I have been experimenting a bit with home automation lately by hooking up some small electrical relays to my Raspberry Pis. So far I have my bedroom fan and a small lamp fully under remote control and connected to my home network. I even have them under voice control now by using an app called Tasker on Android, as well as two helper plugin apps for Tasker called Autovoice and an associated SSH Plugin. I feel an undeniable sense of power whenever I verbally tell my phone to turn my lamp or fan on or off, and it has quickly become a much more natural and pleasant feature of my bedroom over the last few days.

In the past, I have always used Python and a GPIO control library to control the output pins on a Raspberry Pi. This method requires installing both Python and the pin control library on a fresh Raspbian or Retropie install, which can be a bit of a nuisance.

Since the release of the first Raspberry Pi I've been wanting a simple solution to just turn Raspberry Pi pins on or off without having to install any additional software or remember any commands. I've also loved bash scripting for a long time now, and while putting together my last minimal Pi Zero clock project I realized that a pi's output pins can be fully controlled by writing to system files without the need of installing Python or anything else. For example, to turn on pin 26 on a Raspberry Pi one can simply enter these three short commands:

sudo echo "26" > /sys/class/gpio/export
sudo echo "out" > /sys/class/gpio/gpio26/direction
sudo echo "1" > /sys/class/gpio/gpio26/value

Turning the pin off is as easy as echoing a value of 0 to the pin's value in the same location as the last line.

I first created a number of small scripts to turn certain pins on, and another script to turn the same pin off and was using that with my home automation system. After a couple of days, I decided that I'd like to have a script to toggle the state of any arbitrary pin. This is so that I can issue the same command to turn my lamp on or off without having to be specific about what I want when I yell at the phone. I also wanted this script to be able to specifically turn a pin on or off in the case that I'm not at home and want to make sure something is turned on or off even if I don't recall whether I left it on or not. I quickly came up with the following bash code that accomplishes just that:

#!/bin/bash
# A utility script to toggle a raspberry pi gpio pin on or off
# Spike Snell - July 2017

# If there are command line options to use
if [ $# != 0 ]
then

    # Set up our argument variables
    arg1="$1"
    arg2="$2"

    # If the gpio pin was not previously set up
    if [ ! -e /sys/class/gpio/gpio"$arg1" ];
    then
        # Make sure that gpio pin $arg1 is initialized
        echo "Initializing gpio pin" $arg1
        echo "$arg1" > /sys/class/gpio/export
        echo "out" > /sys/class/gpio/gpio"$arg1"/direction
    fi

    # Check to see if there was a second command line argument
    if [ -z "$2" ]
        # Argument 2 for the on/off value was not set
        # We should just toggle the current state of gpio pin $arg1
        then
             # If the current value is 1 set it to 0 and vice versa
             if grep -q 1 /sys/class/gpio/gpio$arg1/value
             then
                echo "Toggling gpio pin" $arg1 "to 0"  
                echo "0" > /sys/class/gpio/gpio"$arg1"/value
             else
                echo "Toggling gpio pin" $arg1 "to 1"
                echo "1" > /sys/class/gpio/gpio"$arg1"/value
             fi
        # Argument 2 for the on/off value was set
        # We should set gpio pin $arg1 to the value of $arg2
        else
             echo "Setting gpio pin" $arg1 "to" $arg2
             echo "$arg2" > /sys/class/gpio/gpio"$arg1"/value
        fi

# Else there were no options passed in, let the user know about them
else
    echo "Please enter what pin to toggle, ex: sudo ./pin.sh 11"
    echo "Optionally enter if the pin should be 1 or 0, ex: sudo ./pin.sh 11 0"
    echo " * Make sure to run as super user "
fi

I included some helpful information near the bottom that gets displayed if the script is called without any parameters. To use it the script should be saved as pin.sh and set to be executable with the command sudo chmod +x pin.sh.

I plan to use this script quite a lot in the future and this seems a good place to keep a copy of it. Hopefully this can be helpful to others as well. Feel free to leave any comments or suggestions that you may have.

I was inspired by this post on Hackaday where Setvir created an elegant single LED clock using an Arduino Pro Micro. I'm more of a fan of Raspberry Pi's and have been wanting to come up with a simple single LED clock design of my own ever since reading that article.

It occurred to me today that the Pi Zero's status light could be commandeered for this purpose which would eliminate the need for any other additional parts. I considered using Python for this but eventually decided upon using bash scripting as it is already baked in to most common Pi Zero images such as Raspbian or Retropie.

The heavily commented code below is what I came up with to bring this clock design to life:

#!/bin/bash
# A minimalist led clock for the Pi Zero ( And Pi Zero W )
# Uses only the onboard led to blink the current hour
# And then to quickly blink the the tens place of minutes
#
# Spike Snell - June 2017

# First set the trigger for the onboard green led to none so that we have control of it
echo none | sudo tee /sys/class/leds/led0/trigger

# Turn off the led so that we have a known state to start
echo 1 | sudo tee /sys/class/leds/led0/brightness

# Loop endlessly
while true
do

    # Wait for a full second to seperate our visual count
    sleep 1

    # Loop for the current number of hours
    # Trim leading 0's so that 08 and 09 aren't interpreted as an octal base
    for ((n=0;n<$(date +"%I" | sed 's/^0*//');n++)) 

    do

        # Wait a bit 
        sleep .25

        # Turn the led on
        echo 0 | sudo tee /sys/class/leds/led0/brightness

        # Wait a bit
        sleep .25

        # Turn the led off
        echo 1 | sudo tee /sys/class/leds/led0/brightness
   
    done

    # Wait for a half second
    sleep .5

    # Now loop very quickly for the current first tens digit of minutes
    for ((n=0;n<$(date +"%M" | head -c 1);n++))

    do 

        # Wait for a small bit
        sleep .1

        # Turn the led on
        echo 0 | sudo tee /sys/class/leds/led0/brightness

        # Wait for a small bit
        sleep .1

        # Turn the led off
        echo 1 | sudo tee /sys/class/leds/led0/brightness

    done

done

I saved the script in my home directory as minimalistClock.sh and made it executable with the command chmod +x minimalClock.sh. It is then run under its own screen with the command screen ./minimalClock.sh since it can be somewhat distracting if running on your main session due to all the echo commands. Screen is also a very handy way to make the clock persist and keep running even after logging out of your current session. Use the command sudo apt-get install screen if you don't already have it installed. After getting the clock up and running in screen you can press ctrl+a then ctrl+d to detach the screen and have it keep running in the background.

The clock is read by counting the number of long blinks to get the hours, and then the number of short blinks to get the tenth place of minutes. For example, 4 longer blinks followed by 3 shorter blinks indicates that the current time is about 4:30. I decided not to use a 24 hour military format for this because that would end up being far too many blinks when late in the day.

This script can be easily added to /etc/rc.local so that it will begin running when the Pi starts up.

This is exactly the minimalistic clock that I have been desiring for so long and it looks great running in my translucent Pi Zero Tic Tac Case which I have attached to the wall. Let me know what you all think of this basic clock design. If it could be made even simpler in some way I would love to experiment with that.

-- Edit March 2018

I have edited the code slighty in order for it to work on a Raspberry Pi 3 B+ ( Probably the non-plus version as well ).

Same idea as before, but this time using the onboard status led on the back of the bigger Pi. For some reason the light/dark values all had to be reversed, but other than that the code is the same. I found that putting a piece of electrical tape over the red led ( Which is always on when the Pi is receiving power ) makes the clock a lot more pleasant to leave on.

#!/bin/bash
# A minimalist led clock for the Pi 3 B+
# Uses only the onboard green led to blink the current hour
# And then to quickly blink the the tens place of minutes
#
# Spike Snell - March 2018

# First set the trigger for the onboard green led to none so that we have control of it
echo none | sudo tee /sys/class/leds/led0/trigger

# Turn off the led so that we have a known state to start
echo 0 | sudo tee /sys/class/leds/led0/brightness

# Loop endlessly
while true
do

    # Wait for a full second to seperate our visual count
    sleep 1

    # Loop for the current number of hours
    # Trim leading 0's so that 08 and 09 aren't interpreted as an octal base
    for ((n=0;n<$(date +"%I" | sed 's/^0*//');n++)) 

    do

        # Wait a bit 
        sleep .25

        # Turn the led on
        echo 1 | sudo tee /sys/class/leds/led0/brightness

        # Wait a bit
        sleep .25

        # Turn the led off
        echo 0 | sudo tee /sys/class/leds/led0/brightness
   
    done

    # Wait for a half second
    sleep .5

    # Now loop very quickly for the current first tens digit of minutes
    for ((n=0;n<$(date +"%M" | head -c 1);n++))

    do 

        # Wait for a small bit
        sleep .2

        # Turn the led on
        echo 1 | sudo tee /sys/class/leds/led0/brightness

        # Wait for a small bit
        sleep .2

        # Turn the led off
        echo 0 | sudo tee /sys/class/leds/led0/brightness

    done

done

I have created a very simple Raspberry Pi Zero W case using a Tic Tac container. I considered putting the full instructions here but decided that Instructables would be the best platform for it to get mass exposure and the best search engine indexing. The plans have been released into the public domain.

Check out the 5 simple steps to make my super low cost Pi Zero W case here.