MAX4026 Woes

[MioTheGreat]

I've got a projector that takes both component and VGA input on the same Dsub15 plug. I use a mechanical switch currently, which works, but it's a crappy solution, introduces a lot of noise, and sometimes has to be hit to work properly. Mechanical switches suck, and I wanted to go solid state with it.

I saw this:
**broken link removed**

and decided to build my own VGA switch.

As the MAX465 is not available anymore, I redid it using a MAX4026 (It's mislabeled as MA4026 in my schematic), adjusting the pinout from the project in the link, but when I power it up, nothing happens. I've only got an Component device hooked up to it right now, so the other two ICs are not currently being used.

The only things not shown on this schematic is that there are 0.1uF ceramic caps in various places, a capacitor on the negative output of the MAX660, and the MAX660's negative output is actually hooked up. For the bypass caps, there's one under the chip that only uses the 0/5 supply, and 2 under each that takes -5/+5.

http://hid.com/dan/selectee.pdf

 

[MioTheGreat]

Well, I still haven't been able to solve this, and I don't have a scope here, but I just put my DMM on it (A fluke 87v), I'm getting ~200mVAC on the R component input, and only ~70mVAC on the output. So it's obviously not properly reproducing the signal.

 

[Nigel Goodwin]

You're trying to duplicate a mechanical switch electronically - and basically you're never going to get it as good.

If your mechanical switch has problems, then it's faulty - replace it with a decent quality one.

 

[MioTheGreat]

You're trying to duplicate a mechanical switch electronically - and basically you're never going to get it as good.

If your mechanical switch has problems, then it's faulty - replace it with a decent quality one.

Given that I'm trying to switch a component signal and an 800x600 SVGA signal, I don't think I should be having any problems. I'm not asking for much. It's not like I'm trying to switch a 1920x1200 signal here. That's got to be less than 30MHz, right? (I'm not 100% sure how to calculate the bandwidth for the signal)

Switching it electronically is really what I want, especially as the projector has a serial port control on it, so I can have the whole thing nicely automated.

 

[Nigel Goodwin]

Given that I'm trying to switch a component signal and an 800x600 SVGA signal, I don't think I should be having any problems. I'm not asking for much. It's not like I'm trying to switch a 1920x1200 signal here. That's got to be less than 30MHz, right? (I'm not 100% sure how to calculate the bandwidth for the signal)

Switching it electronically is really what I want, especially as the projector has a serial port control on it, so I can have the whole thing nicely automated.

You need wideband amplifiers, one for each connection, in order to buffer the impedances and increase the signal level - although the sync signal only needs a much lower bandwidth.

 

[MioTheGreat]

You need wideband amplifiers, one for each connection, in order to buffer the impedances and increase the signal level - although the sync signal only needs a much lower bandwidth.

I know. I thought I had it all set up correctly, but as it doesn't work...

 

[MioTheGreat]

I've decided to redesign this for 2 component inputs and 1 VGA input. So I'm going to keep the hardware for the sync/DDC as it is, as it only needs to enable or disable those based on whether or not the currently selected output is VGA.

Can anyone recommend a decent 3:1 or 4:1 multiplexing chip that will work with 3 inputs with enough bandwidth for component and 800x600 60Hz SVGA signals?



How I currently have it all hooked up (75 resistor in series with the output, and another 75 pulling the input to ground) is meant for something with a gain of 2, based on what I read in the datasheet. Can I do without them if I pick a chip with unity gain, or are they important?

 

[Mikebits]

The MAX4026 looks like a good choice. But I wonder if using analog mux chips for sync was. Perhaps a digital mux would be a better choice. Do you have a VGA spec? I would look at signal requirements Delays, levels, and such, but I should think what you propose is possible.

 

[MioTheGreat]

The MAX4026 looks like a good choice. But I wonder if using analog mux chips for sync was. Perhaps a digital mux would be a better choice. Do you have a VGA spec? I would look at signal requirements Delays, levels, and such, but I should think what you propose is possible.

I'll look at them, but I still haven't managed to figure out what's wrong with my MAX4026 setup. I'm not even using the sync yet, I'm just trying to pass through the RGB signals for component.

I suppose it's possible I damaged the chip during soldering (I don't do much surface mount work)...

 

[Nigel Goodwin]

I'll look at them, but I still haven't managed to figure out what's wrong with my MAX4026 setup. I'm not even using the sync yet, I'm just trying to pass through the RGB signals for component.

Presumably you are aware that RGB and Component are considerably different things? - you can't feed RGB to Component inputs.

 

[MioTheGreat]

Presumably you are aware that RGB and Component are considerably different things? - you can't feed RGB to Component inputs.

On my projector, YPbPr and VGA are fed in over the same cable.

I currently have a Component to VGA adapter (It's nothing more than a cable with the dsub15 plug on one end and the RGB RCA plugs on the other) that is one of the things I'm replacing with this switch.