Perhaps a reed switch/Hall effect sensor and a permanent magnet? Allows for versatility in mounting position, largely immune to weather, and very simple to operate. What are the consequences of failure? Personal injury? On Mon, Sep 23, 2013 at 1:48 AM, James Cameron wrote: > G'day, > > A friend has asked for a way to announce the opening of a farm gate. > > I can handle the announcing, but the detection seems to have ample > opportunities for error. > > The gate consists of two frames with mesh, made of galvanised steel, > with a chain joining them in the centre. The frames are each attached > by hinges to a vertical wooden post. The frames can open either > inward or outward. The gate is normally closed, and is opened several > times a day. > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .