7 Segment Display with MCP23S17

The temperature shall be displayed by using two 7 segment displays. To save some of the GPIO ports of the Pi the way of choice was a port expander. I decided to use the MCP23S17 which I bought over here. The MCP23S17 is controlled via the SPI bus, which comes in handy, as it is possible to extend the display very easily by adding new 7 segment units and additional MCP23S17s on the same bus. The port expander provides two banks with 8 ports each which is just enough to steer one 7 segment display.

7Segment mit MCP23S17
The picture above shows the layout in the Fritzing software.

7Segment mit MCP23S17
And this one how it actually looks on the breadboard.

The script is called with two parameters, e.g. perl ./7segments.pm 1 2. In this case this would generate the number 12 to be displayed. Every parameter different to a number from 0-9 turns the respective 7 segment display off.

#!/usr/bin/perl

use Device::BCM2835;
use strict;

# call set_debug(1) to do a non-destructive test on non-RPi hardware
# Device::BCM2835::set_debug(1);
Device::BCM2835::init()
|| die "Could not init library";

# Variables
my $test;
my $param1;
my $param2;

# read CLI params
($param1, $param2) = @ARGV;

if ($param1 !~ /[\d]/ || $param1 > 10) {
 $param1 = 10;
}

if ($param2 !~ /[\d]/ || $param2 > 10) {
 $param2 = 10;
}

# MCP23S17 Values
my $SPI_SLAVE_ADDR = 0x40;
my $SPI_IOCTRL     = 0x0A;
my $SPI_IODIRA     = 0x00;
my $SPI_IODIRB     = 0x01;
my $SPI_GPIOA      = 0x12;
my $SPI_GPIOB      = 0x13;

# MCP23S17-PINs
my $SCLK = 11;  # PIN11 = Serial-Clock
my $MOSI = 10;  # PIN10 = Master-Out-Slave-In
my $MISO = 9;   # PIN9  = Master-In-Slave-Out
my $CS   = 24;  # PIN24 = Chip-Select

# Digit Values
my @output10 = ( 0b10000001, 0b11100111, 0b10010010, 
                 0b11000010, 0b11100100, 0b11001000, 
                 0b10001000, 0b11100011, 0b10000000, 
                 0b11000000, 0b11111111 );
my @output1  = ( 0b10000001, 0b11111001, 0b01000101,
                 0b01100001, 0b00111001, 0b00100011,
                 0b00000011, 0b11110001, 0b00000001,
                 0b00100001, 0b11111111 );

# Set RPi pin 11 to be an OUTPUT
Device::BCM2835::gpio_fsel($SCLK, BCM2835_GPIO_FSEL_OUTP);
# Set RPi pin 10 to be an OUTPUT
Device::BCM2835::gpio_fsel($MOSI, BCM2835_GPIO_FSEL_OUTP);
# Set RPi pin 9 to be an INPUT
Device::BCM2835::gpio_fsel($MISO, BCM2835_GPIO_FSEL_INPT);
# Set RPi pin 24 to be an OUTPUT
Device::BCM2835::gpio_fsel($CS, BCM2835_GPIO_FSEL_OUTP);

# prepare the edge
Device::BCM2835::gpio_write($CS, 1);
Device::BCM2835::gpio_write($SCLK, 0);

# subroutine sendValue
sub sendValue {
 # send value
 my $i = 0;
 my $value;
 ($value) = @_;
 while ($i < 8) {
   if ($value & 0x80) {
     Device::BCM2835::gpio_write($MOSI, 1);
   } else {
     Device::BCM2835::gpio_write($MOSI, 0);
   }
   # generate falling edge for the clock signals
   Device::BCM2835::gpio_write($SCLK, 1);
   Device::BCM2835::gpio_write($SCLK, 0);
   $value <<= 1; # shift bit 1 position to the left
   $i ++;
 }
}

# subroutine sendSPI
sub sendSPI {
 # CS active (LOW-Aktiv)
 Device::BCM2835::gpio_write($CS, 0);

 my($opcode, $addr, $data);
 ($opcode, $addr, $data) = @_;

 $test = &sendValue($opcode); # send OP-Code
 $test = &sendValue($addr);   # send address
 $test = &sendValue($data);   # send data

 # CS not active
 Device::BCM2835::gpio_write($CS, 1);
}

# Initialise MCP23S17
$test = &sendSPI($SPI_SLAVE_ADDR, $SPI_IODIRB, 0x00); # GPPIOB as INPUT
$test = &sendSPI($SPI_SLAVE_ADDR, $SPI_GPIOB, 0x00);  # Reset GPIOB
$test = &sendSPI($SPI_SLAVE_ADDR, $SPI_IODIRA, 0x00); # GPPIOA as INPUT
$test = &sendSPI($SPI_SLAVE_ADDR, $SPI_GPIOA, 0x00);  # Reset GPIOA

# Send Data
$test = &sendSPI($SPI_SLAVE_ADDR, $SPI_GPIOB, $output10[$param1]);
$test = &sendSPI($SPI_SLAVE_ADDR, $SPI_GPIOA, $output1[$param2]);

The great tutorial from Erik Bartmann which you can find over here helped me a lot to get this running. You may want to check out his site http://erik-bartmann.de.

IR distance sensor

I want the (still to be added) display only to be powered up when someone is within the range of the device to save some energy. For the implementation of this function I decided to start with an already assembled IR distance sensor from Sharp.

As this sensor is an analog sensor the analog voltage out will range from 3V when an object is only 10 cm away and 0.4V when the object is 80 cm away. Unfortunately the Pi does not have any analog inputs.

My rescue was the great post from Matt @ raspberry-spy.co.uk, where he explains how to measure different light levels on the Raspberry Pi.

So I started from re-building his circuit and run some test measurements, this is how it looked on my breadboard.
LDR with capacitor

For a detailed overview including the Fritzing views please check out Matt’s post. Once I had replicated this set-up successfully I added the IR distance sensor.IR distance sensor on breadboard

With the following code I am able to count how many loops it takes until the capacitor voltage has increased enough to be considered as a HIGH by the GPIO pin (approximately 2V). The number of loops is proportional to the distance of an object in front of the sensor.

#!/usr/bin/perl

use Device::BCM2835;
use strict;

# call set_debug(1) to do a non-destructive test on non-RPi hardware
# Device::BCM2835::set_debug(1);
Device::BCM2835::init()
|| die "Could not init library";

# Variables
my $ir_pin = 24;
my $measurement =0;

# logfile handling
sub logging {

  my $logfile = "/appco.de/log/appco.de.log";

  if ( ! open LOG, ">>", $logfile ) {
    die "Kann Logdatei nicht anlegen: $!";
  }

  my ($sekunden, $minuten, $stunde, $tag, $monat, $jahr) = localtime;
  my $echtes_jahr = $jahr + 1900;
  my $echter_monat = $monat + 1;
  printf LOG "%s.%02s.%02s %02s:%02s:%02s %s\n", $echtes_jahr, $echter_monat, $tag, $stunde, $minuten, $sekunden, $_[0];
  close LOG;

}

while (1){
  # Discharge capacitor
  # Set GPIO pin to OUTPUT
  Device::BCM2835::gpio_fsel($ir_pin, BCM2835_GPIO_FSEL_OUTP);
  # Set GPIO pin to LOW
  Device::BCM2835::gpio_write($ir_pin, LOW);
  sleep (0.1);

  # Set GPIO pin to INPUT
  Device::BCM2835::gpio_fsel($ir_pin, BCM2835_GPIO_FSEL_INPT);

  $measurement = 0;

  # Count loops until voltage across
  # capacitor reads high on GPIO
  while (Device::BCM2835::gpio_lev($ir_pin) == 0){
    $measurement ++;
    sleep (0.2);
    # stop measuring after 100.000 loops
    if ($measurement > 100000){
      &logging ("canceled");
      last;
    }
  }

  &logging ("$measurement");

}

At the moment the sensor is always powered on, which is probably wasting more energy than I am intending to save by the use of the sensor.

For the future the sensor should only be powered up when the PIR sensor detected a movement and I also want to replace the ootb sensor with a much cheaper solution made out of IR LEDs and an IR receiver.

Temperature and humidity sensor

To control the heating, the Pi needs to know temperature and humidity, this is possible by using the combined sensor DHT22. I got my unit from Adafruit here. It comes with the required 4.7K – 10K resistor, to be used as a pullup from the data pin to VCC. How the wiring on the breadboard works you can see depicted further below.

Initially I wanted to interface the DHT22 temperature and humidity sensor with perl. After some time it became obvious that perl on the Pi is not fast enough to read successfully from the sensor.

At that point I decided to use the great C-code from Adafruit (available on Github) and simply embed it into my perl script. A very useful tutorial from Adafruit is available here.

The picture below shows how the wiring looks like on the breadboard
Temp/Hum Sensor

This is how this translates into the Fritzing breadboard view
Temp/Hum Fritzing

The script calls the Adafruit C-code with the parameters 22 (for the sensor type) and 4 (which is the GPIO pin to be used). As even this code is not able to perform a successful measurement at every run I created a small loop to ensure that the logging only happens when the values have been extracted successfully. You may also notice the counter variable in the code, this variable can be used to track how many loops are required until a successful measurement could be taken. In practice the values are between 2 and 5 loops, maximum I noticed so far was 11.

#!/usr/bin/perl

# logfile handling
sub logging {

  my $logfile = "/appco.de/log/appco.de.log";

  if ( ! open LOG, ">>", $logfile ) {
    die "Kann Logdatei nicht anlegen: $!";
  }

  my ($sekunden, $minuten, $stunde, $tag, $monat, $jahr) = localtime;
  my $echtes_jahr = $jahr + 1900;
  my $echter_monat = $monat + 1;
  printf LOG "%s.%02s.%02s %02s:%02s:%02s %s\n", $echtes_jahr, $echter_monat, $tag, $stunde, $minuten, $sekunden, $_[0];
  close LOG;

}

my $bin = './Adafruit_DHT 22 4';
my $check = 0;
my $counter = 0;

#run until a temperature and humidity value has been logged
while ($check == 0){
  # run the C program
  $result2 = `$bin`;

  # extract the strings
  my @array = split("\n", $result2);

  $counter = $counter + 1;

  # logging only if the string is not empty
  if ($array[2] ne "") {
    &logging ("$array[2]");
    &logging ("$counter");
    $check = 1;
  }
}

PIR sensor

As I would like my HomeAutomation to learn my schedule I need to give the Pi some eyes. Let’s start with a PIR (passive infrared) sensor.
The Fritzing screenshot below shows how the sensor is wired up to the cobbler. Basically the red wire goes to 5V0, the black wire to GND and the yellow data wire is hooked up to #25.

PIR Fritzing

As an initial test the following statement executed from the command line served me well

while true; do gpio read 6; done

This reports a 0 when the PIR is not triggered and a 1 when triggered.

As a next step I replicated the very same functionality in a basic perl script using WiringPi-Perl.

#!/usr/local/bin/perl -w</code>

use lib "/appco.de/WiringPi-Perl";

require "wiringpi.pm";

if (wiringpic::wiringPiSetup () == -1)
{ exit 0};

# set pin #6 (marked with #25 on the T-Cobbler) to mode INPUT
wiringpic::pinMode (6, 0);

while (1){
  # read from PIR

  # PIR not triggered
  if (wiringpic::digitalRead (6) == 0){
    print ("off \n");
    wiringpic::delay (500); # milliseconds
  }

  # PIR triggered
  if (wiringpic::digitalRead (6) == 1){
    print ("on \n");
    wiringpic::delay (500); # milliseconds
  }
}

This code writes “off” to the standard out when the PIR is not triggered and “on” when triggered until you stop the script with ctrl+c.

Blink LED in WiringPi-Perl

I reworked the script from yesterday “Preparing the GPIO basis” using the WiringPi-Perl wrapper.

#!/usr/local/bin/perl -w

use lib "/appco.de/WiringPi-Perl";

require "wiringpi.pm";

if (wiringpic::wiringPiSetup () == -1)
{ exit 0};

# set pin #0 (marked with #17 on the T-Cobbler) to mode OUTPUT
wiringpic::pinMode (0, 1);

while (1){
  # LED off
  wiringpic::digitalWrite (0, 0);
  wiringpic::delay (500); # milliseconds

  # LED on
  wiringpic::digitalWrite (0, 1);
  wiringpic::delay (500); # milliseconds
}

While digging into the details I found a quite useful overview of the function wrappers in the file ../WiringPi-Perl/wiringpi.pm

package wiringpi;

*wiringPiSetup = *wiringpic::wiringPiSetup;
*wiringPiSetupSys = *wiringpic::wiringPiSetupSys;
*wiringPiSetupGpio = *wiringpic::wiringPiSetupGpio;
*wiringPiGpioMode = *wiringpic::wiringPiGpioMode;
*pullUpDnControl = *wiringpic::pullUpDnControl;
*pinMode = *wiringpic::pinMode;
*digitalWrite = *wiringpic::digitalWrite;
*pwmWrite = *wiringpic::pwmWrite;
*digitalRead = *wiringpic::digitalRead;
*shiftOut = *wiringpic::shiftOut;
*shiftIn = *wiringpic::shiftIn;
*delay = *wiringpic::delay;
*delayMicroseconds = *wiringpic::delayMicroseconds;
*millis = *wiringpic::millis;
*serialOpen = *wiringpic::serialOpen;
*serialClose = *wiringpic::serialClose;
*serialPutchar = *wiringpic::serialPutchar;
*serialPuts = *wiringpic::serialPuts;
*serialDataAvail = *wiringpic::serialDataAvail;
*serialGetchar = *wiringpic::serialGetchar;
*serialPrintf = *wiringpic::serialPrintf;

Preparing the GPIO basis

To use GPIO with perl on the RaspberryPi the following installations are necessary:

  1. C library for Broadcom BCM 2835 from http://www.open.com.au/mikem/bcm2835
  2. BCM2835 perl library from CPAN http://search.cpan.org/~mikem/Device-BCM2835/lib/Device/BCM2835.pm

To install the C library for Broadcom BCM 2835 the following steps are required:

wget http://www.open.com.au/mikem/bcm2835/bcm2835-1.17.tar.gz
tar zxvf bcm2835-1.17.tar.gz
cd bcm2835-1.17
./configure
make
sudo make test
sudo make install

For the BCM 2835 perl library the installation works as outlined below:

wget http://search.cpan.org/CPAN/authors/id/M/MI/MIKEM/Device-BCM2835-1.6.tar.gz
tar –xvfz Device-BCM2835-1.6.tar.gz
perl Makefile.PL
make
sudo make test
sudo make install

To verify the functionality I used the following test bed

Blink LED Breadboard

Blink LED Schaltplan

I used the example script from http://elinux.org/RPi_Low-level_peripherals#GPIO_Driving_Example_.28Perl.29

#!/usr/bin/perl

use Device::BCM2835;
use strict;

# call set_debug(1) to do a non-destructive test on non-RPi hardware
#Device::BCM2835::set_debug(1);
Device::BCM2835::init()
|| die "Could not init library";

# Blink pin 11:
# Set RPi pin 11 to be an output
Device::BCM2835::gpio_fsel(&amp;Device::BCM2835::RPI_GPIO_P1_11,
&amp;Device::BCM2835::BCM2835_GPIO_FSEL_OUTP);

while (1){
  # Turn it on
  Device::BCM2835::gpio_write(&amp;Device::BCM2835::RPI_GPIO_P1_11, 1);
  Device::BCM2835::delay(500); # Milliseconds
  # Turn it off
  Device::BCM2835::gpio_write(&amp;Device::BCM2835::RPI_GPIO_P1_11, 0);
  Device::BCM2835::delay(500); # Milliseconds
}

This script lets the LED blink for 500 milliseconds and continues to run until you stop it with ctrl+c.

Blink LED Wiring

WiringPi Perl

I had some problems with the compilation of Wiring Pi Perl, here is how it worked out for me:

Get the clone from github
git clone git://github.com/WiringPi/WiringPi-Perl.git

This will get you a directory named
WiringPi-Perl

When I tried to compile WiringPi-Perl by using the script
./build.sh
I faced some errors.

It turned out that the link to the perl library needed to be modified from
/usr/lib/perl/5.10.1/CORE to /usr/lib/perl/5.14.2/CORE to match my system.

In addition the sub-directory WiringPi was empty, to fix that I simply cloned wiringPi into the directory
git clone git://github.com/WiringPi/WiringPi.git

This left me with one final error: a missing WiringPi/wiringPi/serial.h
I checked the directory and found a wiringSerial.h.
So I created my own serial.h with cp wiringSerial.h serial.h

With these modifications the compilation completed without any issues.

I did not test it yet, but will try it out soon.