RPI GPIO buffer schematic:|
Page last updated: 07/08/2014 |
RPI GPIO buffer
Design
Provide buffering / level conversion for Raspberry Pi GPIO pins.
Simple design using readily available components.
Low power consumption.
A small and compact design.
Circuit description
A simple and easily constructed using readily available components GPIO buffer for the Raspberry Pi, providing both isolation and buffering for four inputs and four outputs.INPUTS: the four inputs, which are active low in the form of either external closing contacts, transistor, etc to ground. The input pin is held high in the inactive state by a 1k2 resistor to the +12v supply rail, closing one section of a CMOS 4016 bilateral switch, thus grounding the associated RPI GPIO pin. In the active low state, the CMOS 4016 bilateral switch opens allowing the RPI's GPIO pin to be pulled high by a 330R resistor to the +3.3v supply rail. Nb the closed contact or transistor will pass ~10mA
OUTPUTS: each of the four outputs have two changeover relay contacts and one open collector transistor capable of sinking a maximum current of 100mA and maximun open circuit voltage of 50v. The GPIO output pin drives two sections of a ULN2803 Darlington transistor array, one section providing the open collector output whilst the other section is used to control a double pole changeover relay.
INDICATIORS: Nine LED's provide the current status of the RPI GPIO buffer. LED1 +12v power on, LED's 2 through 5 the inputs, and LED's 6 through 9 the outputs.
RPI GPIO buffer component placement / layout:
RPI GPIO buffer PCB bottom trace:
Original Files:
Further to the details of the pages above - the original CAD files created using EAGLE PCB Design software are included below, along with associated PDF files of both schematics and PCB layouts suitable for printing directly.
To use the original CAD files, they must be opened with EAGLE. Visit the CADsoft web site for more details, the software (including a freeware version), part libraries, tutorials, for EAGLE are available.
RPI GPIO PCB component layout PDF