This page is a "leaf" on a tree with information about remote sensing. It is a leaf of the branch about putting an IP camera (a bit like a webcam, or CCTV) on your LAN, either for local viewing, or, if you want to "open the doors", viewing from afar across the internet.
If you are just getting started with using IP cams, you may want to visit an overview of using IP cams I have provided.
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My basic FarWatch system only requires a PC which you are willing to leave running and an internet connection. For about $40 you can add hardware to monitor temperature at the premises. That is just a start. With FarWatch, you can monitor many, many things. And my ArduServer lets you do similar things for even less, if you can "drive" an http://www.arunet.co.uk/tkboyd/ele1psa.htm.
But! Back to the point of this page: Information about using the digital I/O capabilities of some IP cameras. See the grandparent of this page for more general points on using IP cams.
Exec summary of one detail: All digital inputs of which I am aware involve two terminals (places to connect wires) on the outside of the device offering the input. Some digital inputs ONLY want a switch (or electronic equivalent) between them: The path between the terminals should be (nearly) 0 ohms, or many meg-ohms. These are the simple ones.
Other digital inputs, "see" the "input" when one of the terminals is connected to a voltage. The other terminal would be connected to the ground of that voltage. Obviously, the size of the voltage matters. Usually, "which way around" you connect it matters too. With these, sometimes leaving the terminal that gets the voltage unconnected when not connected to "the voltage" will be okay. With others, it should be connected to ground ("voltage=0") when not connected to the higher voltage.
Happily, if what you want to feed (switch closure or voltage change), and what the camera "needs", in order to respond, can be "matched up" with simple external circuits, if they don't already match in your circumstances. And a transistor can be used as a "switch". A digital output from some other source would most neatly "fit" a device wanting a voltage on the input... but even if all is well to that extent, the level of the voltage provided by the output may be an issue. The amount of current that the input will sink will rarely be a problem.
So many permutations! End of "exec summary".
Most IP Cams come with amazing capabilities to do things with what they see. They can save pictures or video clips, send those images or clips as attachments to emails, send them to FTP servers. Etc, etc.
But it is still a case of "catch your rabbit". How does the camera know when to save or send an image? The simplest cameras will do so on demand, or according to a schedule. (Great for recording time lapse sequences!) Many will detect motion... well, a change in the scene, and save or send then.
A few... at least a few in the sub- $200 world!... can also accept external triggers. You wire up some "stuff" which "boils down" to a switch, and when the camera sees the switch's state change, it does what it has been set up to do... send a picture, save a video clip, etc. This is control by digital input. We'll come back to this.
Some cameras also have digital outputs. Such cameras can, in addition to the usual tricks of saving or sending clips or images, also turn external things on or off. The most obvious example is an alarm bell. Camera "sees" movement? It turns on the alarm bell. (If you think this would be neat, set it up with a quiet buzzer, at first. Motion detection is very tricky in all but the simplest circumstances. You will want to debug your setup before inflicting multiple false alarms on the neighborhood!). See below for more on digital outputs.
For a long time, web cams and IP cams have come with software to do all sorts of Good Stuff with the image they are "seeing".
But it never quite does what I want. Wouldn't it be cool to be able tell the camera "take a picture" by something external. It could start with a simple "doorbell" type switch, and be improved and improved until you had exactly what you wanted. (An Arduino might be involved! Wonderful hobbyist friendly microprocessor.)
Well, a few IP cams have what you need: digital inputs.
In the simplest applications, you just wire a switch to the input. This could be a "doorbell" type switch, which closes when you press it, and you would be able to, by pressing button, say "take picture now". (Yes... that could, really, be a useful setup. Email me if you really need to be convinced.
In another simple application, you might have a long "wire" running around a protected entity... remember the silver tape you used to see stuck to windows? Break the window, break the tape, set off the alarm. In such an application, the contacts of the digital input would normally be closed, and openiong them would trigger the "take picture (or video), save (or send) it."
(It is easy... and I think always done... to provide the IP cam with a setting which lets you choose whether opening the external input, or closing it, triggers the actions you have said should arise in the event of triggering.)
After that, things get a little more tricky, and you need to learn a little bit about digital electronics.
Sometimes you can use an output from your circuit to feed directly into the input of the IP cam. (You must, in these cases, also connect a wire to bring them both to a common "goruond", or "0v".... this isn't "something special"; it's just something "everyone" (who does these things) "knows".)
If you are a digital electronics beginner, you can give your IP cam a little protection, and deal with things like level shifting, etc, which may be necessary anyway, by putting an opto-isolator between your IP cam and your extrenal triggering circuits.
One of the reasons I like the Compro IP60 is its excellent manual. There is the best I've seen of its kind, and has some general notes for you on connecting external triggers.
For more help with basic electronics, see my Basics of Electronics page, which has links to lead you to all sorts of fun places.
Connecting external electronics is not particularly difficult. The IP cam acts as a toggle switch. There will be at least two places to connect single wires. Inside the IP cam there will be electronics equivalent to a switch. Sometimes that switch will be "open", and others it will be closed.
Note that I said "at least two..."? Sometimes there are three. This is the case when the IP cam offers both a "normally closed" and a "normally open" digital output. (Some IP cams have just two terminals for digital output, but the output can be configured through the camera's software to be normally closed or normally open.
Do not assume that you can connect "just anything" to the digital output connection. That way lies fried IP cams or worse. There will always be a limit to how "strong" the switch is. There will be a maximum voltage which should not be exceeded, and a maximum current which should not be exceeded. Often you will see a "power" limit, too. Let's say that your IP cam's digital output is rated for up to 25v, 500mA, and 500mW. (Those are, respectively, the voltage, current, and power limitations.) Can you attach a device running on 25 volts which will result in a 500mA current through the switch inside the IP cam? NO! That would be a case of it trying to handle 12.5W! (I think... "experts"... please check my arithmetic, and email me if you spot a problem, or indeed if you think I got it right!. Yes... I know... the specs I chose for the example are unlikely to arise in real life... they were just for illustrative purposes!) (These voltage/ current/ power things are not rocket science, but you do need to get them right. For more help, see my Basics of Electronics page.)
Whew! Disappear down a "rabbit hole"? Moi?
Don't be downhearted! If your IP Cam doesn't have the power to switch on a 500W siren and ten 5 kilowatt floodlights, there are simple answers... based on relays for the simple-minded among us, and SCRs for the more technical. Do be Very Careful before you mess with household electricity, though, please. If the chance of killing yourself or others seems a bit too remote to get your attention, also consider that if you cause a fire, your insurance company may not be willing to pay for something caused by amateur electrics. I've also written a page on controlling household electricity.
Here are a few cameras which have digital I/O of the sort we have been discussing. If you know of others, unless they are further badges of the Wansview/ Foscam generic, please get in touch! The links take you to pages by me about the individual cameras. Each page opens in a new tab or window to make getting back here easy.Compro IP 60 Foscam/ Wansview NCB541
Page WILL BE tested for compliance with INDUSTRY (not MS-only) standards, using the free, publicly accessible validator at validator.w3.org. Mostly passes. There were two "unknown attributes" in Google+ button code. Sigh.