Can you use a 4066 as composite video source switcher? - Page 1
Forum section: electronics / beginners

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: November 07, 2012, 07:13:26 am
content: I like to know if you think it's possible to use a 4066 to switch at least two different composite video sources.I've looked around a bit here and elsewhere. Can find a circuit for doing this. Maybe the IC can't do it so well.Rather than using a relay, is there an elegant electronic solution? It's for surveillance/recording and I don't want a relay operating every three seconds. Prefer not to buy a 'box' solution- rather build myself.I understand, just like using a hard switch, the video sync would be upset for a moment when switching. But could this device be used to select between two video signals without too much signal degradation?Do you have any experience with switching video with this device or any others?

author: RCMR
author_rank: Frequent Contributor
timestamp: November 07, 2012, 07:40:18 am
content: Yes, I use the 4066 in my 4-channel diversity controller project (I'll be doing a build-video in the next week or so).There is a minor amount of video bandwidth loss -- but hardly perceptible in most cases.I think you'll find there are different versions of the chip that have different stated bandwidths -- get the fastest one.

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: November 07, 2012, 08:09:51 am
content: Cool. Please lemme know when said video is out.Is there any/much circuit processing? Or do you just feed the signal straight into the input pin of the IC?

author: jeroen74
author_rank: Frequent Contributor
timestamp: November 07, 2012, 10:18:47 am
content: Video signals can have negatives voltages, so you need a negative power supply rail.

author: SeanB
author_rank: Super Contributor
timestamp: November 07, 2012, 03:47:24 pm
content: You can do it, just you need to have the incoming video terminated into 75R and then AC couple it with a 100uF 16V electrolytic ( low ESR one of course) into the chip, with a pair of 10k or so resistors to bias the input to half rail. You do need a video buffer on the output with a high impedance input and Ac coupled with a clamp diode to drive any cabling afterwards, but most will do the job easily. The trick is not to try to pass any current through the switch, just the voltage. If needed the buffer can be just a darlington pair with the emitter connected to a 75R resistor and develop the output video across this straight. Works well off a 5V rail single ended with the 74HC version. Slight loss and there will be a small amount of bleedthrough from the unswitched channels ( only noticeable on a input that has no signal where you will see some noise on a scope but no video signal) but good enough to switch cameras for a surveillance system.

author: poptones
author_rank: Frequent Contributor
timestamp: November 07, 2012, 07:03:57 pm
content: I've torn apart a lot of tvs and vcrs, never saw a "good" coupling capacitor. Just a plain ol' 47 or 100uf cap...

author: RCMR
author_rank: Frequent Contributor
timestamp: November 07, 2012, 08:54:29 pm
content: It's been my experience that most modern devices are very tolerant of voltage levels and capacitive coupling works just fine.