Homebrew do you need a pi?

Hi, new user here.

I was brought here after seeing the cost of the Smappee & Sense monitors only to see the price of an emonPi setup is pretty much the same, if not more. So I have of course now started looking at the DIY option.

I have read through most of the pages on learn.openenergymonitor.org now and using an arduino and sensors I should be able to get most of what I want or live energy monitoring. I dont need solar or temp monitoring etc, and this is all very low cost. So I’m confused as to where the Pi comes in on the EmonPi, do you really need a Pi? If it’s just for posting data via a network connection can you not use an ESP8266 based arduino?

Also, and I’m not bashing the price of the EmonPi as I’m sure its justified, but compared to an Arduino, Pi, and sensors it does seem pricey. What does the EmonPi PCB give you that that the home brewer cant do?


A nice box to start with, the knowledge that it will work, plus of course a part of the cost goes to supporting the development work that went into creating it and emonCMS, and making all the information and expertise available to you via this website. (There’s no such thing as a free lunch, and we DON’T sell your data.)

I fully apreciate the cost goes towards the effort behind the project, and if I go ahead I would buy my sensors through this shop to help support it that way. But, with any ‘open’ project you have to expect and in fact invite the hombrew and diy community.

I have some arduino’s laying around already and even some pi’s, I have a 3D printer and can design my own box, but thats all irrelevant. I really did mean what is the Pi for, nothing in the the learn documents explains where the pi comes in and what it does. I also did mean the emonPi PCB even though you crossed it out because this is one of the purchase options in the shope ‘PCB Only’.

The “Guide” or “Resources” is probably where you should have been looking. “Learn” is biased more towards the theoretical background knowledge.

The emonPi you can buy is a cut down emonTx and a Raspberry Pi (plus a display) in a box.
The emonTx part does the energy monitoring (including things you say don’t want like temperature and pulse input and possibly the RFM69 radio), the RPi hosts emonCMS which gives you the database to store the data and the web pages to display it.

An emonBase is a RPi plus the radio receiver (or an emonPi minus the energy monitoring).

Ahh I think I understand now. I thought emonCMS was cloud hosted at the emonPi posted its data out to it, I didnt realise the cms was actually hosted locally on the pi, that makes sense now thank you.

It can be either or both. However, there’s now a charge to use the emoncms.org hosted version - details here: Emoncms.org billing

Note, the two versions are very close relatives, but there are some differences.