Introduction: Stand Alone Pet Feeder for 20 Liters of Pellets / Nuggets

What I need is a pet feeder

  • which has a big volume for pellets / nuggets and feeds my cats even during a long vacation of 2 months.
  • which is really robust and reliable, so I can be sure that my cats don't die during my vacation.
  • which keeps functioning after a power failure.
  • which does not require a 3D printer (makerbot).

Step 1: A Chinese Pet Feeder Which Is NOT Reliable

I have this pet feeder from China but it is not worth the money:

  • It works only on battery which is a stupid design.
  • The batteries cannot be replaced with a DC power supply because the microprocessor will forget any programmed hours after a power failure.
  • The mechanics are very cheap. A tiny motor moving small plastic gears which are placed in a an unintelligent location where they get clogged by the pellet poweder and I saw them getting stuck!
  • It has a mechanical sensor (detecting the position of the ejection wheel) which also gets dirty by pellet poweder and then the feeding motor never stops throwing pellets!
  • The volume of the pellet container is too small. Maximum 3 weeks of feeding 2 cats.
  • The programming of the feeding hours is so extremely clumsy that you will never be able to do it if you ever lose the (horrible chinese) manual.
  • This device is just cheap crap.
  • Simply do not buy it!

Also here on Instructables are several pet feeders but none meets my criteria.

Step 2: Using a Modified Meat Grinder

So I constructed my own machine based on a meat grinder (approx US $38).

Step 3: Modify the Helix

The helix has a pivot of steel and a helix of aluminum. The last turn must be removed with an angle grinder.

Step 4: Modify the Plate

Then prepare the meat outlet grid like this. This is an extremely hard steel which you must cut with an angle grinder.

Step 5: Modify the Attachment

The attachment does not have a smooth surface. To avoid that pellets get destroyed I inserted a smooth metal sheet.

Step 6: Mounting Together

All mounted together.
(My cat is so curious)

Step 7: Take Out the Guts of the Machine

Here you see the motor which runs very fast and the gear box (black) which makes the helix turn much slower.

Don't worry about the switches. (One for turning on/off and one for foreward/backward rotation) I let them connect as they are.

Step 8: The Wooden Box

To mount the box I use plywood, 15 mm thick.
My box is 30 cm x 40 cm x 1,20 m.
Obviously you can chose another size if you like.
You need 3 wooden "floors" and a lid.

Step 9: The Electronics

The electronics is very simple. I use an Arduino Nano which is very cheap.
The Nano allows to be fed with 5V over the USB cable or over an external power supply of 8V to 25V or both at the same time.

Step 10: Mounting the Circuit

The electronics is mounted at the back side which has a hole at the height of the USB plug. So it is easy to later change the programming without the need to open the box.

Step 11: The Arduino Code

The sketch can be programmed to feed at certain hours. (once, twice,... per day)
In my programming at 9:00 o'clock and at 21:00 o'clock the motor is turned on for 4 seconds. You can change that easily in code.

The code starts counting the time at 12:00 o'clock. So when you plug in the machine at midday or at midnight the feeding times will be set correctly. To have an exact clock even after a power failure you would need an additional real time clock chip (RTC) and a battery. I think this is not neccessary because pets don't care at which time they eat. In the real life in nature the cats will also not eat a mouse every day exactly at 9:00 o'clock. And the Arduino "clock" will only go wrong after a power failure.

Step 12: The First Attempt Which Did NOT Work

It seems self-evident to build a funnel and guide the pellets into the meat grinder.
But this does not work.

Even in a tube of 4 cm diameter the pellets / nuggets will get stuck because they are not smooth and round like peas. My first construction failed because the pellets did not advance.

Step 13: The Second Attempt Which Works

Then I cut off the upper part of the attachment which covers the helix.
Cutting the tube with a saw is easy because it is aluminium. Then I inserted it between two blocks of wood in a plywood construction.

Step 14: Building a Square Box for the Pellets

With MDF of 5 mm I covered the sides. Paint a circle and cut a hole with the form of an "U" with a jigsaw.

Step 15: Building a Square Box for the Pellets

On both sides.

Step 16: Building a Square Box for the Pellets

The box is built around the meat grinder and gets a slide made of a 7,5 cm PVC tube.

Step 17: Insert the Next Floor

The next floor is inserted and two MDF boards act as a funnel.

Step 18: Building a Funnel

For the sides I recommend to cut first a cardboard with scissors and when it has the correct form transfer the pattern on the MDF wood.

The tank easily takes 20 liters of pellets.

Step 19: Ready

The machine stands in my courtyard under a roof.
If you like the design you can use the "Peeking Cat" in the above ZIP file which I painted on the box.

Step 20: Water for the Pets

I have an automatic water irrigation system for my plants. From that I branch off water for the cats.

If you don't have that you can use the same Arduino to control a water valve (which you can take out of an old washing machine) over a second relay and fill a drinking water tank for your pets. With a water sensor you can measure the water level and when required you open the valve. This can be done with a few lines of additional Arduino code.

Another option is to take the same mechanics which is in the water tank of your toilet. This does not require electronics and is very cheap.