All that's needed is a Webcam, Flashlight, Free Software, and about $15 worth of analog electronics that you can get from radio shack.
This system allows remote control (via the internet) of actuators (motors, etc) at your home. It works by sensing changes in brightness at particular locations on your home computer screen (locations at which the sensors are taped). These changes in brightness are remotely controlled by you via a yahoo messenger webcam video feed between your work computer and your home computer.
For example: you're at work with a computer, a webcam, and yahoo messenger's video broadcasting activated. Your home computer is also running yahoo messenger and has a full screen view of your work computer's webcam video feed. At work you shine a flashlight into your webcam's field of view at specific locations. By varying where you shine the flashlight into your work computer's webcam you will be activating different sensors/motors at your home computer.
If this is confusing make sure to watch the video.
Advantages of this system over much more complicated systems:
= Optical isolation of PC from actuators (motors, etc)
= Uses only cheap analog components available from radioshack
= Allows control of as many actuators as desired.
= Does not require knowledge of computer programming, or server administration (i.e. PHP and Apache)
= More secure than remote desktop access software such as VNC, etc because yahoo messenger does not allow access to control your entire computer. (as far as I know,.....this last advantage might not be totally true :)
Step 1: Supplies
soldering iron $8
wire wrapping tool $7
(you can wire wrap directly onto component leads instead of soldering. it's less permanent but ok for prototyping)
30 gauge wire wrap wire: $4
needed as a flexible wire between screen mounted photoresistors and the breadboard.
photoresistor 5 pack: $3
2n222 transistors or relays $3
DC power supply (you probably have this): $20
you can find these in the garbage, or you probably have spare ones from appliances you don't use any more. the voltage output you need depends on the size of the motors you use. many medium sized motors need between 9 and 12 volts.
breadboard for testing $8
Step 2: Setup I
(1) Install yahoo messenger on your work and home computer: http://messenger.yahoo.com/
(2) Connect a webcam to your work computer. Set it up so it's looking at a dark, flat surface. I used an existing PVC frame I made for the camera. (first image)
(3) solder or wire wrap a long length of 30 gauge wire wrap wire to each of the photoresistor leads.
(4) Tape photoresistors to your home computer's screen. I did this by first taping the photoresistors to a clear piece of plastic with black electrical tape, then taping the plastic to the screen with scotch tape. (second image)
(5) I would recommend putting the 'home computer' in a box to exclude any non-screen light. otherwise light from windows could interfere during the day. You will be maximizing the yahoo messenger video feed on this home computer so that it fills the whole screen (or as much of the screen as needed to be able to activate all of your taped on sensors).
Step 3: Setup II
(1) set up the circuit on a breadboard according to the diagram (first image). You can test out the photoresistor by covering it with your hand (second image).
(2) make sure to have all of the power supplies for your circuit plugged into a surge protector (i.e. a power strip with a circuit breaker)
You'll have to change your screen brightness setting to one that works best. i.e. the brightness at which the photoresistors won't conduct electricity when the screen is black, but will conduct enough electricity when the screen is white to activate its transistor/relay. I found that with some photoresistors I had to put a piece of paper between them and the screen to help modify the brightness getting to it (see previous note).
Step 4: Setup III
(1) make two accounts for yahoo messenger (need two email addresses, get free ones from hotmail or gmail or something). Make one account name end in "....work" and the other account name end in ".....home" so easy to remember which will be used on which computer.
(2) make sure you've added your "...work" account as a friend on your home computer
(3) make sure you've added your "...home" account as a friend on your work computer
(4) Edit the settings on yahoo messenger on both computers to allow anyone to view your webcam without permission. (image 1)
(5) Edit settings to start "Super Webcam Mode Automatically". (image 2)
(6) On your work computer start a yahoo messenger webcam video feed and leave it running. (image 3)
(7) On your home computer click to view your work video feed. Change the size so it fills your home computer's screen (or make it as large as possible to be able to activate all of the photoresistors taped to the screen). (image 4)
(8) At work shine a flashlight into the camera's field of view at different locations to activate different sensors on your home computer.
It would be best to have a webcam on your home computer too so you could watch that everything is working properly from your work computer.
Step 5: Helpful Notes and Conclusion
(1) It's best to have a webcam plugged into your home computer as well so that you can watch what's happening via yahoo messenger at work. That way you cam be sure everything's working smoothly. I didn't have a second webcam so didn't show that.
(2) Make sure to test your system like I did for a full day before putting it to use while you're away. Because it is not a digitally implemented system there are little ways in which the 'real world' will interfere with it. For instance the photoresistors might fall of the screen, the changing of the light through windows during the day could have an effect on the photoresisors if they aren't properly sheilded.
(3) If you want to control something wirelessly with this system I would suggest using something like this:
just replace the switches shown in the schematic with transistors controlled by photoresistors. Take note that the range isn't that great for the Tiny-IR-II transmitter. Also, it uses IR infrared (like a tv remote), not RF (radio).
(4) Might be good to make one photoresistor a "Circuit Activator". In other words connect it to a relay or transistor that controls the power supply to the circuit. In this way you have a 'kill switch' that can shut the whole thing down if it starts acting wacky.
I hope that this helps people and helps make some pets happier when they're at home alone. The beauty of it is that it's so easy to set up that you can do it in a couple minutes, and it requires no special skills and barely any money.