videoswitcher

Some years ago, in the haydays of VHS video, I designed and built a video monitor for a copybank of 100 videorecorders. That is 100 inputs for composite video and 100 stereo audio inputs.
I used a master controler and 4 slave units. The slave units have 24 audio/video inputs.
The controler has 8 audio/video inputs. The hardware for the slave units and the controler is identical, they only have different firmware.

On the controler board is a simple 16F84 pic which drives the shift registers on the switcher boards. That is the 18 pin socket, the 8 pin socket is for additional flash rom.



The slave units are controled via a simple ascii protocol, basicly I send the number of the required input. The slave units are daisy chained, the first slave accepts the ascii code, if the code is within its range (of 24) it selects the appropriate inputs and issues a code to switch of the 'downstream' slaves. If the received code is out of its range it substracts 24 of the received number and forwards the message. It also switches off any selected inputs.

There is a setup menu for the master controler, it attributes one of its inputs to a range. Selection 1 to 24 belong to input 1 etc, inputs 5 to 8 have a range of 1 for the selection of device 97 to 100.
Selection of a recorder is via a wheel and a select button. There is also a menu that allows you to autoscan a selected range.

Below is a photo of the master controler.


I am no HF guru but this little baby came in handy to check the bandwith of the switcher.