For a while now I have been working on developing a Raspberry Pi energy monitoring shield. Here is a preview of the first prototype design.

The emonPi is not designed to totally replace the emonTx V3, but rather to complement it. I see the emonPi fulfilling two applications:

1. As a low cost Raspberry Pi add-on shield to make all-in-one home energy monitoring unit based on the Raspberry Pi.  We will produce a version of the emonPi board on it's own (without enclosure, HDD and LCD), maybe even with just SMT components ready assembled (like the Arduino Lenoardo) to being the cost down further.

2. As a high quality, robust and nicely enclosed stand-alone energy monitoring unit and web-connected base station with LCD status display, built in hard-drive for local logging and backup. The emonPi has also been designed to be perfect for installers of heat-pump monitoring systems which require many temperature sensor wired up (see temperature sensing part of my forum post update) as well as power monitoring.

The emonPi has got an option for RFM12B / RFM69CW radio to enable it also to act as an emonBase, receiving date from other wireless nodes such as emonTH (room temperature and humidity node), emonTx V3 (energy monitoring node) and transmitting the current time to the emonGLCD LCD display. 

Since the emonPi is an energy monitor sensing node and remote posting base station all-in-one and coupled with a status LCD this should make system setup, installation and debugging easier. The emonPi should also be great for remote administration since with the correct network config the Raspberry Pi can be accessed remotely, log files checked and even upload Arduino sketch firmware onto the emonPi's ATmega328.

Development has been documented in an ongoing open forum thread: http://openenergymonitor.org/emon/node/3937

My latest update post can be viewed here: http://openenergymonitor.org/emon/node/3937#comment-21865

emon Pi Features 

• • Two channel CT monitoring with AC sample input 

  • Ability to power the Raspberry Pi and an external HDD without the need for an additional USB hub, emonPi can also function without a HDD

  • RJ45 DS18B20 on-wire temperature bus to allow many temperature sensors to easily be added using a RJ45 breakout board for heatpump monitoring applications 

  • PWM and IRW I/O's on RJ45 

  • Status LCD

  • Compatible with RaspberryPi model A and model B 

  • Option for RFM12B / RFM69CW with SMA antenna to receive or transmit data from other sensor nodes

  • OOK (on-off keying) transmitter footprint for controlling remote plugs etc. 

  • ATmega328 with ability to remotely upload sketches vis Raspberry Pi Serial 

  • Open-source hardware, firmware and software 

  • High quality custom made, wall mountable enclosure

   End-plate silkscreen draft:

See G+ album for more photos:https://plus.google.com/b/114424977493521882459/photos/+OpenenergymonitorOrgpage/albums/5999656723837107313

 LCD demo:

Please join in the emonPi's open-development forum thread if you have any ideas of thoughts to contribute:

http://openenergymonitor.org/emon/node/3937#comment-21865

The disadvantages of the emonPi compared to the current emonTx V3 are:

• • Only two CT channels, no (approximate) 3-phase

  • Due to higher power requirements of the Pi, the emonPi can't be powered from batteries, 5V DC USB mini-B is required. 

  • Again, due to higher power requirements of the Pi, the emonPi can't be powered from an AC-AC adapter, for real power a 5V DC and 9V AC adapter will both be required. 

  • Requires wifi connectivity or Ethernet to reach the location where the utility meter is located

  • Larger enclosure than the emonTx V3