If you are looking for an all-in-one device for monitoring your home energy needs, a low-cost single board computer such as the RBPi or Raspberry Pi along with an add-on shield is all you need. The emonPi board is a low-cost shield that is bereft of any enclosure, HDD and LCD.

However, when connected with an LCD for status display, hard-drive for local logging and backup and a web-connected RBPi, the emonPi makes a high-quality and robust unit. Enclose it in a suitable enclosure and you have a stand-alone energy monitoring station.

The design of the emonPi allows it to be a perfect fit for those who install heat-pump monitoring systems. Usually, these systems require several temperature sensors that must also be wired up along with power monitoring. Accompanying modules offer a myriad of options.
For example, the emonPi can also act as an emonBase, as it has options for rad
io (RFM12B/RFM69CW) to receive data from other wireless nodes. These nodes include emonTH, for measuring room temperature and humidity. Another energy-monitoring node, the emonTX V3 can send the current time to the LCD, emonGLCD.

The status LCD makes it easy to install, setup and debug the emonPi system as an energy monitor sensing mode and an all-in-one remote posting base station. This makes the emonPi a great tool for remote administration, since, with a proper networking configuration the RBPi can be accessed remotely. Thus, you may check its log files and even upload firmware onto the ATmega328 of the emonPi.

The emonPi monitors energy through a two-channel CT or current transformer along with an AC sample input. It can power up the RBPi and an external hard disk drive without using an external USB hub. Additionally, the emonPi can function even without a hard disk drive being connected to it.

The RJ45 breakout board makes it very easy to attach several temperature sensors to the RJ45 on-wire temperature bus provided by a DS18B20. This is eminently suitable for multi-sensor setups such as in heat pump monitoring applications. The RJ45 also has IRW and PWM I/Os.

The emonPi is compatible to all models of the RBPi and its options for RFM21B and RFM69CW along with an SMA antenna makes it capable of receiving or transmitting data from other sensor nodes. One can control remote plugs with the OOK or On-Off keying transmitter.

All hardware, firmware and software are open-source and the ATmega328 on the emonPi can remotely upload sketches via the serial port of the RBPi. However, compared to the emonTX V3, emonPi has some disadvantages.

The emonPi module is not capable of making measurements on three-phase systems as there is only one CT monitoring two channels. As the RBPi has high power requirements, it is not possible to power the emonPi from batteries. You cannot also use an AC-AC adapter, because, for measuring real power, you must use both a 5VDC and a 9VAC adapter. Remote location of the utility meter requires Ethernet connection or Wi-Fi connectivity. Additionally, the emonPi requires a larger enclosure as compared to what an emonTX V3 uses.