The notorious Mr Babbage (part one)

The eponymous hero of this blog is the affectionate name given to the hardware behind the big scoreboard of Family Fortunes. As I’ve been threatening to discuss this at some length, what better way to start this blog off than by doing just that?

For the ‘classic’ era, three entirely separate pieces of hardware have done the job. (I’m avoiding the most recent ‘All Star version which is just a traditional screen, as the older ones are far more interesting). For this, let’s do some detective work (with just a little bit of engineering thrown in)…

Mr Babbage I – from BOB to MAX

If we look at a standard opening for a Bob Monkhouse era Family Fortunes, we can see that for a single colour display, it’s certainly capable of a few fancy effects (the twinkling stars for one).


The computer system needed stores the necessary data needed to display, for the studio team to operate as necessary. At the time, the easiest way to do this for this type of system would be to have a large grid of lights controllable from some central system, and some digging suggests that the English Electric Valve Company did indeed make something capable of that at the time, but not that would be capable of handling the sheer number of elements required at once. The solution is one that is surprisingly simple, and still regularly in use in many contexts, such as the average slot machine.

Within each individual ‘character’ of the display, there are 35 individual lights, arranged as a 7×5 rectangle (i.e. 7 rows with 5 columns). In an ideal world all of these would be connected individually to our central system, but this would rapidly become impractical. In order for such a device to be workable, the designer must reduce the number of connections as much as is possible, while still providing a coherent display.

Matrix 1
As shown, both row and column are needed to activate a light, but the effect is to greatly simplify the connections

Looking at an individual character, the individual lights are connected to one another such that all lights on a given row, and all lights on a given column are connected together. To illuminate a light, the row and column connections must both be activated. This simple act on its own has already reduced the 35 specific connections we need for each character down to 12 (7+5), but this means that directly driving the full display at once is now totally impossible. The thing is, we don’t need to.

Light Multiplexing

The trick to achieving a usable display is to rely on the physics associated with this type of light, namely that a light will not go out immediately as the power is removed. Taking our individual character example again, let’s consider the effect of rapidly scanning through the required lights, one column at a time. (For clarity, this selection process has been significantly slowed down, in reality this whole process would take tenths of a second)

turkeymux
By synchronizing the row power with the rapidly changing column, an image can be built up by not letting the lamps go out entirely.

By the time we return to the beginning and the light is about to dim, the power is restored, as is the brightness. It should be pointed out that there’s no specific reason for doing this by column, working by row is equally effective. However, in this case, Mr Babbage appears to be set up to run column by column, addressing multiple characters at once, so that’s the example we use here.

In the concluding Part 2, we go right up to the days of All Star Family Fortunes, via Ice hockey arenas and magnetism. And if that doesn’t have you keen, I don’t know what will.

Advertisements

One thought on “The notorious Mr Babbage (part one)

Leave a Reply

Please log in using one of these methods to post your comment:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.