Here is some evolution about the Gas Meter 'Gazpar' for which I developped a generic battery backed-up solution.
As mentionned before, the "official" cable is for sale at a hefty price (for what it is) of ~20€. I would have gone for this cable, had the meter been outdoors or in a humid room, but since it is located in my kitchen, I simply used the trick found on some forums: Female dupont wires. And it works very well indeed.
One of the main differences between the electricity and gas smart meters, is that the former will deliver all the information (including current reading) in a continuous way. In case of power cut, upgrade or crash of the microcomputer/microcontroller, nothing is really lost and things will restart as soon as possible.
The gas meter, smart or not, will only give pulses... if nobody is listening, the information is lost and the status of the reading not longer accurate.
Keeping the value
The basic idea is to decouple the counting process from the processing unit. The counting unit should not need any update or needs to restart often.
One idea was to write the current value on a flash memory but these are notoriously bad as time goes by. Wear and tear could soon be an issue.
Apprently, there is a kind of memory called Ferroelectric RAM/FRAM for which the number of write cycle is not a problem. But these are not wildly sold (but can be found as breakout board) and certainly overkill for just keeping a counter.
So in the end, the easiest solution seemed to use a basic ATTiny85 powered and keeping the value in RAM. This solution will be described in the next post.