The door to success

Doors were once made of sturdy wood to control access, controlled by constructions of steel and brass, actuated by metal keys. Now the growing trend, particularly with hotel rooms, is to have electronically controlled and electrically actuated mechanisms. Callers are no longer expected to make their presence known by percussive action on the door surface or knocker, but by pressing a bell push. And those beyond the door increasingly want to be able to see who is on the other side, without revealing whether they are present or not, before releasing the locking mechanism. All these facilities require electricity, either delivered by wires – which may not be very effective in the event of a power cut – or by batteries, which users very often forget to replace until they stop working. Solar panels could provide an alternative power source, but would be unlikely to work in the dark, unless associated with secondary batteries. And small nuclear power sources, as used in military satellites, are unlikely to be cost effective. The Challenge Since doors have to be opened and shut, our challenge is to come up with the best means to use the door's action of opening and closing – or even perhaps the act of turning the handle – to provide the power. Since the most power is available when the door is opened or closed, and required when it is shut and stationary, it might also be wise to come up with some storage mechanism – unless the door is going to be powered by energy generated by using a knocker. There are many solutions to this problem. One offered below solves the problem in some style and at very low cost – without recourse to any kind of electronics. There are also many other technologies that could be used. The problem, in this instance, is not so much about solving the dilemma itself, as much as it is to decide on the most cost-effective and practicable means to do so. For those without access to the web, one or more solutions will be described in our March edition. If you can find an even better way to meet the challenge, please let us know. Solution One possible solution has been demonstrated by four Hong Kong teenagers, Ho Wai-tat, Man Chun-wai, Lau Sui-lun and Yiu Kwun-cheun. Their concept, which won them first prize at a School Science Exhibition in Hong Kong – is called 'Electdoor', a gear-driven device that can store the energy produced by each swing of the door. Speaking to the Indian newspaper Design News and Analysis, Man said that "We reckon that, on an average, everyone in Hong Kong opens or closes a door some 20 times a day. If all that mechanical energy expended by Hong Kong's 7 million population could be tapped by Electdoor, it would save the power equivalent of some 365,000 batteries a year". Hong Kong's Environment Secretary, Edward Yau Tang-wah said that he would have government engineers examine the practicability of installing the device in government departments. But this is far from the only means by which the problem of powering door gadgets can be solved. Piezoelectric devices might be considered, and how about resurrecting old fashioned bell pulls, with the wires attached not to a mechanical bell in the servant's quarters as of old, but to a small electric generator to power a sounder or if the person at the door has a suitable keying chip, to power the lock? Clever solutions, which meet the goal with the least expenditure, should expect to find a ready market.