Today's Message Index:
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1. 05:47 AM - Re: Re: Constructing an automatic RCA video camera feed splitte (Alec Myers)
2. 07:37 AM - Re: Re: Constructing an automatic RCA video camera feed splitte (Robert L. Nuckolls, III)
3. 08:19 AM - Re: Re: Constructing an automatic RCA video camera feed splitte (Robert L. Nuckolls, III)
4. 09:43 AM - Re: Re: Constructing an automatic RCA video camera feed splitte (Alec Myers)
5. 02:59 PM - Re: Re: Constructing an automatic RCA video camera feed splitte (Robert L. Nuckolls, III)
Message 1
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| Subject: | Re: Constructing an automatic RCA video camera |
feed splitte
I think were ok. That section is either wrong, or badly written, I cant work out
what its trying to say either. But:
Look at table 1 in para 8.4 - control L gives High-Z at the output.
9.2.1 says Avoid bus contention because it can drive currents in excessof maximum
limits. - its clearly anticipated as a bus driver IC.
On the left of figure 16 shows output pins 2,3,9 and 10 tied together to form
the output of the 4-channel mux in the sample application circuit.
AD8184 also needs a split supply. I dont think youll find any CMOS devices that
will switch an analog signal outside the supply rail, its not compatible with
the tech.
> On Oct 19, 2017, at 2:04 AM, Eric Page <edpav8r@yahoo.com> wrote:
>
>
> Gentlemen, we have a problem. Unless I'm very much mistaken, the CD4066 is not
going to work. I'll be quite happy if someone will tell me I'm wrong, but...
>
> In the CD4066BE datasheet (http://www.ti.com/lit/ds/symlink/cd4066b.pdf), at paragraph 8.1 it says,
>
> CD4066B has four independent digitally controlled analog switches with a bias
voltage of VSS to allow for different voltage levels to be used for low output.
Both the p and the n devices in a given switch are biased on or off simultaneously
by the control signal. As shown in Figure 17, the well of the n-channel
device on each switch is tied to either the input (when the switch is on) or
to VSS (when the switch is off). Thus when the control of the device is low,
the output of the switch goes to VSS while when the control is high the output
of the device goes to VDD.
>
> I read this to mean that we can't tie eight outputs (from two ICs) together into
a common VIDEO OUT bus because one "on" channel will be driving a video signal
into seven others that are sitting at -5V. This IC is four independent analog
switches; tying their outputs together looks like a recipe for silicon smoke.
>
> It gets worse. At paragraph 8.2 (3) it says,
>
> Normal operation control-line biasing: switch on (logic 1), VC = VDD; switch
off (logic 0), VC = VSS. [VC is control voltage.]
>
> So, the switches in this device don't turn fully off at 0V; they must be driven
to Vss (-5V). Obviously, the PIC can't do that. At paragraph 9.2 it presents
a typical application very similar to this effort, and suggests using the
CD4054B CMOS LCD Driver to level-shift 0 to +5V digital signals into -5 to +5V
signals. That's two more 14-DIP ICs, but it doesn't solve the first problem.
>
> I think we're stuck with the AD8184, as it's a proper 4-to-1 multiplexer.
>
> Thoughts?
>
> Eric
>
>
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=473672#473672
>
>
>
>
>
>
>
>
>
Message 2
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| Subject: | Re: Constructing an automatic RCA video camera |
feed splitte
At 07:45 AM 10/19/2017, you wrote:
>
>I think we=99re ok. That section is either
>wrong, or badly written, I can=99t work out what
>it=99s trying to say either. But:
>
>Look at table 1 in para 8.4 - control L gives High-Z at the output.
>9.2.1 says =9CAvoid bus contention because it
>can drive currents in excessof maximum
>limits.=9D - it=99s clearly anticipated as a bus driver IC.
>On the left of figure 16 shows output
>pins 2,3,9 and 10 tied together to form the
>output of the 4-channel mux in the sample application circuit.
>
>AD8184 also needs a split supply. I don=99t
>think you=99ll find any CMOS devices that will
>switch an analog signal outside the supply rail,
>it=99s not compatible with the tech.
>
Agreed . . . I think the 4066 will work . . . and
unlike my earlier assertion about paralleling
outputs of a PIC, this chip's outputs go to
a hi-z state when OFF meaning that an unselected
channel will not load the output . . . further
more than one channel can be on at a time when the
application calls for mixing the two signals.
The 4066 would be difficult to control in a bi-
polar supply . . . but a single 5v supply should
suffice.Your signal of interest has to stay between
the rails. Standard NTSC video is 1 volt pk-pk. The
cameras I looked at seemed to be happy running
from 3.3v supplies . . . hence quite capable of
1v pk-pk output.
Image result for ntsc video waveform
We don't know if this cameral video is capacity
coupled (floating DC reference) or DC stable. I suspect
it is capacity coupled; not DC stabilized. So
you might want to put 1K/1K voltage dividers on
the analog inputs to the 4066 to keep the 1v pk-pk
signal centered between the rails. If the cameras
are DC stable, they probably DC restored on the
lowest excursion of the sync pulse so that the
range of video signal voltages is more positive
than zero and much less than 3.3v. So all you
need to worry about is keeping the signal pretty
much centered between the Vss/Vdd rails.
Bob . . .
Message 3
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| Subject: | Re: Constructing an automatic RCA video camera |
feed splitte
> Standard NTSC video is 1 volt pk-pk. The
> cameras I looked at seemed to be happy running
> from 3.3v supplies . . . hence quite capable of
> 1v pk-pk output.
>
>Image result for ntsc video waveform
>
>
> We don't know if this cameral video is capacity
> coupled (floating DC reference) or DC stable.
I've ordered an exemplar 3.3 to 5v camera
from US supplier. I'll characterize the video
output and post findings to the list.
Bob . . .
Message 4
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| Subject: | Re: Constructing an automatic RCA video camera |
feed splitte
How about floating the PIC power rails to -1.8V/+1.8V ? Or +2.5/-2.5V Youre going
to have to generate a PIC voltage supply somewhere, regardless.
On Oct 19, 2017, at 10:36 AM, Robert L. Nuckolls, III <nuckolls.bob@aeroelectric.com>
wrote:
At 07:45 AM 10/19/2017, you wrote:
>
> I think were ok. That section is either wrong, or badly written, I cant work
out what its trying to say either. But:
>
> Look at table 1 in para 8.4 - control L gives High-Z at the output.
> 9.2.1 says Avoid bus contention because it can drive currents in excessof maximum
limits. - its clearly anticipated as a bus driver IC.
> On the left of figure 16 shows output pins 2,3,9 and 10 tied together to form
the output of the 4-channel mux in the sample application circuit.
>
> AD8184 also needs a split supply. I dont think youll find any CMOS devices that
will switch an analog signal outside the supply rail, its not compatible with
the tech.
>
Agreed . . . I think the 4066 will work . . . and
unlike my earlier assertion about paralleling
outputs of a PIC, this chip's outputs go to
a hi-z state when OFF meaning that an unselected
channel will not load the output . . . further
more than one channel can be on at a time when the
application calls for mixing the two signals.
The 4066 would be difficult to control in a bi-
polar supply . . . but a single 5v supply should
suffice.Your signal of interest has to stay between
the rails. Standard NTSC video is 1 volt pk-pk. The
cameras I looked at seemed to be happy running
from 3.3v supplies . . . hence quite capable of
1v pk-pk output.
We don't know if this cameral video is capacity
coupled (floating DC reference) or DC stable. I suspect
it is capacity coupled; not DC stabilized. So
you might want to put 1K/1K voltage dividers on
the analog inputs to the 4066 to keep the 1v pk-pk
signal centered between the rails. If the cameras
are DC stable, they probably DC restored on the
lowest excursion of the sync pulse so that the
range of video signal voltages is more positive
than zero and much less than 3.3v. So all you
need to worry about is keeping the signal pretty
much centered between the Vss/Vdd rails.
Bob . . .
Message 5
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| Subject: | Re: Constructing an automatic RCA video camera |
feed splitte
At 11:41 AM 10/19/2017, you wrote:
>
>How about floating the PIC power rails to
>-1.8V/+1.8V ? Or +2.5/-2.5V You=99re going to
>have to generate a PIC voltage supply somewhere, regardless.
>
don't think that will be necessary . . . let's
see what the video output on these cameras looks
like.
Haven't played with video since about '75 so I
had to dig into the history a bit. Given that
so much of the world runs on 5v . . . and given
the 3.3 to 5 v supply range of the cameras,
I'm pretty sure they're going to output
signals well inside the dynamic range of the
4066 running on a single rail, 5v supply. This
would make for a happy PIC as well.
Bob . . .
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