This is a fun an very useful project that allows easy access into any door with a deadbolt. I have another version that is used on my garage door and uses the same basic circuit and fobs. The system operates in the RF region at 125 KHz. Fobs are used to actuate one of two relays on the main control board. With each scan the deadbolt toggles - if it is unlocked it locks and the red LED comes on, if locked it unlocks and the green LED comes on. One relay causes the deadbolt motor / mechanism to lock the door, the other causes the door to unlock. A regular key can still be used and the deadbolt can still be locked and unlocked manually if desired. Operating the circuit with the key or manually operating it with the deadbolt knob can cause it to fall out of sync with the controller and indicate locked when it is actually unlocked or vice versa. To correct this just cycle the unit with the pushbutton on the deadbolt housing or flip the deadbolt knob the opposite way. I have thought about adding some limit switches to eliminate this problem. Perhaps in some future version I will implement them. I have been using this project for a couple of months with very few hiccups. It is fun to build and adds a definite 'nerdivity' to my home.
I based the project on a store-bought electronic deadbolt. It was battery operated and had a keypad on the outside to allow entry with a user defined code. I removed all of the electronics from the indoor housing keeping only the electric motor and mechanism. The mechanism has a built-in clutch that prevents damage should the motor remain on for too long when cycling. My motor is set for a cycle time of about 1.25 seconds.
This project is based on the Kwikset Powerbolt Model # 907 15 SMT CP. It cost $69.97 at Home Depot. Almost any battery operated deadbolt will work. It needs some type of clutch mechanism to protect from over-cycling. This was the cheapest unit that Home Depot sold. You may get lucky and find an open box item or a defective unit that can be salvaged. It looks neater than trying to build the motor drive myself.
In future versions I will try to place all components inside the plastic housing where the OEM circuit board was located. There many similar projects you can research on the internet. Do a search for 'RFID ARDUINO DEADBOLT'. There a few on Instructables as well. A Universal RFID Key by drj113 available in Instructables is a good read on RFID theory. Going over this material will be time well spent.