I have two dogs (a miniature schnauzer and a westie) that eat different types of food. But they like to eat each other's food and not their own. So, I've looked for a cheap method to regulate their habits and this is what I've came up with.
The more of these you need to build, the cheaper it gets. For example: 1 RFID reader is $10 but 4 RFID readers are only $22. 100ft of copper magnet wire is $6 but 900ft is $18 (I used about 100ft per antenna).
You could get down to $17.25 (5.5 for the RFID reader + 2 for the copper magnet wire + 0.5 for the battery connector + 3 for the 9V battery + 1 for the plastic bowl + 5.25 for the alarm sound buzzer)
All the details are in the *.PDF file
The video contains the first iteration of the system.
The only changes are:
* everything was glued in place instead of drilling holes and zip tying everything
* the RFID module was modified to have a smaller footprint and placed at the bottom of the bowl (instead of the side of it)
* used a 9V battery instead of 12V DC from a wall transformer
* switched from the huge alarm to the smaller one
Let me know if something isn't clear.