Jan 242018
 

So, I now have my little battery monitoring computer.  Shipping wound up being a little more than I was expecting… about US$80… but never mind.  It’s here, arrived safely:

HTLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLFLC
>> TS-BOOTROM - built Jan 26 2017 12:29:21
>> Copyright (c) 2013, Technologic Systems
LLCLLLLLLLFLCLLJUncompressing Linux... done, booting the kernel.
/ts/fastboot file present.  Booting to initramfs instead
Booted from eMMC in 3.15s
Initramfs Web Interface: http://ts7670-498476.local
Total RAM: 128MB
# exit
INIT: version 2.88 booting
[info] Using makefile-style concurrent boot in runlevel S.
[ ok ] Starting the hotplug events dispatcher: udevd.
[ ok ] Synthesizing the initial hotplug events...done.
[ ok ] Waiting for /dev to be fully populated...done.
[ ok ] Activating swap...done.
[....] Checking root file system...fsck from util-linux 2.20.1
e2fsck 1.42.5 (29-Jul-2012)
/dev/mmcblk2p2: clean, 48540/117600 files, 282972/469760 blocks
done.
[ ok ] Cleaning up temporary files... /tmp /lib/init/rw.
…
ts7670-498476 login: root
Linux ts7670-498476 2.6.35.3-571-gcca29a0+ #1 PREEMPT Mon Nov 27 11:05:10 PST 2017 armv5tejl
TS Root Image 2017-11-27

The programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.

root@ts7670-498476:~# 

The on-board 2GB eMMC has a version of Debian Wheezy on it.  That’ll be going very soon.  For now, all I’ve done is pop the cover, shove a 8GB MicroSD card into one of the on-board slots, wired up a 12V power brick temporarily to the unit, hooked a USB cable into the console port (/dev/ttyAMA0 is wired up to an on-board CP2103 USB-serial chip) and verified that it is alive.

Next step will be to bootstrap Gentoo.  I could use standard ARMv5 stages, or I can build my own, which I might do.  I’ve done this before for mips64el n64 using glibc.  Modern glibc is a goliath on a machine with 128MB RAM though, so I’ll be looking at either µClibc/µClibc-ng or musl… most likely the latter.

That said, 20 years ago, we had the same computing power in a desktop. 🙂

I have a few options for interfacing to the power meters…

  • I²C, SPI, a number of GPIOs and a spare UART on a 2.54mm header inside the case.
  • Another spare UART on the footprint for the GPS module (which my unit does not have)
  • Two RS-232 serial ports with RTS/CTS control lines, exposed via RJ-45 jacks
  • Two CANbus ports on a single RJ-45 jack
  • RS-485 on a port marked “Modbus”

In theory, I could just skip the LPC810s and hook this up directly to the INA219Bs.  I’d have to double check what the TTL voltage is… Freescale love their 1.8V logic… but shifting that up to 3.3V or 5V is not hard.  The run is a little longer than I’m comfortable running I²C though.

The LPC810s don’t feature CANbus, so I think my original plan of doing Modbus is going to be the winner.  I can either do a single-ended UART using a resistor/diode in parallel to link RX and TX to the one UART line, or use RS-485.

I’m leaning towards the latter, if I decide to buy a little mains energy meter to monitor power, I can use the same RS-485 link to poll that.  I have some RS-485 transceivers coming for that.

For now though, I’ll at least get Debian Stretch going… this should not be difficult, as I’ll just use the images I’ve built for work to get things going.  I’m downloading a Jessie image now:

root@ts7670-498476:~# curl https://bne.vrt.com.au/technologicsys/ts7670d-jessie-4.4.1-20160226.dd.xz | xzcat | dd of=/dev/mmcblk0 
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0  113M    0  544k    0     0   114k      0  0:16:48  0:00:04  0:16:44  116k

Once that is done, I can reboot, re-format the eMMC and get debootstrap going.  I might even publish an updated image while I’m at it.

Jan 172018
 

I’ve taken the plunge and gotten a TS-7670 ordered in a DIN-rail mount for monitoring the battery.  Not sure what the shipping will be from Arizona to here, but I somehow doubt I’m up for more than AU$300 for this thing.  The unit itself will cost AU$250.

Some will argue that a Raspberry Pi or BeagleBone would be cheaper, and that would be correct, however by the time you’ve added a DIN-rail mount case, an RS-485 control board and a 12V to 5V step-down power converter, you’d be around that figure anyway.  Plus, the Raspberry Pi doesn’t give you schematics.  The BeagleBone does, but is also a more sophisticated beast.

The plan is I’ll spin a version of Gentoo Linux on it… possibly using the musl C library to keep memory usage down as I’ve gone the base model with 128MB RAM.  I’ll re-spin the kernel and U-Boot patches I have for the latest release.

There will be two functions looked after:

  • Access to the IPMI/L2 management network
  • Polling of the two DC power meters (still to be fully designed) via Modbus

It can report to a VM running on one of the hosts.  I believe collectd has the necessary bits and pieces to do this.  Failing that, I’ve written code before that polls Modbus… I write such code for a day job.

Dec 252017
 

So, I’m home now for the Christmas break… and the fan in my power supply decided it would take a Christmas break itself.

The power supply was purchased brand new in June… it still works as a power supply, but with the fan seized up, it represents an overheating risk.  Unfortunately, the only real options I have are the Xantrex charger, which cooked my last batteries, or a 12V 20A linear PSU I normally use for my radio station.  20A is just a touch light-on, given the DC-DC converter draws 25A.  It’ll be fine to provide a top-up, but I wouldn’t want to use it for charging up flat batteries.

Now, I can replace the faulty fan.  However, that PSU is under warranty still, so I figure, back it goes!

In the meantime, an experiment.  What happens if I just turn the mains off and rely on the batteries?  Well, so far, so good.  Saturday afternoon, the batteries were fully charged, I unplugged the mains supply.  Battery voltage around 13.8V.

Sunday morning, battery was down to 12.1V, with about 1A coming in off the panels around 7AM (so 6A being drained from batteries by the cluster).

By 10AM, the solar panels were in full swing, and a good 15A was being pumped in, with the cluster drawing no more than 8A.  The batteries finished the day around 13.1V.

This morning, batteries were slightly lower at 11.9V.   Just checking now, I’m seeing over 16A flowing in from the panels, and the battery is at 13.2V.

I’m in the process of building some power meters based on NXP LPC810s and TI INA219Bs.  I’m at two minds what to use to poll them, whether I use a Raspberry Pi I have spare and buy a case, PSU and some sort of serial interface for it… or whether I purchase a small industrial PC for the job.

The Technologic Systems TS-7670 is one that I am considering, given they’ll work over a wide range of voltages and temperatures, they have plenty of UARTs including RS-485 and RS-232, and while they ship with an old Linux kernel, yours truly has ported both U-Boot and the mainline Linux kernel.  Yes, it’s ARMv5, but it doesn’t need to be a speed demon to capture lots of data, and they work just fine for Barangaroo where they poll Modbus (via pymodbus) and M-bus (via python-mbus).