Using multiplexer IC to switch between analog cameras

Discussion in 'General Electronics Chat' started by ymg200, Oct 2, 2015.

  1. ymg200

    Thread Starter New Member

    Oct 2, 2015
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    Is it possible to use 4052 multiplexer to switch between analog cameras' signal?
    http://www.ti.com/lit/ds/symlink/cd4051b.pdf
    4052 has 4 pairs of switchable terminals, so I'm thinking that it might be possible to hook it up to 4 cameras (using Video and Audio signal from each camera).
    Here is a sample analog camera that I will be using:
    http://www.ebay.com/itm/HD-700TVL-S...ic-/181617525838?_trksid=p2141725.m3641.l6368

    I am currently using 4051 to switch between sensors that have the same address on I2C bus, and it works fine for me. However, I2C is digital, and I wonder if 4052 can handle analog camera signal with no distortion.

    Which series of 4052 would be better for switching cameras - HC, CD, or other?

    Thanks all!
     
  2. GopherT

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  3. crutschow

    Expert

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    What is the impedance of the video line you will be using, the standard 75Ω coax?
     
  4. AnalogKid

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    The 405x series of parts will work, but not well. The parts do not have a flat frequency response out to greater than 4 MHz (full video bandwidth), require both input and output buffering, and have a relatively high ON resistance which acts as part of a low pass filter with whatever external capacitance is in the circuit.

    Maxim, Analog Devices, and Linear Technology all have excellent video multiplexer chips that include both input and output buffers/gain correctors for driving 75 ohm cables directly. Maxim has an excellent reputation in this field.

    ak
     
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  5. ScottWang

    Moderator

    Aug 23, 2012
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    Analog signal → CD4051,Vdd=10V,Vee=0V,Vss=-10V → Analog output
     
  6. ymg200

    Thread Starter New Member

    Oct 2, 2015
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    The camera specs do say 75 Ohm, but my cable length is only 5" and I'm using regular wire rather than a coax. The wire goes from the camera to the 5.8Ghz AV transmitter. This is for an FPV RC model. My idea is to have multiple cameras looking in different directions and using a multiplexer connect either of them to the transmitter (rather than rotating a single camera with a servo mount).

    http://www.ebay.com/itm/HD-700TVL-S...ic-/181617525838?_trksid=p2141725.m3641.l6368
     
  7. AnalogKid

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    The AV transmitter probably has a 75 ohm input impedance. A 400 ohm resistance of a non-video analog switch will form an 80% attenuator.

    ak
     
  8. ymg200

    Thread Starter New Member

    Oct 2, 2015
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    Does the fact that I'm not using a 70 ohm coax (see my post above), change the affect of 4052 on the signal?
    Why input/output buffering is necessary? Is that to offset video glitches during mux switch times? If this is the case, then I can live with a short video glitch during mux switching since the video already has occasional interference from being transmitted over the 5.8Ghz AV link.
    Thank you.
     
  9. AnalogKid

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    It's not about glitches, it's about impedances. The ON resistance of a 4052 with +/-5 V supplies is between 150 and 250 ohms. That is 2 to 3 times greater than the output and input impedances of a video source and destination. That extra resistance creates a large signal attenuator that changes with the instantaneous signal amplitude, so there is both signal loss and distortion. With a true video multiplexer chip the attenuator is much better behaved and there is a high impedance buffer/gain stage built in to drive an external 75 ohm load.

    ak
     
  10. ymg200

    Thread Starter New Member

    Oct 2, 2015
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    Yes, the AVTx is matched to the camera signal.

    Taking your advice, I'm looking at MAX454 video mux.
    Circuit: http://www.glolab.com/freeinfo/images/videosw.pdf
    Datasheet: https://datasheets.maximintegrated.com/en/ds/MAX452-MAX455.pdf

    I can't figure out what is the connection in this circuit that goes to the IC between terminals 12 and 14. It looks like all pins in the IC are already used, and this one is not marked with a number. All schematics that I've found so far are just copies of this one, with this connection to an unmarked pin.
    Also, how do I provide -5V to pin4? I'm using a DC battery as power.
    Thank you!
     
  11. AnalogKid

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    Every pin is explained on the datasheet you link to. Pin 12 is the positive power supply input. Pin 14 is one input to the internal output signal driver. Notice the 6.8 pF capacitor on the schematic on page 6. It is the same on the application schematic even though that schematic is for a different chip.

    Somehow you need to come up with a -5 V power supply, either a power converter or a 2nd battery.

    ak
     
  12. ymg200

    Thread Starter New Member

    Oct 2, 2015
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    I understand those pinouts in the
    I understand all connections to signed pins in the schematic, except the one that does not have a pin number assigned to it. I have highlighted this connection in the picture below. All pins are already assigned in the picture (except pins 5, 6 and 9, which are NC), so I don't understand where in the IC the highlighted connection goes to.

    MAX454_schematics.JPG
     
  13. AnalogKid

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