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Raspberry Pi based Automatic Cat Feeder

14.08.2016

We have a cat, and more than a few times per year find ourselves leaving home for a few days without it. Now usually we ask neighbors or friends to feed it, but that's hardly over-engineering the problem. With the ubiquity of modern computers, why not automate the process, and get more information than you could ever want while at it? This project started with some experimenting on the first generation of Raspberry Pi, mainly to learn what new fun things could be done with a Linux distribution stuffed in such a small form factor. The answer is a whole lot! Much of the experience I gained from this project is being used further in my next ROV project.

Cat feeder overview

The features I wanted from the automatic cat feeder were automatic feeding (of course), temperature measurement, web camera, power outage detection, and logging of various events. I also wanted all of this information to be available no matter where I was on the planet, which meant Internet access. To achieve all of this, I implemented a web-server on the Raspberry Pi, from which regular users can monitor all permitted data. Super users can log in via a password and user, and access a maintenance menu. The feeding sequence was setup using the UNIX app Cron. What Cron does is check a special crontab file, and execute jobs listed there. This is done according to a time schedule defined in the crontab file itself. Jobs can be executed either cyclically, or on special dates. Control of hardware functions is done via a specially made board I designed, which has an on-board temperature sensor, an external sensor, Real Time Clock, 5V power converter, and several hobby servo control outputs. Mechanical parts were designed in OpenSCAD, and printed using my 3D printer.

Cat feeder internal view

Software

A major part of this project was the software to control it all. The basic architecture is a number of independent scripts which can all be monitored or modified by a web-server. The PHP web-server is the user interface, displaying available data and also starting/stopping certain scripts. The main functions of the feeder (feeding and motion capture) are handled by operating system scheduled tasks in the case of feeding, which is controlled by crontab, and an independent script which places motion capture images in a folder available to the web-server. The software was written a long time ago, and with several iterations, so my explanation of how it works may be lacking. I have tried to include all of the relevant source files, however various permissions and other settings aren't as easy to include in a zip file. Some hacking will probably be required to get everything working from scratch. All source code can be found here.

Web-server

For the web-server I installed lighttpd, with php. I followed the tutorial provided here, which was quite useful: Running a lightweight webserver on the Raspberry Pi (lighttpd) In addition, I also had to allow the www-data user permission to use the camera, and I2C bus:

sudo adduser www-data video
sudo adduser www-data i2c

and full rights to the folder where motion captures are dropped. The pi user is running the motion capture script, because of the way I had setup a virtual environment for OpenCV. Scripts, and user rights are explained below. A username and password prompt has been placed on the website to allow an admin to change the feeding frequency, delete motion captures, update the RTC time and various other maintenance functions. The web-page appears like this to a user who is logged in.

Crontab editing

To allow the web-server to set and change when to feed a portion, I wrote some php code to automatically update the crontab with new information. There is plenty of information on how crontab works elsewhere on the Internet, so I'll redirect you here if you're unfamiliar with crontab: CronHowto. Quite simply, the php code gets the desired number of portions per day, calculates a feeding interval, and writes it to crontab after first clearing all old crontab entries. The www-data user shouldn't have any other cronjobs listed, so clearing the entire list before adding a new entry is safe in this case. Keep this mind if you plan on adding other entries to the crontab!

// Clear all crontab jobs
shell_exec('crontab -r');
// Enter command
shell_exec('(echo "0 */' . $feedingInterval . ' * * * /var/www/feed_portion.sh") | crontab -');

Motion Detection

Motion detection is done using OpenCV, in a python script. I basically followed the tutorial here; "Home surveillance and motion detection with the Raspberry Pi, Python, OpenCV, and Dropbox" and modified the code to better fit the intended application. As mentioned in the tutorial, as virtual environment is created and used for OpenCV. Perhaps not necessary, but I did it for the sake of correctness. To ease starting and stopping the motion capture I created a script which loaded the required environment, booted the python script with the right argument, and deactivated the environment once complete. To make this script run at boot, I created an init script for it which can be seen below. I followed the instructions on this page for how to create the script, register the correct permissions, and enable activation at boot time. Raspberry Pi - run program at start-up

#!/bin/bash
# /etc/init.d/motionCapture

### BEGIN INIT INFO
# Provides:          motionCapture
# Required-Start:    $all
# Required-Stop:     $remote_fs $time
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
# Short-Description: Motion Capture
# Description:       This service detects motion and saves images.
### END INIT INFO


case "$1" in 
    start)
        echo "Starting motionCapture"
        /bin/su pi /var/www/pi_surveillance_script
        ;;
    stop)
        echo "Stopping motionCapture"
        killall python
        ;;
	still)
        echo "Grabbing still image"
		killall python
		/bin/su pi /var/www/pi_still_script
		/bin/su pi /var/www/pi_surveillance_script
        ;;
    *)
        echo "Usage: /etc/init.d/motionCapture start|stop|still"
        exit 1
        ;;
esac
exit 0

What the init script does is provide a standard way for the operating system to work with subsystems at boot time. It also provides a convenient way to run a service. In the script above I start the surveillance script as the pi user with the "start" argument. Stopping the script is done by killing all python threads. This is only acceptable in this system because the motion capture is the only python process which runs the entire time. However, if the "stop" command were issued when one of other python scripts were running, then it would stop the other script as well! In practice this will happen very rarely. The grab still image command "still" stops the motion capture, takes a still image, and then starts the normal motion capture again. To get this to work when called by the web-server, I had to edit the "sudoers" file and add the following entries:

www-data ALL=NOPASSWD: /etc/init.d/motionCapture
www-data ALL=NOPASSWD: /var/www/pi_still_script<
www-data ALL=NOPASSWD: /var/www/pi_surveillance_script
www-data ALL=NOPASSWD: /sbin/shutdown

This allowed the web-server to run the following scripts without needing to provide a password. The shutdown command does not relate to the motion capture, but is something I used to safely shut down the system from the web interface.

Various Scripts

The other scripts found in the source folder should be pretty self-explanatory. Let me know if any are confusing, and I'll write about them here.

Hardware

The hardware in this project is pretty basic, and can be simplified even further. If sensory input is of no concern, then it can be reduced to just a servo signal board, and a power supply. However, in the spirit of keeping things over-complicated I elected to include all of the senors mentioned above. And of course, the feeding mechanism itself would require a custom design.

Specialized Mechanical Parts

Surprisingly, the feeding mechanism turned out to be a major design issue, requiring several iterations, and delaying this projects completion by almost 1 year. Initially I had envisioned a feed auger, as this it both mechanically simple, and has been used before by similar projects, seemingly with great success. In my experience however it was prone to jamming, something I was never able to remedy. I tried altering the pitch of the auger screw blades, the diameter, the strength of motor, but all to no avail. I eventually gave up when the motor I had installed was stronger than the 3D-printed auger, causing it to break and release pieces of plastic into the food. This left me less than impressed, so I decided to rethink the issue.

Broken auger

After playing with cat kibble for a while, I tried something simpler, and perhaps more intuitive. Simply shoving the food out of the pipe when required. This required slightly more complicated machinery behind the scenes, but the sections exposed to the cat food could be simpler and more robust. All in all, the new design should in theory be very difficult to break in a way which releases small plastic pieces into the food, and difficult to jam. Tests later confirmed this, and I'm quite happy with the results. The only drawback over a regular auger design is an increase in moving parts, and no implicit "locking" of the food. I.e. tilting the feeder will release food as the design relies on friction between the kibble itself to prevent all of the feed from pouring out at once. Other than the feeding mechanism, there were not many complicated parts needed. I have provided OpenSCAD files which may or may not be easy to alter to fit different sized parts, see it on Thingiverse here. The pipe clamps were generated using this thingivser model: Pipe clamps

To run the feeding mechanism a continuous rotation servo is used. In hindsight a geared DC motor would have worked much better, as the piston based design has no need for motor reversal, or changes in speed. In fact, the use of a servo signal is problematic when trying to stop the motor, and the current implementation will make a low buzzing noise when not active. Considering that the motor only runs for about 10 seconds twice a day, having it continuously idle is not favorable.

Food pusher Food pusher detail Piston and arm

I2C Interface Board

The purpose of the I2C interface board is the following:

Interface board close up, sitting on raspberyy pi

Power is provided by a LT3995 based buck converter, which steps voltages up to 32 volts down to 5V regulated DC. This is then used to power the interface board, and also injected directly into the raspberry pi header to power the pi directly (thus avoiding the use of a large USB cable). Whether this still works on newer (> version 2) Raspberry Pies I am unsure. Because of the 5V standard servo output, the ATmega controller runs at 5V also. The I2C interface of the raspberry pi, and temperature sensor both run at 3V3, so a 2N2007 based level converter is used between them. The purpose of the ATmega is to translate 1-wire temperature sensor inputs to I2C, create servo signals controllable via I2C, and monitor the level of food in the hopper. The specific chip used was a ATMEGA328. The internal temperature is monitored by a MCP9808 temperature sensor, which sits directly on the I2C bus. The MCP79410 serves as the real-time clock and power up/down timer, and is also connected directly to the I2C bus. A small button cell battery is used to keep the time when not externally powered. Eagle design files and firmware can be downloaded here.

Final Thoughts

Some general notes on what I've encountered using the feeder so far:

Food dislodger

Notes for future feeder projects:
Motion captures

The motion capture function has been the most exciting feature of this project, so far it shows that neighbor cat very seldomly drop by to steal food, whereas magpies will try at every chance they get. It's also a great way to check when the cat last ate.

Neighbor cat Magpie
Tastes good! Draw me like one of your french girls

Similar projects and inspiration

I'm not the first to make a fancy cat feeder, so these projects for other great ideas!

DIY Cat Feeder v2
Pet Feeder
Automatic Cat Feeder
Barley Cat
RFID Cat Door


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Disclaimer: I do not take responsibility for any injury, death, hurt ego, or other forms of personal damage which may result from recreating these experiments. Projects are merely presented as a source of inspiration, and should only be conducted by responsible individuals, or under the supervision of responsible individuals. It is your own life, so proceed at your own risk! All projects are for noncommercial use only.


Creative Commons License This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported License.


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