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How to make a input selector?

I'm looking to make a rather large input selector for a propose project a coworker is looking to commission me to make. I know I can buy a board that will be able to handle about four, but I need about 20 or so selections.
I'm looking to make your basic AV selection box, where if you press a button, any other pressed button will be released. Any help is greatly appreciated! 

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First do you want digital or analog? (This is important.)

To be sure how do you want the circuit to function?

You want a different button for every response and to turn off the last selection.

So you want the button to reset all to 0 and the selection you want to 1.

And you want the circuit to do this for 20 possible inputs to one output.

Is that correct?
gmxx3 years ago
My recommendation would be to use the 4310 series chips cascaded together with an arduino and a shift register or i2c expander. 20 or so sources is a lot of inputs, and wont be easily handleable via a purely mechanical method.

http://datasheets.maximintegrated.com/en/ds/MAX4310-MAX4315.pdf
DoctorWoo (author)  gmxx3 years ago
Well, now I feel silly. Didn't even think to use an arduino.
Probably some stupid follow up questions, but how many inputs could this manage (per chip, that is)? And could I manage to get four inputs, as to allow the RGB and a power connection per selection?
gmxx DoctorWoo3 years ago
max amount per chip would be 8. so you would need to cascade the chips, so that the output of one of the 8 chips would be fed into another 4 input chip.

depending on design, this could handle virtually infinite inputs. I remember seeing a design that cascaded 255 inputs.

Im not sure what you mean by four inputs, to allow rgb and power, but maybe. these chips are designed to only switch the video signal. you could possibly achieve what you are describing via other means.
Would you cascade them ? What happens to SNR ?
if he wants to switch 20 sources, the chipsare going to have to be cascaded. I havent seen a video switching chip that can handle that many inputs.

SNR?
Signal to noise. you're going to degrade it each time it goes through an amp.

I'd use two 4315's, and a 4314 perhaps and use the shutdown pins with the address MUX.
DoctorWoo (author)  gmxx3 years ago
Alright ,perfect. I know you can daisy chain them, as I'm looking to do that with a MAX 7115 (LED driver one).

As far as the four input thing, I suck at explaining. But what I'm trying to do is make it so you have your three color input for a component (for say a VCR or gaming console) and a power, which would turn on four LED's.
Separate jobs: Use the 7115 to do the signal switching, and a 7221 to light LEDs
That should have been the 4315, not the 7115, and, if we're going Maxim, then use a Max7301 to drive the mux on the 4315 (8 inputs IIRC)
steveastrouk is right. they would be separate jobs, which you handle in software.

if you are trying to switch RGB video, you may need to use a different IC for the video. the max 4310 is designed for composite video.
See MAX7300 (I2C) or MAX7301 (SPI) Personally I prefer SPI.