The Mux: Difference between revisions

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''The main mux'' is the huge black thing in the AV rack, it routes video to different places, and also has analogue TV demodulators in. The main mux is controlled by an outboard box which sits on the directors/vision mixers desk.
{{HDNO}}
{{Outofdate}}
 
The '''''main mux''''' is the huge black thing in the [[AV rack]]. It routes video to different places, and also has analogue TV demodulator inputs. It's controlled by an outboard box which sits on the Director/Vision Mixer's desk.


==Functions==
==Functions==
* 32 input to 4 output matrix
* 32 input to 4 output matrix
* 2 Nicam stereo tuners


==Faults & unknowns==
==Faults & unknowns==
2 composite inputs to the matrix are dead.
*2 composite inputs to the matrix are dead.
*Input 23 ad 32 are dodgy.
 
==Explanation of operation==
This was originally based around a PIC16F84 with an 8MHz crystal containing code written by [[hist:Rob Sprowson|Rob Sprowson]], the code for which is now lost.
 
A new PIC, a PIC18F2455 using a 20MHz crystal, has replaced this PIC through use of an extra 'daughter' board. This change in PIC was to allow easier coding, using C instead of assembler, and to provide USB capabilities. The source code has also been lost.
 
It now runs on an installed Arduino, and is one of the first [[YVP_Protocol|YVP Protocol]] compatible devices. This does mean a computer is needed to control it however, connected to the now real, RS-232 compliant serial port on the back.
 
==Power supply==
This is very much the weak point of the mux, and is tied up with why there are loads of unconnected [[BNC]]s on the back. - The Mux used to hold a distribution amplifier for creating 8 outputs of each main output from the matrix. Sadly though, this experienced some heavy cross-talk, and was misdiagnosed as "electric fields". The original creators now propose that simply adding better decoupling to the power supply would have solved the problem.
 
There are two mains transformers:
* 2x6V
**50VA
**powers + and - 5V rails


Red buttons have unknown function.
*2x6V
**3VA
**wired as 1x12V, 3VA to provide the +12V rail.


==Controller pinouts==
All the supplies are smoothed with big electrolitics, and then regulated with 78/79 series regulators.
{|border="1"
|-
!1
!+5V power
|-
!2
!0V ground
|-
!3
!32x4 crosspoint switch control lines
|-
!4
!consisting of a clock (rising edge trigger)
|-
!5
!CS (active-low) and Data
|-
!6
!NC
|-
!7
!Station Tuner control (I2C Data)
|-
!8
!Net Tuner control (I2C Data)
|-
!9
!Station/Net Tuner common control line (I2C Clock)
|-
|}


==explanation of operation==
All this is built on a length of chocolate block connector strip, with a lot of stranded hookup wire.
This was originally based around a PIC16F84 with an 8MHz crystal containing code written by Rob Sprowson. The hex file as loaded into the PIC can be found here[[https://ystv.york.ac.uk/~documents/docs_resources/StationDocumentation/muxController_sprow.hex]] whilst a partial disassembly of it can be found here [[https://ystv.york.ac.uk/~documents/docs_resources/StationDocumentation/muxController_sprow.doc]]. Also available is a disassembled version of the ROM code [[https://ystv.york.ac.uk/~documents/docs_resources/StationDocumentation/schedula_rom_disassembled.txt]] from within the BBC micro that used to be part of Schedula.


A new PIC, a PIC18F2455 using a 20MHz crystal, has replaced this PIC through use of an extra 'daughter' board. This change in PIC was to allow easier coding, using C instead of assembler, and to provide USB capabilites. The source code can be found in [[Main Mux Source Code]].
[[Category:Vision Path]]
[[Category:Home-Made]]

Latest revision as of 12:45, 6 August 2023

Template:HDNO

cancel.png Information on this page may be out of date or apply to old equipment. Use with caution.

The main mux is the huge black thing in the AV rack. It routes video to different places, and also has analogue TV demodulator inputs. It's controlled by an outboard box which sits on the Director/Vision Mixer's desk.

Functions

  • 32 input to 4 output matrix

Faults & unknowns

  • 2 composite inputs to the matrix are dead.
  • Input 23 ad 32 are dodgy.

Explanation of operation

This was originally based around a PIC16F84 with an 8MHz crystal containing code written by Rob Sprowson, the code for which is now lost.

A new PIC, a PIC18F2455 using a 20MHz crystal, has replaced this PIC through use of an extra 'daughter' board. This change in PIC was to allow easier coding, using C instead of assembler, and to provide USB capabilities. The source code has also been lost.

It now runs on an installed Arduino, and is one of the first YVP Protocol compatible devices. This does mean a computer is needed to control it however, connected to the now real, RS-232 compliant serial port on the back.

Power supply

This is very much the weak point of the mux, and is tied up with why there are loads of unconnected BNCs on the back. - The Mux used to hold a distribution amplifier for creating 8 outputs of each main output from the matrix. Sadly though, this experienced some heavy cross-talk, and was misdiagnosed as "electric fields". The original creators now propose that simply adding better decoupling to the power supply would have solved the problem.

There are two mains transformers:

  • 2x6V
    • 50VA
    • powers + and - 5V rails
  • 2x6V
    • 3VA
    • wired as 1x12V, 3VA to provide the +12V rail.

All the supplies are smoothed with big electrolitics, and then regulated with 78/79 series regulators.

All this is built on a length of chocolate block connector strip, with a lot of stranded hookup wire.

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