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Meter gateway. A new approach for energy monitoring

posted May 14, 2013, 2:48 AM by Daniel Berenguer   [ updated May 14, 2013, 5:04 AM ]
We have gotten a good experience from the meter-board project. We have learned about the potential of measuring energy consumptions from a DIY perspective and how each application may differ from the other. Meter-board is called to become one of our most popular reference designs, a very cheap way to read up to seven power circuits from a single panStamp. And we are not talking about simply reading RMS current values but complete readings about active and apparent power, power factor and RMS currents and voltage. However we have finally decided to not to produce these boards in a regular basis. Our reasons may be summarized here:

  • Atmel AVR's ADC's are probably not the most suitable converters for this kind of applications.
  • Meter-boards needs to be calibrated for each new voltage or current transformer.
  • Meter-board can only read single-phase circuits. Users interested in reading 3-phase lines had to search elsewhere.
  • Selling this board implies maintaining a stock of current transformers at different currents. Then we had to source voltage transformers for different voltages and frequencies too.
  • Again, we hit against the usual certification issues. Even if we were using voltage and current transformers, the risk of electric hazard is always there, specially when these devices have to be mounted into an electric box.
  • And finally, we don't want to become a supplier of sub-metering products. We believe that doing this would require us to allocate an important part of our time and resources.
As result, we have a nice reference design but we need to take a very different approach. The question is: why re-inventing the wheel? There are tons of power meter devices in the market, each one for its own specific use. We have single-phase meters for sub-metering applications, we have all those utility meters, three-phase devices, bi-directional managers, expensive professional devices, cheap DIN-rail meters, certified products for each market, etc, etc. And you know what?, a good amount of these products already provide a serial interface. This is the case of all the families of Modbus meters, RS485 proprietary devices and other serial solutions based on RS232 or opto-isolated TTL.. Thus, why not taking the readings from existing power meters?

After concluding the above, we put our tired minds to work. Some hours after that got a new design, our new RS485 gateway:

RS485 gateway for panStamp
Figure 1 : RS485 gateway for panStamp

The potential for this device is huge: a cheap wireless gateway capable to read energy meters from many companies, metering or submetering, single-phase or 3-phase, The available enclosure would let us mount the gateway on a DIN-rail or on the wall, close to the power meter.

RS485 gateway with cover

Figure 2 : RS485 gateway with cover

As a starting point, we will develop a SWAP-enabled application for Modbus-compatible meters. We have even ordered some of these cheap (Modbus) power meters from aliexpress (take a look at those prices!).

Maker Faire will be a good place where to validate the concept. We expect to get comments and fresh ideas from visitors and makers before diving into a new promising development adventure. Remember, we will be at booth 408, Startup area in the Expo Hall next weekend in the greatest Maker Faire event in the world. Can't wait!!