Re: Fail-safe VGA buffer

On a sunny day (Wed, 27 Oct 2010 16:34:12 +0200) it happened "F. Bertolazzi" wrote in :

If I was in China, then I would make some small spring metal strips that would contact the PCB... with a coil to lift those if power... There are non-coaxial relays with very low capacitance too.

Jan Panteltje:

Well, I might think about it, since it would be operated sparingly if at all, but I need a DPDT for each of the 5 channels for disconnecting both input and outputs.

But dimensions and prices are about the same.

Do you think I'm going to waste my time if I try to experiment with a video op-amp in inverting configuration with an input resistor of about 1k?

The 1k resistor would be a good enough "isolation".

On a sunny day (Wed, 27 Oct 2010 18:12:54 +0200) it happened "F. Bertolazzi" wrote in :

No, not sure that would be OK. Without power the chips must be able to handle current (in the limiting diodes). OTOH 1 k at 500 MHz needs only a small cap to form a lowpass. I dunno the input capacitance of your chips. Check that RC time.

Almost any small signal relay will do. Just make sure the users choose a 60Hz refreshrate. Higher is no use with today's flat panel monitors.

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why both in and output?

deo

iodes).

how about fig.3 in the ad8075 and relays on the supply pins ?

-Lasse

Jan Panteltje:

diodes).

One particular op amp claims that its impedance goes very high without power, but the feedback resistor remains.

The datasheet says that the non-inverting input has 1 pF capacitance, that would amount to about 160 MHz. :-(

And anyway the 0.1 dB gain flatness, that I read somewhere is the maximum allowable for good results, is up to just 100 MHz, at 400 MHz is -3 dB.

Geez, I hate relays.

On a sunny day (Wed, 27 Oct 2010 19:07:10 +0200) it happened "F. Bertolazzi" wrote in :

diodes).

Battery backup? Li-ion?

snipped-for-privacy@fonz.dk:

The thing must be fail-safe.

Because a broken or unpowered AD8075 would kill the signal.

Or not?

Don't forget the plastic springs.

Cydrome Leader:

In the coax relays?

Can you run your source to splitter A, screen #1 on output A1, splitter B on output A2? Then the splitter B can collect bullet holes, and you don't lose image on screen #1.

Jan Panteltje:

I'm afraid that's not enough. I will check with the customer, though. But there is the usual governmental Agency hanging around, that, since they have no idea of what they really want (apart from annoying people), will certainly want something impossible, or expensive, or both.

whit3rd:

The problem are the bullets into splitter A. Anything we connect to the VGA cable must be harmless to the signal.

On the other hand, you may say, if a relay does not work...

diodes).

Long time ago I made a box that uses a pair of 4-way signal relays to switch VGA video signal from one of two sources to monitor, I don't see any video artifacts (no obvious smearing of vertical lines) from the signals going through the relays. The relays are 4-way quality telecomms style.

Grant.

Grant:

Can you please tell me the model or at least the brand?

Nico Coesel:

The ones I found are priced similarly and have the same dimensions.

I can't.

Thanks.

Why not? What kind of refreshrate are they using?

Nico Coesel:

I don't know. I may ask, but I found some 2 GHz relays, $5 apiece that will do the job at any refresh rate.

Sorry for delay:

| [m]Aromat 9604A | DS4E-S-DC12V 0.6A 125V AC | 0.6A 110V DC | 2A 30V DC | MADE IN USA (UR) (SA)

The [m] is a logo looks like upside down 'w' on black rectangular background, (UR) is that ubiquitous safety mark, the (SA) is 'SA' inside a 'C' bottom right corner. Plastic case is yellow top, black underneath.

I can post photos if you need more info.

Grant.