One day I was asked to redraw the layout and video operating area of a medium‑sized television O.B. Van. The central video router, used also for camera technical control, was a Blackmagic Design (BMD) Compact Videohub.

The camera operational control panels (OCPs – named as such in the specific case of that equipment; may differ in other situations) were equipped with joystick type control for iris & master black adjustment, with the possibility of “Joystick Override” operating mode: individual per‑OCP contact closure when its joystick is pressed. Sometimes this is referred also as touchdown function or joystick preview.

This operating mode is described, better than I could do myself, in an old Leitch GPI interface user manual lying around here somewhere:

When a joystick is operated on a given CCU, the contact closure is made and that CCU’s router input is selected. When the joystick is released, the contact closure opens and the router automatically returns to the previously selected input, usually a studio program video.
(ref.: RCP- Series: RCP-GPI64/32p ... Operation/Installation Manual)

The Joystick Override mode works in conjunction with the video router to which those CCUs are connected, but my problem was that the BMD Videohub does not have a direct GPI input for such a functionality and their GPI & Tally Interface does not perform properly a Joystick Override function. In that forum discussion I was then recommended to try to build an Arduino-based interface and write my own commands.

Well, I took the recommendation seriously, but soon I became disappointed: right then Arduino discontinued the network module (“shield”) – at least that was the situation at their own shop by the time I was studying this variant – with the exception of the Arduino Yún version, which I considered not suitable for my purpose. Therefore, I abandoned the Arduino road.

Then, from the options available to me, the Raspberry Pi caught my attention: attractive hardware, generous GPI port, true Linux operating system that allows restricted access levels – a mandatory feature, in my opinion, for a network configurable broadcast equipment.

First tests sounded promising, so here I am: the project for Joystick Override solution for BMD Videohub router(s) has started. I wrote from scratch the entire Joystick Override function software, in Python programming language.

Because usually I like to keep the quality bar at a higher level than the average, I enforced the same tendency here – so these were my major architectural guidelines:

• the interface shall be rackmounted; loose wires and hanging equipments are to be avoided in any serious central apparatus room, let alone into an O.B. Van
• the power supply shall be internal, with power cord via IEC connector
• the internal power supply shall be reliable, slightly electrically oversized
• the interface shall be equipped with at least 16 GPI inputs, given that the O.B. Van from which it all started had provisions for at least 10 cameras; it is true that I was also influenced by a setup of another big O.B. Van with up to 20 cameras
• the contact closure of all GPI inputs shall require no external power supply in order to simply do their job
• the actual configuration of the operating parameters shall not depend on a unique method or some particular operating system; instead it must be able to be carried out, as much as possible, with what might be at hand to the technical staff at any given moment (well, within reasonable limits)
• the communication with the router shall be directly network-based; no intermediate PC shall be required, once the configuration has been set
• a nice looking alphanumeric LCD display shall complete the front panel design; its purpose shall be just informative, so that a few basic informations – like an IP or a MAC address – be easy to find out
• all internal pre-built subassemblies shall be EMC compliant certified; additionally, my own custom internal circuits shall be specifically designed by taking this criterion into account, so the resulting product shall fall within the EMC boundaries for a Class A product (= commercial and industrial usage)
• all components and constructive parts shall be RoHS compliant certified, so that the resulting product will be also RoHS compliant
• the name of the interface shall be JOyVerride :)

Three months later the idea materialized in a true professional equipment, on par with other products in the same industry.

Because this has become a commercial project, it is now hosted on its own web page:

  JOyVerride - Joystick Override GPI Input Interface