow a 5V device to directly interface with a 3V3 device and also power it.

Although marketed for I2C they can be used for anything that demands two channels of bi-directional voltage level conversion.

3V3 OUTPUT  BVCC    AVCC  5V INPUT
3V3 CLOCK   BSCL    ASCL  5V CLOCK
3V3 DATA    BSDA    ASDA  5V DATA
GROUND      BGND    AGND  GROUND

There is a speed impact when using these device which have a slow rise time. For example, when using ICSP with Pickle Microchip PIC ICSP it was found that raising the SLEEP configuration value to 8 was necessary.

Level shifting techniques in I2C-bus design