# New guy - best video selection circuit help

#### Samsamedwin

Joined Jul 19, 2019
4
I have a basic understanding of circuitry but I need help with a practical issue.

My system is set up that I have two video signals (coming from a 5.8 GHz receiver - but these have already been converted to regular NTSC signals).

I also have 2 signals coming in which tell me which one of the NTSC signals (of the 2 above ) is stronger.
So in total - I have 4 signals.

What I want to do is send ONLY the best video signal through to an analog video output based on the signal strength signals I have.

I am wondering can I use a simple circuit like this one attached to do this? Is there a way to use a comparator to give me a 0 or 1 to send to a transistor or do I have to use something like an Arduino to compare the singable and give me a 0 or 1 so I can send it to a transistor to let one or the other video signals through.

The biggest question is can you even send a ntsc video signal through a transistor circuit and have it come out the other side in tact?

Worry if this is confusing or there’s really stupid questions in this post, I “get” circuitry but I don’t know it’s limitations with sending signals through.

Thanks in advance for any help.

#### Attachments

• 103.5 KB Views: 10

#### Dodgydave

Joined Jun 22, 2012
10,359
You can send a video signal through an Emitter follower to the output, or for Multiple signals i would use a CD4016 quad switch.

As for detection of the strongest signal, you need to compare the amplitude of the CVBS.

#### Alec_t

Joined Sep 17, 2013
12,886
Welcome to AAC!
If the signal strength is varying, do you want the circuit to be constantly switching between the two sources, or do you want some latching arrangement to prevent that?

#### Samsamedwin

Joined Jul 19, 2019
4
Welcome to AAC!
If the signal strength is varying, do you want the circuit to be constantly switching between the two sources, or do you want some latching arrangement to prevent that?
Great question. I want the circuit to constantly switch back and forth, to change when the best signal is available, giving me the best signal. I was going to use a 393 Comparator (now I realize I don’t need an Arduino to do that when a simple LM393 will do the trick for me)
I want to use one NPN and one PNP transistors as a switch to turn on only the best signal and send it along.
I am more just not sure if the video will make it through a transistor and then diode and stay in tack.
I’m taking my first class on electronics and going back to my physics knowledge from College - it’s interesting how you get a basic understanding by learning- and a GOOD understanding by DOING
.
Looking forward to building more real world use circuits!

#### Samsamedwin

Joined Jul 19, 2019
4
You can send a video signal through an Emitter follower to the output, or for Multiple signals i would use a CD4016 quad switch.

As for detection of the strongest signal, you need to compare the amplitude of the CVBS.
I looked up the CD4016 and that looks interesting!
Would that chip be able to switch the signal to the “best” one?
I like to learn and would love to know what setup might give that type of switching.
Thanks!!

#### Samsamedwin

Joined Jul 19, 2019
4
You can send a video signal through an Emitter follower to the output, or for Multiple signals i would use a CD4016 quad switch.

As for detection of the strongest signal, you need to compare the amplitude of the CVBS.
I want you to know when I asked about what configuration on the CD4016-I’m not lazy and I do “DYOR”.
It’s just that the data sheet says there’s a “control” pin- but makes no reference as to HOW to control it... is it a specific voltage that turns the switch outputs? Is each control relative to another “control”? ... or do they each control an output independently.

If you don’t know I get it- there’s millions of ic/chips available.
Any help I’d appreciate and not taken for granted...
Thanks!

#### crutschow

Joined Mar 14, 2008
30,086
It’s just that the data sheet says there’s a “control” pin- but makes no reference as to HOW to control it.
Of course it does.
Look at the data sheet excerpt below:

#### Audioguru

Joined Dec 20, 2007
11,248
You do not show a circuit that detects the "strengths" of the video signals. Each signal probably needs a peak detector to give a DC output of the amplitude of the sync pulses. Then the Arduino can compare the peak detector outputs and drive the Cmos switch.