Help designing a video selector - Page 1
Forum section: electronics / beginners

author: David97
author_rank: Contributor
timestamp: September 23, 2015, 05:53:33 am
content: Hi everyone. I'm wanting to make a composite video selector that can choose from 4 video/audio different sources and give 1 output. I want this to have 4 tactile switches that choose the input. If a switch is pressed it will select that input until another switched is pressed.Because of the project, the bought ones aren't really that great. They use mechanical switches, so they can't be remounted where I would like.It would also be nice if it could remember what was it's last selected channel. So that when it is turned back on it starts on the same channel it was left on.I don't have a scope to test weather the signal is DC coupled or AC. But I have looked inside the devises that I'm planning on switching the video from. All of then are battery powered, I can see that the outside of the video cable is tied to ground, and I can't see a way that they would be generating a negative voltage to have a ac coupled signal.Since as far as I can tell the video is DC coupled. I'm thinking that I might be able to use a p-channel fet to switch the video. Then I would just use a arduino to turn on and off the signal. I would write to the the epprom to save what video signal was last chosen.Am I going about this the right way? Or would I be better to use a dedicated IC for switching the video. I've also considered using relays. But they are more expensive, need a fet to drive them anyway.I'm going to test tonight weather using fets will work.

author: helius
author_rank: Super Contributor
timestamp: September 23, 2015, 06:00:41 am
content: Look at Extron video switches, or Barco RCVDS units. I thought they were pretty well designed (they even have fast fade in/out when switching inputs).

author: JoeN
author_rank: Frequent Contributor
timestamp: September 23, 2015, 06:14:31 am
content: This guy uses a Maxim IC and he built the project up fairly professionally and says it works great. So you can use this design as a fallback, I guess:http://www.vwlowen.co.uk/radio/videoswitch3/index.htmThis is his third design, he has a transistorized and a relay design as well:http://www.vwlowen.co.uk/radio/videoswitch/http://www.vwlowen.co.uk/radio/videoswitch2/

author: German_EE
author_rank: Super Contributor
timestamp: September 23, 2015, 09:42:22 am
content: Composite video is normally DC coupled because things like sync separators look for the sync waveform between 0V and 0,3V with the rest of the video waveform occupying the space between 0,3V and 1V. Any CMOS MUX will be able to handle this signal and your only difficulty is the task of remembering which input was selected at the last power-down. You will probably need a CPU and some memory to do this which complicates the issue.

author: Wilksey
author_rank: Super Contributor
timestamp: September 23, 2015, 10:27:48 am
content: This one works, if you just pull out the switching part (the CD4051) I have built and proven this a fair few years ago now. No I am not affiliated blah blah blah, but I can guarantee it works for standard PAL composite signals.http://mondo-technology.com/vax.html

author: BradC
author_rank: Super Contributor
timestamp: September 23, 2015, 12:53:05 pm
content: Yeah, what he said ^^.We used 4051 or 4066 for video switching for years.. easy peasy. Even better when you are switching synced sources and you gate the switch on the frame sync so you get a clean switch and no roll.

author: David97
author_rank: Contributor
timestamp: September 24, 2015, 08:59:26 pm
content: Thanks guys. The cd4051 looks perfect for what I need. Cant wait until I get this project started, thank you so much!