January 19, 2003
Updated May 29, 2003
New 5/29/04, make your own inexpensive (~$16) servo controller for use with a homemade pan/tilt webcam here.
New 2/11/03: See the "El Cheapo #3" parallel port audio/video switcher version (up to 40 cams) here.
This is version #2 of a homemade web controlled parallel port video switcher made from Radio shack parts. I use this switcher with the Ivista webcam software for webcam remote control. It can be used with other webcam programs, but you will need to make accomidations with a webserver CGI setup for web control (see zoomkat's home page for more info). This switcher is set up for 4 cam video/audios in, and one video/audio out to capture card and audio card. The schematic (bottom) shows for one parallel pin to switch a cam video/audio on/off using 2 resistors and 2 transistors. The combined output of 4 of these are connected at the video out and audio out RCA connectors for single seperate outputs to the video and audio cards. Only one parallel port pin is made high at a time so the video/audio signals don't interfer with each other. For the programming to control the switcher, go to the "El Cheapo" page to see how to control the parallel port pins. If you don't want or need web control and just want to switch the cams locally from your desktop, then just put the batch files (or shortcuts to them) found on the EL Cheapo page on the desktop. Double clicking the files/shortcuts will switch the cams. I've tested this with two types of Winnov capture cards and with a generic brooktree based capture card, and noted no problems. Nothing is guaranteed about this (but mine works), so you will have to experiment like I have. And as always..., YMMV!!!
Switcher demo page (as of 4/10/02) here
The Radio Shack parts for El Cheapo #2 (prices are approximate). Some components must be bought in a pack to get just one. They can be ordered cheaper from other suppliers, but if you want to tinker *NOW*, then the price difference isn't that much of a deal. ;-)
project box with circuit board 270-283 $4.00
4 4.7k resistors 271-1330 $1.00
4 10k resistors 271-1335 $1.00
8 NPN transistors 276-1617 $2.50
RCA 8 jack board 274-370 $3.00
1/8" mini plug 274-287 $2.00
RCA male plug 273-319 $2.00
25 pin male D plug 276-1547 $2.00
D plug hood 276-1549 $2.00
14' 4 conductor cat3 telephone wire 278-1310 $2.10
4 #4 X 1/2" flathead philips screws (home depot) $1.00
The basic how-to-do:
Get the parts and build the hardware: The parallel switcher is a simple one transistor/resistor per cam video/audio switcher. If you use the generic NPN radio shack transistors, lay one down with the flat side down and the 3 leads sticking out to the left. To the center pin (base), you connect a 4.7k resistor for video (a 10k for audio). The other side of the resistor is connected to the parallel port pin wire. The top transistor lead (collector) is connected to the center of the RCA connector comming from the cam video (audio), and the bottom lead (emitter) is connected to the other video (audio) transistor outputs. These are connected to the plug connector wire going to the video capture device (or audio card line in). All the grounds (RCA plug outside) are connected together, keeping audio and video seperated. Note that there are no connections made to the ground side of the parallel port connector (that would ground out the video and audio signals). For audio and video from a cam, you make two transistor setups that operate as a pair. The resistors for each are both connected to the same parallel port pin so they operate at the same time. Place the batch files (see the El Cheapo page for making the batch files and using debug.exe for testing) on the desktop and double click them to check out the operation of the parallel pins. If you want to make an 8 cam video only switcher, then you use 4.7k resistors with all 8 transistors, skip getting the audio plug, and run a second 4 conductor wire form the parallel port pins #6-9 to the second 4 transistor/resistor pairs, connect all the transistor outputs together, and on the RCA plug board, connect all grounds together.
The basic parallel port switcher #2 pix:
Below shows the soldering of the 4 conductor phone wires to the parallel port connector (connect to pins #2-5). If you are making an 8 cam version, you will need to use another piece of 4 conductor wire so there will be 8 wires comming from the parallel port connector (connect to pins #2-9). These wires are connected to the resistors on the switcher circuit board. The audio and video plugs are attached to seperate piece of 4 conductor phone wire which are connected to the common audio out and video out on the circuit board. If you are making the 8 cam video only version, you don't need the audio plug.
This is a pix of the project box. The top of the box has a ~1 7/8" X 1 1/8" hole cut in the top so the bottom of the RCA 8 jack board will fit flush with the box top.
This pix shows the back of the RCA 8 jack board. The video grounds are all connected together and the audio grounds are all connected together (if you are making an 8 video only switcher, connect all grounds together). The wires connected to the center of the RCA plugs are attached to the appropriate video/audio "in" transistor collectors on the circuit board. The ground wires are connected to the grounds on the video/audio plugs.
Below is a close up view of the circuit board. The top row of 4 transistors/resistors is for the video, and the bottom row is for the audio. The 4 wires comming in from the parallel port connect to the top row of resistors. A jumper wire is run from each of the resistor/ parallel port wire connections over to the resistor for the audio transistor (makes both audio/video transistors switch at the same time). The output (emitter) of the video transistors are connected together on the bottom of the board using a bare piece of wire soldered to each. The same is done with the audio transistor outputs. The video out and audio out to the plugs are connected to these bare wire headers. The grounds going to the plugs are connected to the grounds comming from the RCA 8 jack board. these are joined together on the circuit board.
Below is a close up of how the transistors and resistors are set on the circuit board. I keep them up off the board a bit so I don't fry them while soldering (makes for easier access when trouble shooting too). Don't set them so high as to hit the bottom of the RCA plug board. On the bottom of the board, I usually only solder one leg of a component to the board itself. This makes for easy unsoldering when you make a mistake. Once one component is soldered to the board with a little of its wire sticking out, I bend the next component's wire over to it and solder them together. In this project box, the wires on the bottom of the board have to be kept close to the board, as the bottom of the box is aluminum (don't want a short between components!)
This pix shows the audio/video in wires comming from the RCA 8 jack board soldered to the audio/video in side (collector) of the transistors. These wires need to be run through the hole in the box top prior to soldering to the board.
This shows the switcher box setup prior to putting it together. A small notch will be needed in the bottom edge of the box for the plug wires to go through. You have to kind of stuff the internal wires in to the box.
Below is the completed switcher. The RCA plug board is attached by drilling holes in the box top with a ~3/32" drill (test this first, as my drill isn't marked) and attached with the #4 X 1/2" flathead screws.
Below is the completed "El Cheapo #2" switcher connected to the local cable audio/video, satellite audio/video, pan/tilt cam video, and the 4th video connector being used to operate the "channel up" button on an IR remote control. The switcher plugs are connected to the parallel port, the capture card video in jack, and the sound card line in jack. Check it out here.
Schematic for one cam audio/video. Other cam audio/video pairs are paralled together at the video/audio transistor outputs.
