Monitoring gas usage

Through the years I’ve used various methods to monitor our gas usage.


By counting how many times the dial rotates, it is possible to monitor gas usage with a resolution of 0.01 cubic meters (= 10 dm3, 10 liter). Sensing the rotation of the last digit on the gas meter is done with a CNY70, a reflective optical sensor. This CNY70 has a light source that emits an IR beam and it has a detector in the same housing as the emitter, that will detect the reflection on the mirror of the digit “6”. Here you see the CNY70 in front of the rightmost counter, where the digit “6” has a mirror.

The detector side of the CNY70 is connected to a LM741 opamp to amplify the signal, resulting in a nice pulse signal when the mirror passes the CNY70.

pcs10(Yellow is the CNY70 output, Green is the LM741 output). This pulse signal is being fed to a Dallas 1-Wire DS2423-based counter from Hobbyboards.The DS2423 is being polled by my Home Automation software, that collects the counter value at regular intervals and stores the counter values to a SQL database.


The CNY70 was replaced by one that comes from RFXCOM, complete with cable and jack plug. Here you see the sensor in front of the “6”. The sensor is connected to an RFXPulse module. This module takes care of identifying the pulses. The RFXPulse module is inserted into a RFXMeter, which takes care of the counting and transmitting the counter value. As you can see my RFXMeter contains 3 RFXPulse modules: for Gas, Water and Power.

The RF signals from the RFXMeter are received by a RFXCOM receiver. This receiver then transmits the data over my LAN to my Home Automation system. There the data packets are decoded, the counter values are calculated and stored in a SQL Server table on a regular basis.

Gas usage is stored on a hourly basis, meaning that for every hour that gas has been used in our house, there is a record (row) in the table that holds the data for that gas usage.With this it is possible to create very detailed charts of the gas usage.

Smart meter

All this is not necessary anymore, because we have a smart meter since September 2012 that makes all these things obsolete; every hour it reports the gas usage on its so-called P1 port, which makes life very easy. More about the smart meter here.

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