The problem: 2 s-video sources, 1 s-video input to your TV .

Overview: A "Double Pole Double Throw" DC relay is used to switch two input cables to a single output cable. Power for the relay comes from an inexpensive DC power cube; which is plugged into a switched outlet on one of the source devices.

How it works:

Without any power to the relay, the (source #1) cable soldered to the relay N.C. contacts will be electrically connected to the TV cable. Then, when the relay is powered, the (source #2) cable to the N.O. relay contacts is switched to the TV cable. Only one source is connected to the TV cable at any one time.

My LD player has a switched AC outlet, thus this is where I plugged in the DC power cube. When I turn on the LD player, the relay energizes disconnecting the s-video cable (N.C.) away from the DVD player and connects to the LD player (N.O. cable). When I turn off the LD player, the relay relaxes, reconnecting my DVD player to the TV cable. I have had no problems at all with this setup.

1. Locate a good DC cube supply that was left over from a dead cordless phone or device; note the listed output voltage. Use this to purchase a DC relay at Radio Shack. If the cube supply outputs 5.5 to 7.5 volts, purchase a 6 volt relay; if it outputs 12 volts, then obviously purchase a 12 volt relay. (this saves you from purchasing a power source you probably already have).

2. The relay needs to be a DPDT DC relay at the determined voltage. A standard, simple relay will do.

3. Next you will need three s-video cables with male ends on one end of them. Picture having 3 cables coming from the "relay box" you will build. One goes to your TV s-video input; the other two go to your sources outputs, examples used are DVD and LD players. I had a long s-video cable and simply cut it into half. This took care of 2 of the 3 needed, and I purchased another. What you end up with are 3 cables with male s-video connectors on one end and bare ends on the other.

4. Strip the bare ends of the s-video cables about 2 to 3 inches. What you will see are two bare shields and two small wires (per cable). Connect all the bare shields together on all three cables; they are all grounds. The shields do not connect to the relay, only to each other.

5. Choose one s-video cable to connect to your TV input. Locate the two small wires from this cable, strip about ¼" insulation off and solder each one to the center contact of each pole of the relay.

6. Choose another cable for source #1 and solder its two small wires to the contacts labeled N.C. (normally closed) making sure of pin orientation.

7. The last cable, source #2, solder its two small wires to the corresponding N.O. (normally open) contacts on the relay; again making sure of pin to pin orientation.

8. Solder the two wires from the power cube DC cable across the coil of the relay, polarity not important.

Testing;

Use an ohm meter and make sure of pin to pin contact orientation between the TV cable and source #1, N.C. (being certain you did not cross any; pin 1 to pin 1, then pin 2 to pin 2, and so on………)

Then plug your cube supply into an AC outlet; now checking pin orientation on the TV cable and source #2 N.O. cable. (only two pins are actually switched; the other two are grounds and will always be connected)

I mounted all this in a small project box, notching holes for cable exits.

Want to get fancy? You could find female chassis mount connectors and wire them to the relay, mounting them on the project box. This allows you to use existing non-modified s-video cables; for those of you who just cannot cut the end off a perfectly good s-video cable.

Good Luck!

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