This is a access control designed to provide access to a manned, but secured location, via either a hardwired button, keypad or keyswitch and or wireless keyfob. It is not designed to and should not be used to provide a method of egress.
A typical application would be a commercial storefront, where a visitor would ring up a buzzer or intercom and once identified someone inside the secured location would "buzz" the door open and allow them to enter.
Now the most common problem with door buzzers is, someone has to press a button and hold it until the person at the door gains access, this often leads to a series of errors in timing and sometimes a bit of frustration.
This design solves that problem.
Over the years I have built a few dozen of these but never documented such, the reason being, until this forum came along, who would care?
None the less here we go.
The bill of materials is:
A power supply and transformer that matches the door strike.
A wireless receiver that will provide a positive pulse when it receives a signal from a learned transmitter.
A timer module, I use the Altronix 6062.
A sensitive relay, again an Altronix RBSNTTL.
A 100mf 50 volt electrolytic capacitor.
A Gel-cell battery or batteries to match the power supplies voltage.
A housing for everything to be installed into and battery terminals, hookup wire, Ty-Pads and Ty-Wraps.
The operation of this control is very simple, once an access button is pressed and access is then granted via a contact closure, the timer unlocks the door strike and holds it unlocked until it times out, this allows the laggard at the door plenty of time to get their act together and enter the building, but we don't want that door strike to remain engaged once the person opens that door, enters the building and that door closes latching into the strike.
Follow throughs are a serious security risk.
This is where the sensitive relay comes into place, the power for the timer and the strike are provided through the normally open contacts of the sensitive relay, in turn the sensitive relay is energized by a standard normally closed alarm system magnetic contact installed on the door, as long as the door is closed the sensitive relay remains engaged and provides power to the timer and the strike it controls.
Now, once the door is opened, the magnetic alarm contact drops out causing the sensitive relay to drop out and dump power to the timer and strike, ensuring once the door closes, it will be secured by the strike.
And as for the 100mf cap, it gets placed between the + and - terminals of the sensitive relay, it's propose is to provide a couple of seconds delay in the drop-out of the relay to suppress any inductive kick-back from the strike falseing an door open condition on long cable runs, where it is common for the strike and door position contact to be within the same cable.
http://www.matrixblackrock.com/Assets/ac2.jpghttp://www.matrixblackrock.com/Assets/ac1.jpghttp://www.matrixblackrock.com/Assets/ac1.jpgWayne
Anyhow I added a couple of 47 ohm 5 watt resistors in parallel that are then wired in series with the strike feed, this dropped the voltage to the strike to 14 VDC under load, a second addition based on a recommendation by tomasfuk, was the inclusion of a 100 ohm 1/8 watt resistor to limit the current on the door closed loop, preventing the snubber cap charge amperage from damaging the reed switch in the door closed contact and a third addition was the addition of a green LED pilot light to visually indicate the unit had received a valid code and was powering the latch. 
