1 button

pcleats · Joined: 12 Dec 2005

Hello,

I am new to micro controllers and I am wanting to create a video
switcher, and I need to be able to switch from one source to the
next source by pushing a single button. The logic table is:

a0 a1 Channel out
--------------------
0 0 0
0 1 1
1 0 2
1 1 3

I am using a max 454 50MHz (4:1) Video Amplifier and Mux to control
the source input

What is the best way to do this

I could do this with a 4017, but I want to display the info on an
LCD display.

Thanks for the help.

Patrick

dkinzer · Site Admin Joined: 03 Sep 2005 Location: Portland, OR

The solution to this problem depends a lot on what else needs to be done by the processor. In the simplest case, the processor is dedicated to detecting the press and release of the "next channel" button. You'd need code to read the switch state using GetPin(), increment the channel selector value, output the select value to two I/O lines that drive the video mux, and finally, wait for the switch to be released. There are some minor issues to deal with as well, e.g. dealing with contact bounce on the switch.

If the processor needs to be doing other things, the solution becomes a bit more complicated. In this case, perhaps it would be best to connect the "next channel" switch to one of the interrupt inputs of the ZX-24 and dedicate a separate task to responding to the switch closure.

If you tell us more about the entirety of what you want to do, a better solution may be suggested. It will also be helpful to let us know how much you already know about the solution (or parts thereof) and your experience level (e.g. hardware, software, etc.) so we don't describe the solution in either too much or too little detail.

pcleats · Joined: 12 Dec 2005

The project has come about because I have a video capture system that captures 16 channels of real time video. The problem that has been presented to me is that I need the ability to see as many as 24 cameras. I don't need to see them all the time. For example if I know a section is not going to be used I can switch to a different set of cameras. At least 12 of the cameras are always used.

I will need to build 4 units that will allow me to decide the set of cameras I am going to use.

I know a bit about the max454. I don't really need more then a 4 channel unit. I just need 4 4 channel units.

I want to be able to quickly switch from camera to camera. A push button seems like a reasonable way to do this. As I said a 4017 would do the job, but I want to be able to display information on an lcd display and the camera that is currently active. Also I would like to be able to switch from manual mode to automatic and then use a set of switches to determine the amount of time a camera is active.

I already know how to make the max454 do what it needs to do, I'm just not sure what I need to do the make the microcontroller do what it needs to do. I don't know much about programming (yet) I still get confused about where things need to go. I have been doing electronics for a few years. Just very new to programming and microcontrollers.

See attached for a visual concept

Thanks for the help.
Patrick

dkinzer · Site Admin Joined: 03 Sep 2005 Location: Portland, OR

With most embedded systems, you can make tradeoffs between hardware and software. For example, you could use an external counter clocked by a de-bounced switch and feed the low two bits to the video mux. You could feed those same two bits to the processor so that it could update the display to match.

On the other hand, you can have the processor detect the switch state-change, update an internal counter, output the two low bits to control the video mux and update the display. If you did this, you can make the code simpler by using the two least significant bits of one of the ports for the video mux select outputs. Here is a simple routine that increments the counter value and outputs it: