Hello Guys!
Here is a break down of what I'm trying to do....
I have a Door King keypad on a front gate and it works great. It used a 16 VAC power supply that powers the Door King panel as well as an electric door strike; when the correct code is entered, 16VAC is sent to the door strike for about 3 seconds which allows the door to be pulled opened.

Secondly, I have a spare Schlage NDE lock that I plan on utilizing for this project. The lock is powered by 6VDC. When a key fob is presented to the lock sensor, it sends a signal to a tiny electric motor that spins and engages the door lever mechanism. After about 3 seconds is reverses polarization and disengages the door lever mechanism. The voltage of the signal sent to the motor is small and brief. My multi-meter picks up about 250mv DC for about a 1/4 second. I suspect the voltage might be higher, but due to the short duration, my multi-meter doesn't pick it up. On a side note, if I connect the motor to a AA battery, it does turn robustly. Hence, when a key fob is read at the Schlage lock, it sends a signal to the motor which spins and engages the mechanism; after about 3 seconds it sends a reverse polarity signal and the motor spins the other direction to disengage the lever.

What I am trying to do is incorporate the fob reading ability of Schlage lock to temporarily activate the electric door strike. On a side note, they do sell the system to handle this, however, its about $1200 - so I figured that I'd try to Frankenstein my own system since I have a spare lock.

What I was thinking was to have the output from the Schlage lock sent to a relay between the 16VAC power supply and electric door strike (I feel like some diodes would be necessary here, but I haven't figured out where they go!). However, there were 2 problems I ran into immediately;
1) the output voltage of the Schlage lock is very low (about 250mv), and apparently relays need more voltage to work.
2) a normal relay wouldn't really work because it only activates with continued power. The current system powers for a brief moment, then reverses to undo the connection. I searched around, and it seems that there is a relay of this sort - maybe called a latch relay or single coil relay. But it looks like these wont work regardless because of the first issue regarding the low voltage.

So ultimately, the question incorporating the two systems is -
What can I use that would do the following
1) receive a low voltage signal (maybe 250mv) and trigger a 16VAC connection (to the door latch)
2) receive the reverse low voltage signal and undo the 16VAC connection.

Lastly, the electric door strike has 2 wires that connect in a loop between the 16VAC transformer and control panel. It is also connected to the Normal Open setting in the panel. If I figure out the Frankenstein key fob mechanism, and I were to wire it in between the transformer and electric door strike, would I have to put in some diodes to prevent the electric from going to the panel? Or would that be a moot point if its on the NO circuit.

Lastly, if anyone wants to see pics or anything to help explain this, let me know.
Thanks guys!

 

Since the output from the key fob receiver is so low, it makes sense to use comparators to interface with higher voltages. The LM339 comparator family ICs have four open collector comparators and can operate on 12 volts. you can put two comparators in parallel to sense each output polarity and have a solid open collector pull down for each function, lock and unlock, and still have the use of the original small motor.

 

Welcome to AAC.

The first step is to get an isolated signal from the Schlage that can be used to trigger the strike. The obvious way to do this is with an optoisolator which is basically an LED and a phototransistor in a single package.

When the LED lights, the phototransistor turns on. This provides galvanic isolation—that is, there are not electrical conductors connecting the two systems.

The input to the opto is easy to drive so it shouldn't be a problem for the lock. The output can easily buffered with a transistor and attached to a relay giving you a simple switch to work with.

 

A comparator , or a MOSFET transistor, will be the most sensitive device to detect that the small motor is being driven.