RPi Tutorial Easy GPIO Hardware & Software

Warnings
While most of these circuits may interface directly to the RPi, the use of a buffered interface (such as the one supplied by the Gertboard) is recommended which will help protect against damage. Alternatively, experiment with one of the.

The GPIO pins connect directly into the core of the ARM processer, and are static-sensitive, so you should avoid touching the pins wherever possible. If you are carrying a static charge, for example by taking off an acrylic pullover, or walking across a nylon carpet, touching the GPIO pins could destroy your R-Pi, so always earth yourself before touching the pins or anything connected to them.

'''Extreme caution should be exercised when interfacing hardware at a low level, you may damage your RPi, your equipment and potentially yourself and others. Doing so is at your own risk!'''

Aims
This tutorial is based on this thread and aims to introduce basic circuits which can be used with the RPi's General Purpose Input/Output (GPIO). Basic electronics knowledge will be required (i.e. familiarity with typical discrete components such as transistors, diodes and resistors).

It is highly recommended that additional GPIO Protection Circuits are used to protect the delicate GPIO pins if interfacing to RPi hardware.

Useful Links/Resources

 * Tutorial: How to use your RPi like an Arduino - Thorough guide to utilizing the GPIO pins in Python, Bash and C.


 * Online Circuit Lab - Circuit Design and Simulation - Excellent tool for experimenting with circuits (also used for the circuit diagrams used here)


 * Introduction To Embedded Programming - GPIO - In particular there is lots of detailed information about GPIO inputs and outputs for beginners to understand the principles behind the circuits.


 * Microchip's PIC Tips and Tricks PDF - Contains lots of useful example circuits for use with PIC micro-controllers, can be adapted for use with the RPi (3.3V GPIO).


 * The Electronics Club - An excellent resource for beginner electronics, explains many basic circuits.

Protection Circuits
In order to protect the Raspberry Pi hardware, it is highly recommended that the GPIO pins are protected in some form to avoid damage.

The following link will introduce some of the ways to do this:

GPIO Protection Circuits

Alternative Test Platforms
Until you have a RPi to test with, there are many alternative platforms available which will allow the testing of basic circuits. In addition, they may be interfaced with directly using the RPi in the future.


 * TI LaunchPad - A low cost development platform ($4.30 including free world shipping). Includes programmer/debug board, two processors (with 16 GPIO including I2C/SPI/UART, 8ch 10bit ADC etc).


 * Arduino - Common hobbyist development platform. Excellent community support and additional hardware.


 * PICAXE


 * STM32 Primer/EvoPrimer - Self-contained development platform. Mentioned since I may use one at some point (I bought the original Primer a long time ago). It includes a battery, acceleration sensors and built in display screen.

=Completed Tutorials= Note: Until RPi devices are available, I can not confirm this will work on a real RPi. For now, I shall be using the TI LaunchPad (see Alternative Test Platforms for details) to test the hardware on (as it is cheap and the logic levels similar).

Basic Circuits
1. LED output

Directly driven (will need very low powered LED) or driven via transistor (allowing higher current). Includes example 8xLED Test Module.

3. Simple on/off switch input

With or without de-bouncing, protection resistors etc. Includes example 8xSwitch Test Module.

4. 12V relay driver circuit

12V relay driver circiut with opto-decoupler. Includes schema.

=Planned Tutorials=

Basic Circuits
1. LED output

Completed see above.

2. Small DC motor drive

MOSFET or Darlington Pair to provide high power drive and reverse bias diode to protect from motor coils.

3. Simple on/off switch input

Completed see above.

4. Analogue resistive sensor sampled as a digital input

Using a basic transistor switch circuit.

Intermediate Circuits
1. Shift Registers - Multiplexing Data

An introduction to using additional ICs. In this case, using a parallel to serial 8-bit shift register to read 8 digital inputs using two GPIO pins.

2. Analogue to Digital Circuit

Use of a ADC chip to sample inputs.

3. PWM Driving Circuit

For example motor speed control.

4. Alpha-numeric 2x16 LCD Display

(IN-PROGRESS) Control via 4-wire data (total 6 GPIO) and also alternative 2-wire interface circuit.

5. Interfacing to I2C Devices

Interfacing to an I2C device connected to one of the Pi's I2C buses.

Advanced Circuits
1. Control Hardware Over The Internet

Implement web control and monitoring of GPIO connected components.

2. Communicating With Other Micro-controllers

Communicate with other micro-controllers so that features such as ADCs can be used.

Contributing to this tutorial
This is an open project so please feel welcome to add your own sections and improve its content.

Please see the Talk:RPi Tutorial Easy GPIO Hardware & Software page to discuss this page.