Dumb Meters… they have hearts too!

For the past year and a half I have habitually been recording my Gas and Electricity meter readings (my wife would probably say it was an obsession!). Each week I would clamber under the stairs armed with my iPhone flashlight, crawling through the dust I would read the digits from my old ‘dumb’ meters. I would then send the readings off to British Gas via their iPhone app, also storing them in another iPhone app called ‘Meter Readings‘.

As much as I enjoyed crawling under the stairs, I kept thinking that there must be a better way (aside from getting smart meters). After a quick Google I came across a group of people at openenergymonitor.org, a project which its aim is to develop open-source energy monitoring tools. After reading a number of articles on their site I found out that I may be able to calculate my energy usage by measuring my meters ‘pulse’.

Stethoscopes at the ready?

Not too dissimilar to our own bodies it turns out that, in some shape or form, nearly all Gas and Electricity meters have a ‘pulse’. Depending on the meter model this ‘pulse’ may be electrical or mechanical but, with the right sensor, we can count these pulses:

Electrical pulses:

  • LED’s – Can be measured easily using a light sensor (e.g LDR), these are usually viable but in some cases the LED may be infra-red.
  • Serial – Some meters have an electrical serial interface, this may be an RJ11 port which pulses high / low and may be able to be connected directly to a computer.

Mechanical pulses:

  • Spinning disk – Some older Electricity meters have a disk which rotates. Usually this disk has a black line or stripe on it which, with a reflective sensor, you can count each rotation with.
  • Rotary digits (magnetic) – Other meters have rotating digits, a series of small cylinders with numbers 0-9. In some cases the manufacturer places a small magnet behind the ‘0’ of the least significant rotating digit which, if a magnetic sensor (e.g reed switch) is placed in the correct position, you can count each rotation with.
  • Rotary digits (reflective) – The same as above, only this time the manufacturer may place a small reflective object (mirror) on the ‘0’ of the least significant rotating digit which, with a a photo reflective sensor, you can count each rotation with.

No matter which of the above your meter has, each ‘pulse’ (rotation, blink etc) represents a unit of energy used, which, with a simple bit of simple maths, you can work out rate and consumption figures. The amount of energy per pulse may be printed on the front of the meter.

Old Electricity Meter
Old Electricity Meter

My Electricity Meter

My Electricity Meter was a GEC (General Electric Company) C11B2A-H, a very chunky beast! This meter has a spinning disk which spins at ‘200 rev/kWh’. There are also some rotary digits, but I don’t think there is a magnet or mirror placed in these.

The rotating disk has a small black stripe on its edge, so I opted to count the disk rotations using a photo-reflective sensor and calculate energy usage.


Old Gas Meter
Old Gas Meter

My Gas Meter

My gas meter was a Parkinson Cowan (Thorn EMI) diaphragm meter. This meter has a set of rotating digits, as well as a little spinning red hand (like a clock).

Unfortunately I was unable to detect the presence of a magnet in the least significant digit (using a compass), nor was there a reflective digit.

My only hope was the spinning clock hand which spins once for every ft3 (cubic feet) of Gas used. I thought that I may, with the right sensor, be able to detect it passing 12 O’clock, but this was harder than I thought.


* As an aside I have also heard of some projects which use a webcam and OCR (Optical Character Recognition) software to read the meter readings, but this may be a bit beyond my capabilities.

In my next post I go on to explain in more detail how I used an Arduino to measure my Electricity usage.

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