RPI: Use GPIO pins and a program to determine TTL gates

Lab Outline

  • Download WiringPi libraries
  • Understand the pin layout for the RPI
  • Understand why you must use a voltage converter in this lab, and how to use it
  • Create a program to determine the type of TTL gate being tested

Use GPIO pins and a program to determine TTL gates

DUE BY NEXT LAB

Wiring Pi Libraries

If you have not downloaded the WiringPi libraries, you must do so as you cannot write a program to work with the GPIO pins otherwise. Instructions are below:

If you have Internet connection follow these steps.

Connect to your Pi and, in the terminal, type:

sudo aptitude install git-core

Allow the installation of git, and once it is installed, type:

git clone git://git.drogon.net/wiringPi
cd wiringPi
./build

If you do not have Internet connection, ask your PSO instructor for a flash drive containg the wiringPi libraries and connect it to you Pi. Or you can just as easily go to the url: https://git.drogon.net/?p=wiringPi;a=summary and select the “snapshot” of the top most version. Unizip the download, put it on a USB stick. Then type the following:

sudo mkdir /mnt/usb
sudo mount /dev/sda1 /mnt/usb
cp -r /mnt/usb/wiringPi .
cd wiringPi
./build

The build script included in the wiringPi package will automatically install wiringPi for you.

You can make sure the installation worked correctly by typing:

gpio -v
gpio readall

GPIO Pin layout for RPI

Important: The most essential thing you must remember first before anything is that your RPI cannot handle voltage above 3.3 volts. You have previously been using 5 volts on your breadboard. Thus the necessity for a voltage converter which will be discussed in the next section. Simply stated, your RPI will output 3.3 volts on any GPIO output pin, your TTL gates require 5 volts(thus a conversion is needed) and then going back into your RPI will require the 5 volts to be converted back to 3.3 volts.

Use GPIO pins and a program to determine TTL gates

The information below explains how the GPIO pins work and how there numbering works, you have to read it a few times to get it:

Dealing with the pins on the Pi can be somewhat tricky, as there are three different pin numbering systems to keep track of on the Pi. They are:

  • The Pi’s internal pin numbering,
  • The GPIO pin labels, and
  • wiringPi’s internal pin numbering.

In short, when programming using wiringPi, use the wiringPi pin number associated with a particular Raspberry Pi pin to control it – i.e. setting pin 0 to high in wiringPi sends 3.3V to pin 11 on the Pi.

Provided below is a table3) that contains all of the relevant pin numbers for each pin.

wiringPi pin GPIO pin Name Pi pin (bot row) Pi pin (top row) Name GPIO pin wiringPi pin
3.3V 1 2 5V
8 2 SDA0 3 4 5V
9 3 SCL0 5 6 Gnd
7 4 GPIO 7 7 8 TxD 14 15
Gnd 9 10 RxD 15 16
0 17 GPIO 0 11 12 GPIO 1 18 1
2 27 GPIO 2 13 14 Gnd
3 22 GPIO 3 15 16 GPIO 4 23 4
3.3V 17 18 GPIO 5 24 5
12 10 MOSI 19 20 Gnd
13 9 MISO 21 22 GPIO 6 25 6
14 11 SCLK 23 24 CE0 8 10
Gnd 25 26 CE1 7 11

 

Source: RPI: Use GPIO pins and a program to determine TTL gates

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