Run a Raspberry Pi and USB hub off one power brick

Annoyed by having to take up so many power plug spaces for supposedly low power devices? 

What's going on here?

• Raspberry Pi needs minimum 700mA 
• Power goes into USB hub (2A 5V DC) 
• Hub provides Pi with power via micro-USB (white)
• Pi's USB connects to hub for devices 
• It works, trust me :) just don't use lots of USB devices that need power. 

Ignore the bit at the bottom with the ribbon cable; it's a Nordic radio attached to the GPIO pins for a wireless node project. 

This whole thing is then hung on the wall. Blu-tak holds the hub on the front, and the enclosure has slots on the back to slide it onto screw heads. After a while the hub very slowly slides down and then hangs from the cable; I think I'll have to add tape.

Solar power monitoring on Raspberry Pi/Linux

I've had solar panels installed since 2012 after my wife and I bought our first home. I have always been interested in monitoring our power usage as well as solar power production and trying to optimise/minimise use. It was relatively easy to get data from our Power-One Aurora 2kW photovoltaic inverter, and upload that via a Raspberry Pi (v2) to PVoutput.org.

A full day's live output after it was working again

This worked fairly well with only minor hiccups from mid-2014 through to early 2016 when the Pi started having regular issues, and eventually stopped booting altogether in August. The SD card basically just wore out, I used ddrescue to recover it with < 100 kB missing but apparently those were important bytes. I have finally gotten around to recovering it, having to reverse engineer my own setup, so I am documenting it here. I will also cover how to make it more resilient.

I stalled on monitoring the power usage for the house, but recently discovered some progress in this area, which can be a whole other post.

You will need

This guide is for my setup as follows, yours may differ:

• Aurora PV inverters with either
• an internal RS485 serial port connection (may void warranty? do your own research) 
• an external USB port (larger models, probably indoor only) - though I have not used one
• Relevant hardware to connect
• in my case I used a long Cat 5 ethernet cable to carry the signals from the inverter
• an RS485 to USB adapter
• Raspberry Pi or other Linux-based host you're going to connect it to, ideally low power
• With an 8GB+ SD card, a good one, not no-name brand
• Ideally one that does wear-leveling, but I was unable to find any reliable info
• With Raspbian with desktop installed, configured and updated
• You aren't afraid to install packages and compile things
• Posting data to PVoutput.org or wherever, but this part is all software and much easier, plus my setup also logs locally. 

If you wanted to use a Windows host, there are actually more software options for Aurora inverters such as PVBeanCounter, but I don't want to run anything 24/7 that runs Windows.

Caveats

• The ONLY ready-to-go software I could find which supported Aurora, ran on Linux, and posted to PVoutput.org is called Aurora Monitor which:
• hasn't been updated in years, but seems rock-solid anyway
• is open source (GPLv3)
• requires a desktop! Although all I wanted was to log the data, it has a GUI, so I have to run the desktop which makes this a little more complicated and inefficient :( 
• however you don't need to connect a monitor permanently 
• also logs its data to disk, at a rate of about 350 kB per day, so make sure you have spare space or setup log rotation. 
• The above means you need a desktop Linux distro, I used Raspbian
• ... and the current Raspbian with Desktop is 4.7GB so you need an 8GB SD card
• Don't put the Pi anywhere that's hard to get to as you may occasionally need to reboot it or repair the SD card
• RS485 (multidrop serial) is not the same as regular RS232 (single) serial. You DO need the right USB device, which basically converts it to RS232. On the plus side, if you have multiple inverters, you can daisy chain them on the same line, but I think the unit I have only supports one connection. 
• Mine is an FTDI idVendor=0403, idProduct=6001 "FT232R USB UART" 
• The first one I bought was the cheapest possible and didn't last long, get FTDI

Steps

Read all these instructions before you start to make sure you aren't missing or misunderstanding anything!

Connect cable to RS485 USB adapter

Here's a stock photo of the same type of adapter I have, for example search ebay for "USB To TTL RS485 Serial Adapter FTDI FT232RL". It simply has screw terminals for the wires. Keep track of which is which for Rx/Tx.

For more photos of my setup look further down.

Connect to PV Inverter

WARNINGS!

• You must have an electrician do this! 
• This may void your warranty! 
• Follow the manufacturer's instructions to turn off ALL power to the inverter at the meter box and then PV array! 
• Make sure any entrances to the device are sealed up waterproof and insect-proof!
• Leave the other end of the cable disconnected from anything and with no wires touching while you do this end! 
• Do your own research! Don't blame me if any of this breaks or costs you money!
• If you don't understand exactly what this is about and what all this means, just stop now! 

This photo shows the screw-terminals for the serial connection. 

1. Run an appropriately weather shielded cable with enough wires from wherever your Pi is going to live, in through the holes in the bottom (replace or retrofit the hole cover as needed)
2. Ensure it has proper strain relief (simple way: tie a loose knot around a small non-conductive object) so it won't pull out and has enough wire to easily reach, but not fill up the unit
3. Wire them up, ensure any spare wires are cut off and won't touch anything
4. The terminator switch is used for multidrop cables, should be enabled only on the last unit. I think it wasn't changed. 
5. Close up the box
6. Power on the unit following correct process (power off in reverse) 
7. Connect up the other end to your RS486 to USB adapter and ensure it works (may have to fiddle around with rx vs tx, etc) - exercise left up to reader
8. Power off again
9. Waterproof the cable entrance
10. Power back on

Compiling Aurora Monitor

These assume you are familiar with Raspberry Pi, Linux (Raspbian), and have that set up already.

1. Download Aurora Monitor to the Pi and unzip it 
2. It has binaries for 32 bit and 64 bit but you need to compile it for ARM
1. run "sudo apt-get install build-essential libwxgtk2.8-0 libwxgtk2.8-dev"
2. run "cd /src"
3. run "make"
4. wait about 15 minutes (no, really)
5. "auroramon" binary is built, you can move it wherever you want
3. Run desktop if you haven't already
4. Run auroramon and ensure it works, but of course it won't have data.

Set up software

This part can only be done when the sun is out and the unit is producing power.

For more help and screenshots see http://auroramonitor.sourceforge.net/ but here is a quick rundown:

1. Plug in your USB adapter and configure the program:
1. Serial port to use (check "ls /dev/tty*" it's probably ttyUSB0 if there's only one) 
2. Location (lat/long) for automatic adjustment to sunrise/sunset and azimuth
3. Solar panel direction and angle if known (I don't)
4. Etc etc 
2. Click Inverter Status in the menu to ensure it's connected, you should also see some numbers in the boxes at the bottom 
3. After a few minutes there should be some data points on the chart! 
4. Uploading to PVoutput.org: get a free account and go to Account Settings to get your API key
5. Wait a few minutes to see your live data appear on your chart online! 

Resiliency

• Ensure the desktop starts on boot: run "sudo raspi-config" and go through the menus
• Make auroramonitor start with the desktop: https://raspberrypi.stackexchange.com/a/45554/4226
• For the SD card: optionally, reduce the root partition size a bit to leave room for remapped bad sectors (not sure if this will actually work); I left 256 MB at the end, using GParted on my PC 

After 3 years my USB adapter was getting a bit dusty, so to protect it from dust, insects or damage I put it in a plastic enclosure:

See my awesome screw-terminal wire protection?

Classy container

Due to the frosted plastic it has a cool glow!

Potential improvements

• Back up the Pi regularly so you don't get in the same situation I did, making recovery harder
• If you want things to be tidier, and you don't mind sacrificing your Pi and also making debugging harder, just run the Pi inside your meter box with Wifi. You will need an electrician to install a power point though. 
• Ensure you don't expose any electronics, in Australia we have big spiders and geckos that love my meter box 
• A dedicated Arduino with RS485 adapter and ESP8266 wifi would be cheaper, entirely sufficient and maybe even more resilient if all you want to do is send data to PVoutput.org or anywhere else 
• Link this setup with emonCMS (openenergymonitor.org) and/or home-automation.io 
• If all your host does is log Solar, it might as well shut down overnight, you could use a shutdown script after dark (don't just power it off!!) and an external timer to turn it off and back on before dawn.