How to save power by adding a PIR motion sensor to your Raspberry Pi digital picture frame 2

How to save power by adding a PIR motion sensor to your Raspberry Pi digital picture frame

If you want to bring down the power consumption of your digital picture frame to a minimum, you can use motion sensors that make the screen only power on only when a carbon-based life form (which includes your dog or cat) is detected.

In this article, I will show you how to add a passive infrared (PIR) sensor to your digital picture frame project, including the hardware and the software that you need.

I will also discuss some limitations of motion sensors, so that you can decide for yourself if they are suitable for your use case.

What is a motion sensor?

A motion sensor detects moving objects using different approaches and technologies. The most obvious example is a sliding door that opens when you approach. But they are also used in hand dryers sensing your hand movement, home alarm systems, and many more devices that you probably use every day.

There are active and passive motion sensors with tomographic, microwave and ultrasonic sensors for different types of tasks and precision.

The most widely used type in home systems is the passive infrared (PIR) sensor. A PIR sensor is designed to detect the infrared radiation, i.e. the heat pattern, emitted naturally from a human body.

PIR sensors are a favourite among Raspberry Pi home brewers as they allow many exciting use cases.

If you are interested in knowing more about the technology, read about it on the Adafruit website or watch Andreas Spiess’ video below.

Motion sensors in digital picture frames

The integration of motion sensors into digital picture frames is quite popular. This way, you can make sure that only when a person is actually looking at the frame, the screen is turned on. Or at least a person is in the room who may be looking at the photos. Or your dog who is looking for you..

Many off-the-shelf photo frames include motion sensors, like the Nixplay series, the Netgear Meural Canvas II, or the FRAMEN Player. Normally, they are easy to spot on the frame.

So let me show you how you can add a PIR motion sensor to your do-it-yourself photo frame project.

The PIR infrared sensor

PIR motion sensors are very cheap and come at around 3€/$. As they are such low-value items, they are often resold in packs of three or five. I would suggest that you pick a pack of three as the sensors don’t seem to be of very high built quality and may be dead on arrival in some cases if you believe the comments section on Amazon. Or people just got the wiring wrong.

I had ordered a PIR sensor because a Canadian reader of this blog had some issues with the instructions he had used and had asked for help. Given how cheap they are, I thought that this would be a good opportunity to give it a try myself and document the steps to get it going with a digital frame setup.

As for the choice of the right sensor for you, I recommend again one of Andreas’ videos where he also introduced recent new PIR sensor form factors.

I got myself the HC-SR501 which seems to be the basic pleasure model of PIRs. There are various manufacturers for the same thing, mine was from DAOKI.

There are basically two types that you will find. A lengthy one, which is much smaller, and a square one. Both do the job. Which one you take depends on your hardware installation and the space that you have available.

When it arrived, I was surprised how big the sensor, i.e. the white housing, actually was.

How to save power by adding a PIR motion sensor to your Raspberry Pi digital picture frame 3
How to save power by adding a PIR motion sensor to your Raspberry Pi digital picture frame 4

The white dome is over a square centimeter in size. The sensor itself is much smaller but it needs the little dome to spread the infrared rays evenly in all directions.

If you want to integrate a PIR sensor into your photo frame, you should opt for the lengthy version which has a much smaller dome.

What else you need

You also need a cable called “Dupont Wire” with female connectors on both ends that you slide on the pins of both the Raspberry Pi and the PIR sensor.

This cable needs to be long enough to reach from the place where you choose to install the motion sensor, often in the middle of the bottom part of the frame, to the place where you have your Raspberry Pi installed. So don’t get it too short. You need three of them.

The PIR sensor is connected to the Raspberry Pi on the GPIO pins. These are the 2×20 pins on your Raspberry Pi board, no matter which full-size Pi version you have. If you have the Raspberry Pi Zero, you will need this.

The PIR sensor comes without a data sheet, but for the model I am using, you can download it here.

How to connect cables to the PIR sensor

The PIR sensor has three pins. On the HC SR-501 they are:

  • VCC (5 Volt Power)
  • OUT (Control Channel)
  • GND (Ground)
How to save power by adding a PIR motion sensor to your Raspberry Pi digital picture frame 5

Important note: I have seen PIR sensors where this order was inverted, so always get a data sheet for your particular sensor or look closely at the circuit board. In my case, I had to take the dome off to see the labeling.

I read that if you get it backwards you won’t damage the PIR sensor but it won’t work, but I can’t vouch for this!:

Ideally, you have a black, a red, and a green-colored wire. Connect the black one to GROUND, the red to VCC, and the green one to OUT. These are the standard colors often used and will help you not mixing up the pins.

There are two potentiometers on the sensor circuit board which control the time delay and the sensitivity. Check on your data sheet which one is which.

How to save power by adding a PIR motion sensor to your Raspberry Pi digital picture frame 6

In our case, the time delay will be controlled with our script but you may adjust the sensitivity settings according to your needs.

How to connect cables to the Raspberry Pi GPIO pins

The GPIO connector are used for any non-USB or HDMI outside connection. They are great for attaching buttons, cameras or LEDs to build robots, surveillance devices and other kinds of gadgets.

Matt Hawkins has an excellent photo on his website which makes it very easy to understand:

How to save power by adding a PIR motion sensor to your Raspberry Pi digital picture frame 7

If you want to read more about the GPIO pins, the official Raspberry Pi site has got you covered.

Power down your Raspberry Pi, remove the power supply and attach the cables coming from the sensor like this:

Connect the red VCC cable to the 5 Volt power Pin 2, the black GROUND cable to ground Pin 6, and the green cable to the control Pin 11.

Power it up again and do a test run. Connect to your Pi via Terminal and enter

sudo nano testpir.py

Copy and paste the following lines into the editor window:

#!/usr/bin/python

import time
import datetime
from gpiozero import MotionSensor

pir = MotionSensor(17) #GPIO number here

while True:
    pir.wait_for_motion()
    if pir.motion_detected:
        print("Somebody is moving")
        print (datetime.datetime.now())
        time.sleep(0.1)

Hit CTRL+O to save the file and CTRL+X to exit.

Turn the PIR sensor away from you and enter

python3 testpir.py

Now wave your hand in front of the sensor.

The Terminal window should now display “Somebody is moving!” and the current time.

If everything works, hit CTRL-C to stop the script execution and skip the next paragraph.

Note: You may want to use the testpir.py script later once more to fine-tune the sensitivity settings of the PIR sensor.

If it doesn’t work at first..

As always, there can be a number of reasons.

  • Check the wire connections on the Raspberry Pi side.
  • Check the pins on the PIR sensor. You may have a model where the Pins are inverted. In that case, swap the red and the black cable.
  • Check the python script. Is there any error message in the Terminal?

The python script to turn your monitor on and off depending on human movement

All we need is one simple Python script what will run in a loop.

Create a new file with

sudo nano motionsensor.py

Copy and paste the following lines into the editor window:

#!/usr/bin/python

import sys
import time
import RPi.GPIO as io 
import subprocess

io.setmode(io.BOARD)
DARK_DELAY = 10 #this is where you define after how many seconds you want the display to go dark when there is no motion detected
PIR_PIN=11 #if you connect to another pin, specify here

def main():
    io.setup(PIR_PIN, io.IN)
    turned_off = False
    last_motion_time = time.time()
    while True:
        if io.input(PIR_PIN):
            last_motion_time = time.time()
            sys.stdout.flush()
            if turned_off:
                turned_off = False
                turn_on()
        else:
            if not turned_off and time.time() > (last_motion_time + DARK_DELAY):
                turned_off = True
                turn_off()
            if not turned_off and time.time() > (last_motion_time + 1):
                time.sleep(.1)
def turn_on():
    CONTROL = "vcgencmd"
    CONTROL_UNBLANK = [CONTROL, "display_power", "1"]
    subprocess.call(CONTROL_UNBLANK)

def turn_off():
    CONTROL = "vcgencmd"
    CONTROL_BLANK = [CONTROL, "display_power", "0"]
    subprocess.call(CONTROL_BLANK)

if __name__ == '__main__':
    try:
        main()
    except KeyboardInterrupt:
        io.cleanup() 

Hit CTRL+O to save the file and CTRL+X to exit.

Now start the script with

python3 motionsensor.py

and hopefully it works!

Running the motion sensor script as a service

I would recommend to autostart this script as a service with systemd rather than using crontab. You can read more about this approach in my article here.

Open a new file with

sudo nano /etc/systemd/system/motionsensor.service

An empty editor window will come up. Copy and paste this text into the window:

[Unit]
Description=MotionSensor Service
After=multi-user.target

[Service]
Type=idle

User=pi
ExecStart=/usr/bin/python3 /home/pi/motionsensor.py

Restart=always
RestartSec=60

[Install]
WantedBy=multi-user.target

Save the file and change the permissions to make it readable by all.

sudo chmod 644 /etd/systemd/system/motionsensor.service

As the last step, you need to tell the system that you have added this file and want to start the service every time your Raspberry Pi boots up.

sudo systemctl daemon-reload
sudo systemctl enable motionsensor.service

Reboot your Pi and check with

ps -ef | grep python

if the process is running as expected.

Limitations of PIR sensor motion detectors

Although motion detectors are often called “presence detectors”, that’s not what they do. A PIR sensor motion detector requires movement (and heat).

If you enter your living room, sit down on the couch and calmly read with a Kindle with only a gentle tapping of your fingers, a digital picture frame with a motion detector on the other side of the room might forget that you are there.

But its usefulness really depends on your particular use case.

For example, it makes a lot of sense for a Magic Mirror installation as you stand right in front it to read messages or calendar appointments.

But with a digital picture frame, this may not be so reliable, as you are often looking from a distance. But I may be completely wrong as the leading manufacturer of digital picture frames, Nixplay, includes them with all its frames, so there is customer demand for it. And whatever helps to lower the power consumption of electronic devices without making it inconvenient is great.

By the way, if you want to increase the precision of your sensors and reduce the number of false positives, you can combine two of them with an AND command.

Conclusion

So there you have it, a low-cost and easy to install motion sensor for your DIY photo frame. You may want to fine-tune the sensor sensitivity with the variable resistor to make it trigger the screen commands just like you want it.

Let me know what your experiences with motion sensors are!

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