1) Has a second secret input for when people are around who could overhear your knock. Now a photo-diode can register a "photo knock" (light flash) through the peep hole!
2) Includes an H-Bridge, giving it the ability to both Unlock and Lock a door (changes the direction of voltage across motor)
3) Programing now records the average (background) noise/sound levels and adjusts the sensitivity (threshold values) accordingly
***The information here is adapted from Grathio's instructable. Many thanks and credit go to Grathio Labs for making such a comprehensive guide available to the rest of us! I will take you through the steps for programming and wiring the electronics and then send you to the step in Grathio's instructable for making a PVC door mount (sadly, I am still in the process of creating a functional case)
For Grathio's original Knock-Lock instructable, go to http://www.instructables.com/id/Secret-Knock-Detecting-Door-Lock/
Step 1: Tools, Supplies, and Skills
To complete this project you should be able to:
Do basic soldering.
Read a schematic.
Have some knowledge of microcontrollers (I'll be using the Arduino.)
Drill (ideally a drill press) and an assortment of drill bits.
Saw capable of cutting PVC pipe. (ie: Pretty mcuh any saw.)
Soldering iron and solder.
Heat-shrink tubing and/or electrical tape.
Other things you might find handy: a ruler/tape measure, a multimeter, a breadboard, some tape, a magic marker, sand paper, files, hot glue. And if you're like me a well stocked first aid kit.
1 Arduino Uno (or similar) Microcontroller
1 12v Gear reduction motor with high torque
1 Small Microphone
1 SPST momentary pushbutton. (normally "off" / "open")
1 Red LED
1 Green LED
1 Quadruple half H-Bridge SN754410NE chip
1 100k ohm resistor (1/4 watt)
1 10k ohm resistor (1/4 watt)
1 1M ohm resistor (1/4 watt)
2 560 ohm resistor (Or whatever will run your red and green LED's at 5v)
1 small piece of perf board. 5x15 holes or longer.
1 12V Wall Adapter plug for Arduino
It's also a good idea to have a breadboard for setting up and testing the circuit before you solder it. We'll be doing this in step 3.
(This design comes directly from Grathio source.)
20" PVC Pipe 1/2".
3 right angle 1/2" PVC connectors.
1 5-way 1/2" PVC connector. (example)
2 1/2" PVC end plug.
3 1 1/2" suction cups. (Available at hardware stores and craft centers.) NOTE: If your door is unsuitable for suction cups then replace these with three end caps and you can use adhesive strips or screws to mount the lock.
6" of 1/2" wide by 1/64" thick metal strip (steel, tin, copper, etc.) (available at hardware, craft, and art supply stores.)
4.5" of 1" wide metal sheet, 1/32" thick (steel, tin, copper, etc.) (available at hardware, craft, and art supply stores.)
2 3/32" x 3/8" screws with nuts. (1/8" will work too if you can't find the smaller ones.)
2 1.6M (metric) 16mm screws. Ideally with countersunk heads if you can find them. (For securing the motor. Check your motor specs to see what screws it needs. One motor I tried used 1.6M, the other 2M. You'll probably have to buy long ones and cut them to length.)
1 Large Suction Cup (for photodiode)