While looking around the aquarium section of one of those big pet supply stores, I came upon a display of female Bettas (Siamese Fighting Fish). Long story short – after plunking down $4, I have a new occupant on my desk:
The Betta food I use are the little pellets you see on the right side of the picture. This little fish lives on almost nothing – 2 or 3 pellets a day. I’ve had pet fish in the past and when I used to travel a lot it was always a problem figuring out a way to feed them while I was away. So as a day project I decided to make an auto feeder.
I’ve been experimenting with micro controllers a lot lately so the first thing that came to mind was a micro controlled servo that kicks out pellets once or twice a day. Then it struck me that the basic requirements for my device could be met with a cheap clock movement. The type of clock movements I am referring to are in the $1 clocks you see at thrift stores that run on a single AA battery. The clock movment can provide a regular periodic motion (2 revolutions per day on the hour hand), have a fair amount of torque (better than 3600:1 gear reduction on the hour hand), – and they only cost a buck ($1).
To feed the pellets I made a little screw driven hopper assembly. The screw feed itself was made from a stainless steel wood screw. The thread size on the screw is just wide enough to hold the pellets. Each thread pitch would represent one 12 hour feed cycle – 2 pellets a day.
I used a lathe to turn down one end of the wood screw so that I could slip a tight fitting piece of vinyl hose over the end as a coupling. The vinyl hose was just the right size to also have a tight fit over the shaft of the hour hand on the clock.
For the hopper body I cut a piece of UHMW polyethylene . The UHMW PE cuts really easy and has a slippery surface so the rotating screw is less likely to bind. The slippery surface on the UHMW PE should also help with the food moving along its length.
The only problem with using the UHMW material is that adhesives don’t hold to it very well. To mount the hopper to the clock body I had to make another piece that I could stick to the face of the clock and provide a set of threads that I could use to fasten the hopper to. To make this stick-on mounting plate I used a piece of Acrylic with two 6-32 threaded holes. On the back surface of the acrylic plate I used a piece of 3M adhesive tape.
Here’ what the final assembly looks like:
The slot on the bottom part of the hopper assembly allows the feeder to hang on the edge of my small fish tank. Here’s a close up of the feed screw with some pellets in it – should hold enough food for a week.