switching problem

Bill Wright · 2009-09-07T19:17:17+00:00

The cupboard has two doors, which open independently. The plan is to fit two push switches of the type sold for this purpose, one for each door. The switches will control a light that will shine into the cupboard, which is rather deep and gloomy. These switches are 'on' when the plunger is out, so the light comes on when the door is open. I also intend to use a timer so that if the door or doors are left open the light will eventually go out. The timer will commence timing when the supply is applied (the door(s) are opened) and if the door or doors are left open the light will eventually go out. If the doors are closed during the timing period the light will go out immediately. In order to initiate a timing period and turn the light on the door must be closed, then the timing period starts when the door opens. I've sorted the timer out. It's a multifunction one, and it does what I want. But ideally I'd like the light to come on if either or both doors are opened, and stay on for the full duration of the timing period even if one of the two doors is shut. With one door it's simple. The one switch controls the timer perfectly. But with two doors and two switches the best I've done is to have the switches in series, so that both doors have to be open to initiate the timing period. With the switches in parallel, if one door has been left open the timing period will not commence when the other door is opened. It is necesssary for both doors to be closed, then either to be opened. If the switches are in series, for the timing period to start one or both doors must be shut, then both must be open.Suggestions anyone?Bill

switching problem

Sep 07, 2009 40 Replies

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I think the problem is the switches.

If you can get a switch on each door which makes a *momentary* contact as the door is opened, but is otherwise open, you can wire them in parallel. They used to be sold for shop door-bells. In effect what you want is the reverse of a a SPDT switch with centre off, ie with a centre-on action midway between door open and door closed.

Could you do something with two reed switches per door, the magnets arranged so with operating distances so that when both switches are made (door closed) or both switches are open (door open) the circuit is open-circuit, but there's a gap in the middle when one switch is made and the other isn't that gives you a closed-circuit and a trigger pulse.

Owain