Recently, a friend and neighbor asked me to assemble a camera system for him, the purpose of which was to provide video coverage of his entire front yard and the house.

His requirements included the ability to easily change the camera’s view (pan and tilt, zoom, and focus); the capability to automatically position the camera toward the garage door upon detection of the door opening or someone walking around inside the garage; and the ability to easily access the camera video via the Internet.

This system, then, represents the marriage of video, computer, and communications technologies, and is currently available for your inspection on our homeowner’s test bench at (9am ? 9pm PST)

This article describes that system and its components in sufficient detail to enable you to build your own.

System components.

This section lists the components of this system as it currently resides on the test bench, and with only a minor change, as it will be configured in my neighbor’s yard.

These components are as follows …

Camera. Because this camera is to be stationed outdoors and away from any building, my neighbor chose a conventional, rather than a dome camera. Virtually any camera will do, but this particular system uses a Panasonic WV-CP474 housed in a PELCO environmental housing. This color camera is sensitive to infrared (IR) illumination, and so with the proper illuminators, this camera will provide the capability to see in total darkness. This camera is equipped with a motorized zoom lens, and voltages received from the receiver-driver unit, drive the zoom and focus motors.

Pan and tilt mount. This system uses a PELCO PT570P/PP pan-and-tilt (p&t) mount, a rugged mount quite suitable for light-to-medium (up to 40 lbs) outdoor use. The (p&t) is connected to the receiver-driver, from which it accepts drive voltages that command one or both drive motors (pan, tilt) to move in one direction or the other.

Receiver-Driver. This particular unit is a PELCO LRD41C21, a very capable device. Its purpose is to receive message strings from the video server (i.e. from the homeowner’s computer LAN, or over the Internet), and convert those strings into voltages to drive the pan and tilt mount and the camera’s motorized lens (zoom, focus).

These message strings are in the form of what is known as PELCO ‘D’ code, riding atop an RS-422/485 connection. This device is also capable of using another form of communication in addition to the serial RS-422/485 connection. PELCO refers to that alternate communication form as ‘Coaxitron’, wherein the pan, tilt, zoom, and focus commands ride on the video line. However, for this application, where commands are coming in via LAN and/or the Internet, the RS422/485 link was the only choice.

So, the ‘gazintas’ to the receiver-driver unit, in this particular application, is an RS422/485 serial link, atop which rides pan, tilt, and zoom command strings encoded in PELCO’s ‘D’ protocol.

Because this particular application employs pre-sets, it also receives feedback voltages from the p&t mount and the camera lens. These voltages are analogous to p&t positioning, and lens state (zoom and focus).

There is still another class of input to this device: alarms – the outputs of external sensors. We’ll talk more about this shortly.

The corresponding ‘gazoutas’ from the receiver-driver are drive voltages routed to the drive motors in the p&t mount, and the focus and zoom motors in the camera lens.

It is important to note that whereas the LRD on the test bench is simply lying out on the bench, my friend’s outdoor application does not permit that luxury. His LRD must be housed within a watertight NEMA box.

Video Server. This and the receiver-driver unit are the heart, or perhaps more accurately, the brains of the system. This is a networked device linking the LAN (and optionally, the Internet) to the receiver-driver, and ultimately, the p&t mount and camera.

This unit has several functions?

1. Video Server. It accepts analog video from the camera (or alternatively, from the receiver-driver), digitizes it, and makes it available to the computer LAN (from which it may be made available to the Internet for direct or indirect viewing, posted on a website as images, or transmitted as image-bearing email).

2. Communications Bridge. The video server is responsible for interfacing the computer LAN with or to the video system. In fulfilling this role, it communicates with computers via the network in several ways. The usual method is HTTP, which is to say via an industry-standard Internet browser. However, it may also communicate via FTP (as either a client or a server to, for instance, upload images periodically or receive firmware upgrades); and via SMTP to generate image-bearing email. This particular server is an Axis 2401, but we also use the Advanced Technology Video V200, and we’d very much like to use the PELCO Net104a but haven’t yet had the opportunity.

The next step in the chain is one point where the test-bench differs from the actual application. While the actual application will be hard-wired between the Video Server and the LAN, the test bench uses a simple Linksys wireless Ethernet connection. One must balance the risk of system intrusion inherent in current wireless systems, with the disadvantages of stringing unsightly cables throughout a house or office. We chose the wireless link.

So, the video server is connected to a Linksys WET11 wireless bridge. The bridge, in turn, talks to a Linksys wireless access point, WAP11, several rooms and floors away. The WAP11 plugs directly into the LAN router.

LAN Connection. The LAN router is the heart of the LAN. It links each device on the network to each other, and to the Internet through a cable/DSL modem, thus enabling the devices to communicate with each other and with the outside world, i.e. the Internet.

That’s pretty much it as far as the equipment list goes. Now, regarding the wireless link between the Axis 2401 video server and the router, if you choose to use a wireless link in your LAN, there are security concerns you should be aware of. You can find more information about the equipment, and about the wireless security concerns via the links in the appendix.

Tying it all together.

Now, the preceding list should be all the equipment it takes to get your system up and on-line. However, there is one crucial element that’s missing, and you or someone you designate must create it. I refer, of course, to the cabling between the video server, the receiver driver, and the p&t / motorized lens.

Fortunately, this isn’t difficult at all. The manufacturers provide buyers with the connectors needed to interface the equipment, and with the documentation necessary to create the cables. All you need to do is sit down with the manuals, look for the connector pin assignments, and write down the information needed to come up with your own cabling diagram similar to fig. 1.

With that diagram, you can create your own custom cable or find a local company that can do it for you. Being in the Seattle area, for instance, if for some reason we cannot make the necessary cable, we’ll call on Redmond Cable ( to do it for us.

Alarms and external sensors

Alarms are simply the presence of a voltage (or ground) on any of several pre-assigned pins at either the video server or the receiver-driver. The application of that voltage (or ground) is an indication that an external ‘event’ has occurred: a garage door opening, for instance; a motion detector sensing the presence of an intruder; or a temperature reaching a specified level.

Your system can be configured to respond in one or more ways to any of these alarms – it can command the camera to cover an opening door, for instance. Or it can trigger image-bearing email to multiple recipients; it can even trigger a canned message to an SMS-capable mobile phone.

So it’s apparent that this simple system can provide a measure of convenience and security to the homeowner – especially if the video from this system is integrated into the home television system. With that integration, camera coverage may be viewed from any television in the home; and with the system integrated into the homeowner’s LAN, camera coverage may not only be viewed, but may be re-positioned from any PC in the house. And with the proper password, camera coverage may be both viewed and repositioned from virtually anywhere in the world served by the Internet (and these days, isn’t that everywhere?).