Keyless Dorm Entry

Step 7 Software

The last part of it all is creating the software that ties it all together. Unfortunately, the SX has a very limited amount of memory to work with so it required a few tricks to make the software work.

There is a flow chart of the design.

Some important things to keep in mind: Because of the limited memory of the SX48, it's not a good idea to attempt to store the entire data of the card or the entered key. The simple solution to this is to have a byte that remembers what 'place' it's on in the key or card. When a mistake is made, that is remembered, and the place variable is increased. That way, it only needs to remember if there was ever a mistake, and if there wasn't, and the end of the key/card is reached, the data must be OK. For security reason, it's very important that the system keep letting you scan a card or type a key once it determines a mistake has been made. Otherwise, it would be easy to break such a system by trying different keys. With all of these design considerations in mind, the system will remain completely secure while at the same time not need to worry about the limits of the hardware.