One of the larger goals for this project is to build an ultra low power platform to measure a variety of sensors. The next logical step after water meters is measuring gas meters for a few reasons. There are no passive devices on the market that do this for 'dumb' mechanical meters as far as I know. Second, natural gas companies usually charge months after a home owners usage (similar to water), which can lead to surprise bills. However, gas meters work a bit differently than water meters, which presents new challenges.

Source: Wikipedia

Basic mechanical gas meters use a diaphragm that expands and contracts with the flow of gas. This in turn moves levers and gears to eventually turn a mechanical dial indicating the usage. There are no magnets in this design so I decided to measure the change in the earth's magnetic field caused by the moving metallic parts instead.

In the previous two post I discussed how the earth's magnetic field was adding a variable DC offset depending on the orientation of the sensor. In this case, I'm using it to my advantage. I'll do a more detailed write up on how I modified the design to do this in the next post. For now, check out the video demo above.