Protect circuit from accidental application of power to A/V out port.

[ruthsarian]

I have an old video game console that outputs an RF video signal. My plan is modify the console to output composite video and audio so I can connect it to a device that doesn't have an analog tuner in it. My thought was to use a 3 or 4 conductor 1/8" phone jack (audio is mono so I don't necessarily need separate left/right audio lines) like you might find in some portable DVD players or camcorders.

The problem is that this console, a 1975 Atari Pong, has a power plug (called the "battery eliminator" as it was normally powered by 4 D-cell batteries) which uses a 2 conductor 1/8" phone jack. I'd like to protect the circuit from someone plugging in that 1/8" power adapter into the A/V jack. How would I do that? It seems a few diodes would be in order, but I'm guessing the forward voltage of the diodes would degrade the video and audio signals. Would that be the case? And if I could use diodes for this, would I need something special, like a low forward voltage, high frequency diode? Or is there another way? Maybe PFETs?

The simplest solution would be to not use the 1/8" jack for A/V and instead use RCA connectors. Maybe that's the way I'll go, but I'd still be interested to hear if there's a solution to using the 1/8" jack.

Thanks

[rstofer]

Composite signals ordinarily come out on RCA jacks and that solves the problem.

It may turn out that there are blocking capacitors on the video and audio signals (I wouldn't be surprised since they probably want to remove any DC bias) and plugging the power supply plug into the video output socket may not cause any damage.  I would want to know a lot more about the circuitry.

Perhaps a 1/4" audio plug?  Maybe a 5 pin DIN?

If there is room, I would opt for the RCA jacks since that is a standard.

[vk6zgo]

1/8" phone jacks are horrible,cheap,flimsy things at best, so I would recommend you steer well clear of them.
I don't like RCA connectors that much, but at least you can buy sturdier versions of them, which are OK.

Using the same type of connector for both power & A/V is asking for trouble, as is farting around with diodes on video & audio circuits.