4 channel video switch

[numlock]

Hi there!

I need a small, waterproof, 4 channel video switch but I doubt there is anything available off the shelf. I have built a unit which uses waterproof push-buttons and uses latching relays but it was a nightmare to wire and ended up being unreliable and larger than I really want, so I want to do this properly with some sort of analogue switch IC.

 

The spec is fairly simple - 4 channels of composite video in and one channel out. Momentary push buttons to select each channel, with an LED to indicate which channel is selected. 12v power supply, as that's what powers the cameras.

 

There's no need to do anything clever such as vertical interval switching, but the signals shouldn't be degraded when they go through the switch.

 

I've had a fairly good Google for a circuit to do this but haven't found anything yet.

 

Can anyone suggest anything?

[Ike]

Whats wrong with a good old fashioned physical switch?

[gnomatron]

does it have to be totally waterproof? You could consider bagging up a V4 if it's a temporary job and you just need splash/rainproofing - the buttons are fairly big so you could probably use it through a clear plastic bag. Not that I've ever tried mind you. You can set the buttons to latch across rather than using the T-bar.

[numlock]

Physical switches are too big for my application and can't be waterproofed adequately.

This switch needs to be IP67 (ideally IP68). I can source small IP67 push buttons and encapsulate the rest to make it really strong and watertight.

 

I thought there would be an IC out there somewhere with most or all of the switching functionality built in, so I could mount it on a very small pcb and that would be that, but it's proving to be elusive...

[boatman]

Try this:

 

http://www.gennum.com/video/products/gx214a.htm

 

You can't get much smaller than that.

 

John

[numlock]

That looks interesting... what else would I need to make it all work? Can anyone draw me a circuit diagram?

[boatman]

That looks interesting... what else would I need to make it all work? Can anyone draw me a circuit diagram?

 

The datasheet for the GX434 has a circuit diagram including a suitable output buffer. Don't forget that you need a gain of at least 2 to allow for the 75ohm source resistance.

 

http://www.gennum.com/video/products/gx434.htm

 

From Gennum's website:

 

Applications Support - UK & Europe

Tim McBride

Phone: +44 (0) 1252 747000

Email: tim@gennum.co.uk

[dosxuk]

We use these and these ICs from Maxim. They have the added bonus of sending out free samples if you only need one or two.

[numlock]

This is where I need the help... I'm not too bad when it comes to understanding the circuit diagram, but translating that into a component list and pcb layout is where I struggle (although I have made a couple of very simple single sided pcb's in the past using some simple design software).

 

if any of you want to earn a few quid on the side, I'd be happy to pay a reasonable fee for someone to produce a pcb design (preferably single sided to keep the manufacturing costs down) and component list for me.

 

Feel free to PM me, letting me know how much you'd charge and how long it would take to do.

 

Just to be clear, you don't have to worry about the enclosure, connectors or the push button switches themselves. I just need help to get the pcb and components mounted on it right. There will be a DC power supply of 12V available so any step down/regulation would need to be included.

 

It all needs to be kept as small as physically possible. No wasted space on the pcb and components selected to keep the size to a minimum (although I don't want to go to surface mount components at this stage) .

 

Thanks again!

[boatman]

We use these and these ICs from Maxim. They have the added bonus of sending out free samples if you only need one or two.

 

I have used the Maxim parts and they are excellent, but do require a dynamic setup. The Gennum parts only need static logic control inputs which can be derived from a rotary switch or push buttons. I think that's much closer to numlock's needs.

[dosxuk]

Some of the maxim parts are the same, e.g. MAX 454, requiring only a BCD control input. We had an 8x1 matrix run from a rotary switch (until we upgraded it with a processor so it can be controlled serially).

 

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1565

[bh00]

I've been playing around, seems possibly to fit all the required components onto a 2" by 2" double sided PCB without resorting to any SMDs or compromising on ground planes. The issue I'm having is deriving the +-8v supplies needed for the gennum chip with only a +12vdc supply. I think some sort of 555 charge pump is in order!

Just as an additional note: Where is the best supplier in the UK of the GX434s?

 

Ben

[boatman]

I've been playing around, seems possibly to fit all the required components onto a 2" by 2" double sided PCB without resorting to any SMDs or compromising on ground planes. The issue I'm having is deriving the +-8v supplies needed for the gennum chip with only a +12vdc supply. I think some sort of 555 charge pump is in order!

Just as an additional note: Where is the best supplier in the UK of the GX434s?

 

Ben

 

It can be anything from +/-8V to +/-12V. All you need is one of these:

 

TMA1209

 

The UK distributor for Gennum used to be DT Electronics (See here) but the website link on there seems to be dead.

 

 

This is from the Gennum website:

 

Gennum UK Ltd.

25 Long Garden Walk

Farnham

Surrey, England

GU9 7HX

 

Phone: +44 (0) 1252 747000

Fax: +44 (0) 1252 726523

Email: gennum-uk@gennum.com

 

HTH

 

John