For our home monitoring system I have long had a problem -

- We do measure the amount of electricity we use, and plot/graph this quite accurately

- We do use gas for heating (2 boilers) plus a hob in the kitchen.

Measuring usage of gas seems to be difficult with any easily accessible technology, and the very oldfashioned meter we have for the house will not work with any of the methods I have seen so far - as we do not have either a flashing led nor a rotating disc.

So while trying to think through this I came to the following conclusion :

- The gas usage for the hob is probably little compared to the boilers, and there is very little we can do to reduce it, therefore I will concentrate on the usage by the boilers.

The boiler usage is "digital" - it is either on or off. Once a year we have a engineer around to service the boilers, and as part of the service he gives us a report that tells us how much gas each boiler consumes per minute.

Therefore the gas usage is possible to infer from the time each boiler is turned on.

When the boiler turn on you can observe this as the pilotlight turns on the full gas fire inside the boiler, and this can be observed through the observation "hole".

So I have added a LDR to a Jeeduino, bluetacked it to the pilot light "hole" to see if I can accurately measure the difference in light levels between only the pilot light being on, and the full gas flame.