Washing line tension

It seems to me likely that as washing on a washing line dries, the tension on the line should reduce as the mass of the clothing on the line will be less. It may be possible for a sensor and processor to monitor the tension of the line, and hence infer when the washing is likely to be dry - the decrease in tension will have levelled off.

The line tension sensor may also be able to warn when it is raining, as the clothes will begin to increase in mass (although an integrated rain gauge or other weather sensors would probably be more accurate.

However, such an approach may be limited by the level of noise in the system due to wind causing fluctuations in tension of the line. Other methods could be: photo-spectroscopic analysis of a laser pointed as a particular (and hopefully representative) item of clothing; humidity sensor placed along the line.