Pet Feeder with RFID

Hi there,
I’m new to Arduino and I want to build a pet feeder. My first attempt with coding was simply turn on a pin to activate a relay connected to a motor for a cretin length of time, using a delay, then with another 12 hour delay repeat the process. Like I said in the subject line i would like to add RFID to my project to only allow my pets access to the food and keep the possums out. I don’t think my first approach to the code will allow me to add the additional functionality. So i was hoping someone could steer me in the right direction in regards to coding this right. I don’t know is there some way to program a timer?

So i was hoping someone could steer me in the right direction in regards to coding this right.

First, make sure that the hardware can do what you expect. RFID readers do not have much range. How will your pets be tagged? Will they be able to (and smart enough to and inclined to) get the tag close enough to the reader?

Second, start with a clear statement of requirements. Under what circumstances should the Arduino activate the food dispenser? Every time your pet approaches? Only once or twice per day when the pet approaches? How much food should it output? How will you measure that? Is time sufficient?

I don't know is there some way to program a timer?

There are. But, you don't need to. The Blink Without Delay uses a timer, but there is no programming of that timer required. You don't need to program your watch, do you?

Maybe this will help with your timer question (from Arduino Playground):

I used this to create a "Meal Time" device for our dog because she has a way of convincing you that she's hungry even though someone else in the house just fed her 10 minutes ago, (or everyone assumes that someone else gave her breakfast, and her meal might get skipped). It's a box with a red LED for "hungry" and a green LED for "happy" and a de-bounced button to push when you feed her. I set the delay for 8 hours. When you feed the dog you push the button and it lights up green "Happy" until the timer runs out, then it lights red "Hungry". Now everyone knows if she needs feeding or not. We've been using it for months.

You have not said what kind of pets you have, or how smart they are.

Looking at the posts by PaulS and DRBArduino made me think about a couple of things.
You probably don't want to feed the pets every time they want fed.
However the animal needs to learn how to operate the feeder and that could be tricky if sometimes the animal gets fed and sometimes it does not.

For the animal to learn to use the feeder I think the feeder needs to indicate that it is "willing" to dispense food.
So when the feeder is prepared to dispense food it needs to have an LED, flag, sound or something, that tells the animal I will feed you if you wish. When the animal sees the indication it can then do whatever is required to trigger the food release.

hi there,
thanks for all your responses. I should be more clear I've figured out the timed dispensing part now what i need help with is allowing access. The dog has a taste for the cat food and now he's a big fatty so i want to restrict his access. I have a adafruit PN532 stacked on an Uno and i can attach RFID tags to the cats collars so when they approach a servo will open a door.