In a PM., @praveen_kumar reported that he is deeply confused. His initial request was to transfer the data serially from an Arduino to a Raspberry Pi.
The emonPi, as sold in the OEM Shop, is a cut-down emonTx and a Raspberry Pi inside the same box, with an LCD and pushbutton added, and the Raspberry Pi also has an RFM69Pi module to allow it to transmit to an emonGLCD and receive from several emonTHs or emonTx’s. The emonTx sends its data to the RPi’s GPIO port serially.
Therefore, the easiest way to achieve what you want is to replicate the parts of the emonPi that are important to you. Those are the cut-down emonTx (which is what your Arduino is doing) and the RPi.
Interconnections:
I shall not tell you what to connect, I will tell you how to find out for yourself. That way, you will know for next time.
Get the emonPi schematic diagram from Resources. Find the RXD and TXD lines from the AtMega processor and find the same labels on the RPi GPIO. You’ll need to find the RXD and TXD on your Arduino. You can connect the TXD from the RPi directly to your Arduino, but you MUST add a voltage divider in the TXD line coming from your Arduino to reduce the voltage from 5 V to 3.3 V. The same is necessary on your emonTx Shield to reduce the voltage for the RFM69Pi, so copy what is done there. Connect to the same GPIO pins on your RPi. You’ll also need to connect the two GNDs together. That’s all you need.
Firmware - RPi:
Buy an 8GB SD card, and download the latest emoncms image. Follow the instructions in the emonPi firmware guide in Resources.
Arduino Sketch:
You need to change your Arduino sketch to send data via the serial port in the format that emonHub expects. This thread gives the format: Emonhub interfacer for 'new' emontx serial format - #2 by glyn.hudson
You must not send anything else at all via the serial port.
EmonHub:
In the configuration, you will need to set up an interfacer as described in that same thread and in the GIthub readme that’s linked from it.
In emonHub, you can also send your data to emoncms.org, as well as, or instead of, to the emoncms running on your RPi.