Cat feeder improvements (video)

This is just a repost for people who are not subscribed to my youtube channel.

http://benkrasnow.blogspot.com/2009/08/improved-automatic-cat-feeder.html

Improved automatic cat feeder

I recently set up my automatic cat feeder (http://benkrasnow.blogspot.com/2009/02/automatic-cat-feeder.html) for a long-weekend vacation. This was probably the sixth time that I have used the feeder with great results each time. I also setup a motion-activated webcam that posted frame captures to a web server so that I could see the feeder (and cat) while I was away.

One day during the trip, I checked the web server and noticed the feeder had dispensed a huge amount of food. I've never seen my cat eat his fill and walk away from a dish with food in it, but he did this time so there much have been a truly massive amount. When I returned home, I saw what had happened: The cat had knocked over the darkroom enlarger timer, and by strange chance, the timer knob was turned from 3 seconds (an interval that dispenses a single-serving of food) to 20 seconds! The feeder emptied the entire storage chamber of food into the serving dish. It's not possible the cat knew what he was doing by messing with the darkroom timer, but it's also very strange that this happened by mere chance.

I never liked the timer approach to the cat feeder because it assumes the motor turns at a constant speed, and the darkroom timer is not easy to adjust accurately in the range of 2-4 seconds. I thought about adding a shaft encoder to make the system closed-loop. I also thought about using a mechanical means to control the shaft (ie a Geneva Wheel). Finally, I decided to use a strong stepper motor in open-loop control. I also wanted to keep the same gear reduction box that was originally coupled to the food dispenser. It's torque amplification is helpful, and it has also become a structural part of the feeder, so not easy to change.


I removed the old DC motor and pulled the armature off the shaft. I cut the shaft, then built a press-fit delrin coupler to mate the stepper motor shaft to the remaining piece of original shaft (with an integral helical gear on the end). I then made some spacers out of delrin and mounted the motor to the gearbox.


I used an Atmel AT-Mega8 AVR to turn the stepper motor through four shaft rotations when power is applied. I used PN2222 transistors to switch the unipolar motor windings. The transistors are driven through resistors by half the D port in the AVR. The gear reducer's output will spin about 1/6 of a turn, which will advance the "butterfly valve" in the feeder enough to dispense a single serving. I coded the Atmel chip using Atmel's IDE in C with WinAVR. I used PonyProg to download the code into the chip via a simple parllel port interface. I would normally use an Arduino or similar microcontroller for projects like this, but this one is so simple, a full-fledge microcontroller would be overkill and too expensive. The AT-Mega8 is about $6 and needs a $1 crystal. The Arduino is around $30.




My cat stuck his head into a pile of plastic shavings the garage and managed to get a couple scraps stuck in his whiskers.

Automatic cat feeder

See improvements here:
http://benkrasnow.blogspot.com/2009/08/improved-automatic-cat-feeder.html

My cat is a voracious eater, so it is not possible to leave out a weekend's worth of food when I take a short trip away from home. He would eat all of the food in the first few hours, making himself sick! In order to dole out his food in small amounts, I built an automatic feeder out of "found" parts and minimal amounts of machining.

The system starts with a standard "vacation timer" for home lighting. This particular model has a plastic tab for each 15-minute increment of the day. By flipping the tabs in/out from the center, any program can be constructed that has 15-minute resolution.The power cord from the "vacation timer" goes to a photographic enlarger timer. This device allows the AC power to flow through it for a pre-determined number of seconds. I left the "timer" switch in the on position, so the device begins timing as soon as the AC power from the vacation timer is received. This device was indeed homemade, but not by me. I found it at a flea market years ago. The power from the enlarger timer goes to a standard AC wall transformer, and then to a gear-motor on the feeder.

The motor is rated for 24 VDC and originally came from an HP laserjet. I am running it on a 9VDC from the wall transformer, and I also used a ballast resistor to get the motor turning as slowly as possible.

The motor is connected to a dry cereal dispenser (sold for humans!). The dispenser had a knob that could be turned to dispense a quantity of cereal, and I replaced that knob with the motor's shaft. The dispenser's hopper tapers down to a straight-walled cylinder and there is a flexible rubber butterfly valve (of sorts) that fills the cylinder's diameter. The valve has 6 blades, and as it turns, it meters out a specific volume of food. I have the enarlger timer setup to turn the valve 1/6 of a revolution so that the same amount of food is dispensed each time. I also added an output chute to keep the cat's paws away from the butteryfly valve. I also built a sturdy base out of acrylic and wire-tied the whole contraption to a table leg.

This feeder is actually the second version that I have built. The first version was based on a meat grinder (using the auger to meter out food without any blades or grinding plate). It didn't work as well because it had a tendency to mash up the food, or get jammed, and generally not work smoothly and consistently. The new version with the cereal dispenser has worked extremely well.