This is a basic GPIO board for the raspberry pi that brings out 12 GPIO lines(At 3.3V I/O) the I2C and

power ports via a set of input and output buffers to terminal blocks to allow for easier wiring to external circuits. It also consists of 12 LED’s that indicate the state of the logic signal.

Schematic 1:- Input buffers, Power, Input selection and terminal blocks

Schematic 2 :- Output buffers and  LDO

The 12 input/output connector terminal blocks are connected to GPIO A-K and output selection is chosen with jumpers between J6 & J8. Input selection is chosen by placing jumpers between J3 & J4, Try to ensure that each of the GPIO terminal A-K is selected as either an input or an output.

All terminal connections connect back through U2 A&B and U3B to the LED indicators that indicate the

logic levels at terminal blocks.If connected as an input then this signal is also routed back to Raspberry pi GPIO connector via a 10K resistor. This ensures that if connected to an output by mistake then there is

no shorted connection.

The PCB is a 2 layer board designed for through hole components, power present is indicated by D13.

The bill of materials for this project is

Bill Of Materials

=================

 

QTY  PART-REFS           VALUE              

---  ---------           -----              

Resistors

---------

12   R1-R12              1k                 

13   R13-R25             10k                

 

Capacitors

----------

3    C1-C3               100nF              

2    C4,C5               10u                

 

Integrated Circuits

-------------------

3    U1-U3               SN74AHC244N        

1    U4                  MCP1702            

 

Diodes

------

13   D1-D13              LED                

 

Miscellaneous

-------------

1    CN1                 CONN-DIL26         

1    J1                  TBLOCK-I8          

1    J2                  TBLOCK-I4          

4    J3,J4,J6,J8         CONN-H12           

2    J5,J7               TBLOCK-I3  

Connecting up to WiringPi

In order to test the board I’m using the excellent WiringPi from Gordons Projects go to his website and follow the download instructions for installing WiringPi. The table below shows how wiringPi Maps to the GPIO

Board.

Writing a small script below or download here

#!/bin/bash

for i in 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16; do gpio mode $i out; done

while true

do

for i in 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16; do gpio write $i 0; done

sleep 1;

gpio write 5 1

sleep 1;

gpio write 4 1

sleep 1;

gpio write 3 1

sleep 1;

gpio write 2 1

sleep 1;

gpio write 1 1

sleep 1;

gpio write 0 1

sleep 1;

gpio write 14 1

sleep 1;

gpio write 12 1

sleep 1;

gpio write 13 1

sleep 1;

gpio write 10 1

sleep 1;

gpio write 11 1

sleep 1;

gpio write 7 1

sleep 1;

done

Lets the GPIO board switch on each output in turn as in the video below

Controlling from Python

Now the board is functional we can try and control it from python, this is my first python program so be

kind.. so this is a small LED chaser program it switches each LED on in order for 1 second and then

moves onto the next one when it reaches the end it does the reverse and continues in an infinite loop. 

First I installed Geany as an Editor type

apt-get install geany

Next make sure it builds using sudo as explained here

Run geany from the start menu under programming languages and either download LED Chase.py

or type in the code below not elegant I know but it does the job.

#!/usr/bin/env python

import RPi.GPIO as GPIO

from time import time, sleep

GPIO.cleanup()

GPIO.setwarnings(False)

GPIO.setmode(GPIO.BOARD)

GPIO.setup(18, GPIO.OUT)

GPIO.setup(16, GPIO.OUT)

GPIO.setup(15, GPIO.OUT)

GPIO.setup(13, GPIO.OUT)

GPIO.setup(12, GPIO.OUT)

GPIO.setup(11, GPIO.OUT)

GPIO.setup(23, GPIO.OUT)

GPIO.setup(19, GPIO.OUT)

GPIO.setup(21, GPIO.OUT)

GPIO.setup(24, GPIO.OUT)

GPIO.setup(26, GPIO.OUT)

GPIO.setup(7, GPIO.OUT)

while 1:

GPIO.output(18, True)

sleep(1)

GPIO.output(18, False)

GPIO.output(16, True)

sleep(1)

GPIO.output(16, False)

GPIO.output(15, True)

sleep(1)

GPIO.output(15, False)

GPIO.output(13, True)

sleep(1)

GPIO.output(13, False)

GPIO.output(12, True)

sleep(1)

GPIO.output(12, False)

GPIO.output(11, True)

sleep(1)

GPIO.output(11, False)

GPIO.output(23, True)

sleep(1)

GPIO.output(23, False)

GPIO.output(19, True)

sleep(1)

GPIO.output(19, False)

GPIO.output(21, True)

sleep(1)

GPIO.output(21, False)

GPIO.output(24, True)

sleep(1)

GPIO.output(24, False)

GPIO.output(26, True)

sleep(1)

GPIO.output(26, False)

GPIO.output(7, True)

sleep(1)

GPIO.output(7, False)

GPIO.output(26, True)

sleep(1)

GPIO.output(26, False)

GPIO.output(24, True)

sleep(1)

GPIO.output(24, False)

GPIO.output(21, True)

sleep(1)

GPIO.output(21, False)

GPIO.output(19, True)

sleep(1)

GPIO.output(19, False)

GPIO.output(23, True)

sleep(1)

GPIO.output(23, False)

GPIO.output(11, True)

sleep(1)

GPIO.output(11, False)

GPIO.output(12, True)

sleep(1)

GPIO.output(12, False)

GPIO.output(13, True)

sleep(1)

GPIO.output(13, False)

GPIO.output(15, True)

sleep(1)

GPIO.output(15, False)

GPIO.output(16, True)

sleep(1)

GPIO.output(16, False)

GPIO.output(18, True)

sleep(1)

GPIO.output(18, False)

Controlling the GPIO Port from a GUI

Taking this one step further and combining Tkinter and GPIO lets

us control the outputs from a GUI. You can click on the buttons to toggle

the GPIO outputs on or off represented by a 0 or a 1. The python code

can be downloaded here.