Computers: Feedback: Mouse tales

Rupert Goodwins writes: Regarding the story of 'The Mouse that Dies in Sunlight' (5 November), most mice I know have their infra-red gubbins shielded by adequate thicknesses of opaque plastic.

The only time I have had problems with sunlight and motion sensors was when I was debugging a Spectrum disk drive interface.

The bare drives would stop working after about 3pm. We traced this to Father Sol's warming rays glancing through the Brentwood windows at an oblique angle, rather than - as first suspected - Bacchus's lunchtime intake befuddling the oblique minds of the hardware designers.

The disk drives, when first turned on, attempted to locate their heads by moving them to the end of their travel, at which point a small lug of plastic interrupted an infra-red light beam. The interfering photons from the sunlight streaming in the window imitated those from the infra-red beam to such an extent that the drive could not tell when it had moved its heads to the end of the road - it would then attempt to move them further still, to loud noises and eventual smoke.

This problem was diagnosed by sticking small flags to the top of the heads with Blu-Tack and observing the behaviour of the system with window blinds alternately open and closed. It was cured by small flaps of cardboard - a traditional way to sort one's head out - glued to the drive assembly. But I am amazed that a mouse, let alone a large number of same, would suffer from this problem.

To be fair, it could be that some Far Eastern silicon foundry has started churning out particularly poor optoreceptors which are particularly sensitive to stray radiaton, but I cannot off-hand see how.

I would suspect that the poor sleek tim'rous beasties were just getting too warm.

Andrew Brown adds: An altogether sadder tale involving mice reaches us from a friend of the page, who wishes in the current climate of animal rights activism to remain anonymous.

She had left her son engrossed in front of the Microsoft Dinosaurs CD-rom, which he found so fascinating that he had brought down his beloved pet mouse to watch it too from a little nest on the chair beside him. Then he got stuck in the program and called his mother to help.

She rushed in from the kitchen and plumped herself down in front of the keyboard to fix it . . . Neither of them noticed what had happened until she stood up again.