Bruce' FPV Diversity Controller project

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Re: Bruce' FPV Diversity Controller project

Postby Rixx » Sun May 20, 2012 1:58 pm

BillGriffiths100 wrote:Are you using 74HC high speed Cmos logic (or equivalent) or the older type?
If you are using the older type it's an order of magnitude slower that may be your problem.


It's HCF4066BE
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Re: Bruce' FPV Diversity Controller project

Postby rotorz » Sun May 20, 2012 1:59 pm

Also it might be worth asking which manufacturer makes 4066 RcModelReviews is using.
I know from experience identical chips made by different manufacturers can have different characteristics but still be within specifications.
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Re: Bruce' FPV Diversity Controller project

Postby Rixx » Sun May 20, 2012 2:02 pm

I'm sure I'm missing something essential, as I have zero experience in video signals procesing, just shooting in the dark here :)
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Re: Bruce' FPV Diversity Controller project

Postby BillGriffiths100 » Sun May 20, 2012 6:52 pm

It's HCF4066BE

That chip first came out in 1976 it most probably the cause of the loss of video pass-through.
Get a high speed version, your problem will most likely be solved.
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Re: Bruce' FPV Diversity Controller project

Postby RCModelReviews » Sun May 20, 2012 10:26 pm

Note that the Ron (resistance in the on-state) of the switch is nominally some 96 ohm so if you're driving a 75ohm video device you'll get some signal attenuation through the switch.

This hasn't been an issue driving any of the LCD displays or FatShark goggles to date but you could use a level/impedance shifter on each channel before the switch or simply use a higher-impedance non-inverting amp/buffer on the combined output.

If you've tied all four switch outputs together, make sure you've got only the active switch turned on -- if you've left any of the control signals floating they will likely turn the unused switches on and that could drag down your output signal significantly.
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Re: Bruce' FPV Diversity Controller project

Postby Rixx » Mon May 21, 2012 7:25 am

RCModelReviews wrote:Note that the Ron (resistance in the on-state) of the switch is nominally some 96 ohm so if you're driving a 75ohm video device you'll get some signal attenuation through the switch.

This hasn't been an issue driving any of the LCD displays or FatShark goggles to date but you could use a level/impedance shifter on each channel before the switch or simply use a higher-impedance non-inverting amp/buffer on the combined output.

If you've tied all four switch outputs together, make sure you've got only the active switch turned on -- if you've left any of the control signals floating they will likely turn the unused switches on and that could drag down your output signal significantly.


RON of my specific chip is 80-250 ohm, depends on supply voltage (however, I cannot find 0-5V RON in datasheet, just some other combos like 0-10, -2.5 - 2.5, etc.). I'll check datasheets of AC/ACT/HC/HCT series for some better RON.

I have two receivers, so I used two switches and everything else left floating. I'll fix that and see if I it works. If not, I'll either add buffer or buy integrated video switch.

Thanks!
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Re: Bruce' FPV Diversity Controller project

Postby BillGriffiths100 » Mon May 21, 2012 7:52 am

If you've tied all four switch outputs together, make sure you've got only the active switch turned on -- if you've left any of the control signals floating they will likely turn the unused switches on and that could drag down your output signal significantly.


Yes and don't forget to decouple the chip with a 100pF cap. Power supply noise feed-through can allow the gates to turn on and off decreasing the RON significantly
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Re: Bruce' FPV Diversity Controller project

Postby RCModelReviews » Mon May 21, 2012 9:15 am

100pF is probably a bit small -- I generally use 0.1uF (100nF) ceramic decoupling caps for best results.
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Re: Bruce' FPV Diversity Controller project

Postby Rixx » Mon May 21, 2012 9:53 am

Yup, I used 100nF too. I checked local parts shops, no HCT4066... I'll try to ground floating gates. If that won't help I'll google some buffer circuits. Or get another video switch IC from ebay :)
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Re: Bruce' FPV Diversity Controller project

Postby BillGriffiths100 » Mon May 21, 2012 4:29 pm

100pF is probably a bit small -- I generally use 0.1uF (100nF) ceramic decoupling caps for best results

Oops that's what I meant to put, just a few orders of magnitude out!(Ass!) :oops:
Last edited by BillGriffiths100 on Mon May 21, 2012 8:14 pm, edited 2 times in total.
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