This started out as a bit of a joke project, but turned out to be surprisingly accurate at judging knocks. If the precision is turned all the way up it can even detect people apart, even if they give the same knock! (Though this does trigger a lot of false negatives, which is no fun if you're in a hurry.)
It's also programmable. Press the programming button and knock a new knock and it will now only open with your new knock. By default the knock is "Shave and a Haircut" but you can program it with anything, up to 20 knocks long. Use your favorite song, Morse code, whatever.
Maybe a video will explain it better:
(I hate to even have to say this, but since someone's going to say it, I'll say it first:)
1) This is for entertainment purposes only. Really. This decreases the security of your door by adding another way to unlock it, and it makes your unlock code known to anyone who can hear. If you put this on your door, be sure to carry your key too. The batteries might die, the suction cups might fail or you might forget your knock. Don't complain to me if someone imitates your knock and steals all your stuff, you've been warned.
For obvious improvements to safety, security and whatever, see the final page of the Instructable.
2) This is not a project for a beginner! Read through it carefully and be sure you understand it before you start! I will not take time to answer questions that are already in the instructions or from people who have gotten in over their head.
(If you think this project is too complex you might go here and sign up for the kit mailing list. The kits will be much more simple than this.)
Sorry about that. Now that that's out of the way, lets get to work.
Step 1: Tools, Supplies, And Skills
(If this all looks too challenging, you might consider signing up to the kit mailing list which, when available, will be much easier and a lot more simple.)
This project will take several hours to complete.
Skills:To complete this project you should be able to do the following:
These are important! If you're not sure if you have these skills, read through the entire Instructable and make sure you understand it before starting anything!
- Basic soldering.
- Read a basic schematic.
- Basic knowledge of microcontrollers (I'll be using the Arduino.) This means you know what one is, how to upload data to it, and how to make minor changes to code.
- Improvisation. There are many ways to do this project, and you will have to make changes based on how your door and lock works.
- 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.
- Screw drivers.
- Heat-shrink tubing and/or electrical tape.
- Wire stripper.
- Safety glasses.
Materials:(The links are for example only, I don't necessarily recommend or have experience with any of these vendors. Feel free to suggest other sources in the comments.)
- 1 Arduino Duemilanove (Or compatible. Or really any microcontroller with at least 1 analog input and 3 digital outputs.) Buy from here, here, or here. And other places.
- 1 5v Gear reduction motor. The higher torque the better. Here's a good one. (14-16mm diameter is ideal because it fits inside of 1/2" PVC pipe.) I recommend one with at least 15oz/in (11 N-cm) of torque at 5v to turn a basic lock. 1
- 1 Piezo speaker. (30mm) similar to this. You can use larger or smaller ones, smaller will be less sensitive.
- 1 SPST momentary pushbutton. (normally "off")
- 1 Red LED
- 1 Green LED
- 1 NPN Transistor P2N2222A like these or these (or similar).
- 1 Rectifier Diode (1N4001 or similar) this or this will do.
- 1 2.2k 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. How to tell.)
- 1 small piece of perf board. 5x15 holes or longer. (example)
- 1 9 volt battery clip and 9v battery. (Or any other way you can think of to get 7-12v to the Arduino. A wall adapter like this is a great option so you don't have to worry about batteries running out. 6 AA's would be another option for longer lasting power, but it will bring down the suction cups.)
- Connector wire. 20 gauge or narrower flexible wire in a number of colors for connecting the electronics together.
Case:(These items are to make the project as pictured. Feel free to build a completely different and more functional case.)
- 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.)