Simple and Reliable Cat Feeder With Block Programming

Our beloved cat Gloria has an eating disorder - she will eat every bit of food in the tray no matter the amount. Sometimes the food even decides to return from the stomach, so we either have to make a vomit cleaner or a pet feeder! Having a pet feeder is also great if you travel a day or two, as the feeder can store food for up to 4 days.

This build includes all drawings and measures as well as a downloadable hex file for the microcontroller. The function is simple yet reliable. No clogging or jamming ever! I have developed and optimised this machine for more than two years and the design has become very sturdy.

This feeder can be made with common tools, with a scroll saw as the most advanced part. All mechanical parts are made of wood, and the feed control is taken care of with the BBC micro:bit, which is a very easy to use device, even for people who never used a micro controller before.

And just in case - there is a 3mf file for 3d print users - you are welcome!

Food container

Approx. 0,6 liter round food container, plastic

The container should have a slight cone shape, (wider near the opening), so the food will have a small slope to run down when spinning.

Sticky velcro tape (optional)

Main construction

36x48mm/ 1,5x2" construction wood

Some 4mm and 7mm plywood

Thin, flexible plastic sheet such as dining table plastic sheet (polypropylene)

4x m3 screw, 6mm or longer (can be m4)

4x m3 nuts (can be m4)

2x wood screws about 20mm long

4x wood screws about 40mm long

10x75mm round wood pin or aluminium pipe

Electronics

BBC micro:bit V1 or V2

Multi:bit control board with gear motor or other relay/motor controller board for micro:bit

Discarded USB cable

USB power supply/mains plug converter

Tools

Drill

3mm, 4mm and 10mm burrs (the latter must have the same diameter as the wooden pin)

Stepping burr, up to 2 times the diameter of the food pellets

Scroll saw, dremel cutter or fine wood saw

Combination square or other measuring tools

Disc or belt sander (optional)

Compass (optional)

Printer (for gearwheel layout)

A few clamps

Soldering iron

Wood glue

Epoxy glue

Food

I have only tested round pellets and they work great! (For the cat, not the maker)

Download and print the drawings for detailed instructions. You can even glue them to the plywood sheets for easy cutting with the scroll saw. The parts in the left are 4mm, the rest is 7mm. It can be thicker, but the wood pin would have to be slightly longer to reach through the gearwheel and the box holder discs (right).

The round discs can be made with scroll saw or hole saw, the latter is faster. After cutting and burring you can mount the disc to a bolt and spin it - to make a perfect smooth edge. This method is also perfect for the wood pin, to make the edge smooth and round. This greatly helps installing the discs and gearwheel.

Rounded corners are optional but looks great.

I prefer to start with a combination square. Set it to the radius of the quarter-circle to mark the center in both directions.

Use a compass to draw the curve.

Cut roughly outside the marking. Don't cut the marking!

Finish off with a disc sander. Rotate evenly until you have touched the markings evenly.

Cut the micro:bit holder just like the other plywood parts, using 4mm plywood, scroll saw and 3mm burr.

Can we make gear wheels without complicated tools? Yes of course! Making gear wheels is a great skill builder and not as hard as it sounds.

Start by printing the pdf in 100%

Cut the drawings and glue them to the plywood. I recommend wood glue or paper glue.

Punch holes around the inner part of the teeth for more precise burring and drill with a 4mm burr.

Then, with a scroll saw, cut all the straight lines to remove the "cavities". The most important thing is to keep the teeth smooth without jagged edges. They do not need to be perfect in width but make sure they don't go outside the outer circle.

Sand or grind the teeth a little so they are smooth

Drill a center hole, 5,5mm for the small wheel and 10mm for the large wheel. Keep it tight, then the wood pin can be press fitted and mounted without glue.

The splash sheets will prevent the cat pellets from being tossed all over the place.

Mark the sheets with a ruler. The size is about 60x120mm. One side can be longer (150mm) because there will be more food spill on one side depending on the rotational direction. Cut them slightly bigger than you need, then you can trim them later after testing.

The simple design provides an even, clog free dispenser function. The holes are bigger than the pellets, but because they clog up, the pellets will only run through when spinning!

The key is to have the right hole size around the container. I found that approx. double the diameter of the pellets will work the best.

Drill four holes, near the opening (90 degrees = evenly around the box opening)

Be careful not to break the plastic! I found that stepper bits works best. If using burrs, start with 3mm and work your way up. Some cheap boxes can crack easily. Use higher quality polypropylene boxes like Tupperware or similar.

If you want, you can stick the box to the ring with some velcro. First glue the velcro on, cut around the disc. This will let you remove the container for refill etc. But you can also just glue it directly to the 60mm disc.

Start by gluing the food slide together. Clamp them to the 36x48 wood block for support. You can mount the sides first and adjust them before you add the glue.

Meanwhile you can screw the base plate and the micro:bit holder to the main block. Use the pdf for reference on all the screw holes and distances.

Drill holes and attach the splash sheets with four m3 screws and nuts.

Use the last image for reference on how the full assembly looks.

Simply lay the feeder on its back and remove the box lid, then fill it

Don't pack it, the pellets must be able to turn. Leave a little air.

Please note that someone might try to snatch a few coins while you do it!

Cut the old USB cable near the small end. De-isolate and locate the red and black cable. At the backside of the multi:bit control board, Solder the red to + and black to the - pad.

Install the nylon screws and aluminium spacers that came with the control board. Mount the micro:bit on top.

Finally, add two nuts behind the plywood micro:bit holder to secure the boards and connect the motor on the left side.

Connect a micro USB cable between your computer and the micro:bit. A micro:bit USB drive should appear on your file browser.

Download the hex file to the micro:bit. Depending on the version, you might get an error message (020) and a sad face.

If so, head over to makecode.microbit.org, and import the file there. Connect the micro:bit and it will adjust the code to match your micro:bit. More about transferring here.

Makecode is also the tool you need for adjusting the code. The great thing is that it is so simple and all you need is a web browser!

When the proper code is running, a clock will scroll across the screen, starting with 19:00.

Glue the small gear wheel to the gearbox motor using super glue or epoxy.

Make sure the micro:bit is running the new code. A clock should scroll across the screen (not a sad face!)

Test the spinning by powering on the USB and pressing button A on the micro:bit (left side).

Test the gear wheels by clamping the motor to the wood pole. Experiment with a proper distance between the gear wheels. Test that the rotation runs smoothly and remove any jagged teeth if there is any hiccups. Some oil or silicone spray can help too!

When you have found the placement, sand the motor and the wood part before gluing them with epoxy. For a long, reliable machine, epoxy is the way to go! I have tried super sticky tape and super glue, but they will only last a few months!

When the glued have cured, connect the USB power again and get ready for some final adjustments!

The code I have written, contains a clock and 9 meals pr. day. It starts the feeding every second hour starting 6:00 and continuing until midnight. We skipped 12.00 feeding because Gloria often sleeps at that time.

Clock adjustment

The clock starts by 19:00/7 pm by default. It can be changed by pressing button B. The clock is not meant to be very accurate, but just so the feeding doesn't run at night. The clock will have some drifting each day and after a few months of operation, you might need to reset the micro:bit because the clock register has run out, resulting in negative time!

Feed schedule adjustment

See the second image. The feeding times can be edited by adding more instances of the "if hours = xx". Delete or copy a instance, and make sure the hours is set properly to the time you want.

Feeding amount adjustment

The key to regulate the amount of food at every meal is the feeding time, or how long the drum spins. It's currently being calculated to 6 seconds. To find out how much food it gives, do the following:

• Fill the container about 2/3rds up.
• Press button A the same amount of times the feeding is due one day (9) but wait for each feeding to finish before pressing the next time.
• Weigh the food that came out and make sure it is what you want for your cat.

You might notice that after a while, the cat will go crazy just of the sound of the machine. Expect your cute friend to wait for hours then jump 10 feet in the air just of joy from that tumbling sound!

If you want to take it further, the micro:bit has sensors and radio control. A few ideas that you might want to play with:

• Remote controlled feeding (using the built in radio)
• Automatic daytime feed based on light sensor
• There is even a tilt sensor - that can be used to alarm you if the little bastard tries to break into the bank! (And yes, the micro:bit V2 has a speaker for that too!

I hope this tutorial was helpful! It was really fun but also a lot of work. Please consider supporting me by checking out our website or following my Instagram.

Comments and thoughts are welcome. I will try to answer any questions!

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