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).

Nov 192017
 

So, this weekend I did plan to run from solar full time to see how it’d go.

Mother nature did not co-operate.  I think there was about 2 hours of sunlight!  This is what the 24 hour rain map looks like from the local weather radar (image credit: Bureau of Meteorology):

In the end, I opted to crimp SB50 connectors onto the old Redarc BCDC1225 and hook it up between the battery harness and the 40A power supply. It’s happily keeping the batteries sitting at about 13.2V, which is fine. The cluster ran for months off this very same power supply without issue: it’s when I introduced the solar panels that the problems started. With a separate controller doing the solar that has over-discharge protection to boot, we should be fine.

I also have mostly built-up some monitoring boards based on the TI INA219Bs hooked up to NXP LPC810s. I have not powered these up yet, plan is to try them out with a 1ohm resistor as the stand-in for the shunt and a 3V rail… develop the firmware for reporting voltage/current… then try 9V and check nothing smokes.

If all is well, then I’ll package them up and move them to the cluster. Not sure of protocols just yet. Modbus/RTU is tempting and is a protocol I’m familiar with at work and would work well for this application, given I just need to represent voltage and current… both of which can be scaled to fit 16-bit registers easy (voltage in mV, current in mA would be fine).

I just need some connectors to interface the boards to the outside world and testing will begin. I’ve ordered these and they’ll probably turn up some time this week.

Aug 132016
 

Sometimes I wonder.  Take this evening for example.

I recently purchased some microcontrollers to evaluate for a project, some Atmel ATTiny85s, because they have a rather nice PLL function which means they can do VHF-speed PWM, and some NXP LPC810s, because they happen to be the only DIP-package ARM chip on the market I know of.

The project I’m looking at is a re-work of my bicycle horn… the ATMega32U4 works well, but the LeoStick boards are expensive compared to a bare DIP MCU, and the wiring inside the original prototype is a mess.  I also never got USB working on them, so there’s no point in a USB-capable MCU.

I initially got ATMega1284s owing to the flash storage, but these being 40-pin DIPs, they’re bigger than anticipated, and the fact they’ve got dual USARTs, lots of GPIOs and plenty of storage space, I figured I’d put them aside for another project.

What to use?  Well I have some AT89C2051s from way back (but no programmer for them), some ATTiny24As which I bought for my solar cluster project, an ATMega8L from another project, a LeoStick (Arduino Leonardo clone).  The LeoStick I’m in the process of turning into a debugWire debugger so that I can figure out what the ADCs are doing in my cluster’s power controller (ATTiny24A).

I started building a programmer for the ‘2051s using my ATMega8L last weekend.  The MAX232 IC I grabbed for serial I/O was giving me jibberish, and today I confirmed it was misbehaving.  The board in general is misbehaving in that after flashing the MCU, it seems to stay in reset, so I’ve got more work to do.  If I got that going, I was thinking I could have PCM recordings in an I²C EEPROM and use port 1 on the ‘2051 with an R2R ladder DAC to play sound.  (These chips do not feature PWM.)

Thinking this morning, I thought the LPC810 might be worth a shot.  It only has 4kB of flash, half that of the ATTiny85, and doesn’t have as impressive PWM capabilities, but is good enough.  I really need about 16kB to store the waveforms in flash.  I do have some I²C EEPROMs, mostly <2kB ones that are sourced off old motherboards, but also a handful of 32kB ones that I had just bought especially for this… but then left behind on my desk at work.

I considered audio compression, and experimenting with ADPCM-style techniques, came to the conclusion that I didn’t like the reduced audio quality.  It really sounded harsh.  (Okay, I realise 4-bits per sample is never going to win over the audiophiles!)

Maybe instead of PCM, I could do a crude polyphonic synthesizer?  My horn effect is in fact synthesized using a Python script: the same can be done in C, and the chip probably has the CPU grunt to do it.  It’d save the flash space as I’d be basically doing “poor man’s MIDI” on the thing.  Similar has been done before on lesser hardware.

I did some rough design of data structures.  I figured out a data structure that would allow me to store the state of a “voice” in 8 bytes, and could describe note and timing events in 8-byte blocks.  So in a 2kB EEPROM, I’d store 256 notes, and could easily accommodate 8 or 16 voices in RAM, provided the CPU could keep up at 30MHz.

So, I pull a chip out, slap it in my breadboard, and start hooking it up to power, and to my shiny new USB-TTL serial cable.  Fire up lpc21isp and, nothing, no response from the chip.  Huh?  Check wiring, probe around, still nothing.  Tried different baud rates, etc.  No dice.

This stubborn chip was not going to talk to lpc21isp.  Okay, let’s see if it’ll do SWD.  I dig out my STLink/V2 and hook that up.

OpenOCD reports no response from the device.

Great, maybe a dud chip.  After a good hour or so of fruitless poking and prodding, I pull it out of the breadboard and go to get another from the tube it came from when I notice “Atmel” written on the tube.

I look closer at the chip: it was an ATTiny85!  Different pin-out, different ISP procedure, and even if the .hex file had uploaded, it almost certainly would not have executed.

Swap the chip for an actual LPC810, and OpenOCD reports:

Open On-Chip Debugger 0.10.0-dev-00120-g7a8915f (2015-11-25-18:49)
Licensed under GNU GPL v2
For bug reports, read
http://openocd.org/doc/doxygen/bugs.html
Info : auto-selecting first available session transport "hla_swd". To override use 'transport select '.
Info : The selected transport took over low-level target control. The results might differ compared to plain JTAG/SWD
adapter speed: 10 kHz
adapter_nsrst_delay: 200
Info : Unable to match requested speed 10 kHz, using 5 kHz
Info : Unable to match requested speed 10 kHz, using 5 kHz
Info : clock speed 5 kHz
Info : STLINK v2 JTAG v23 API v2 SWIM v4 VID 0x0483 PID 0x3748
Info : using stlink api v2
Info : Target voltage: 2.979527
Warn : UNEXPECTED idcode: 0x0bc11477
Error: expected 1 of 1: 0x0bb11477
in procedure 'init'
in procedure 'ocd_bouncer'

I haven’t figured out the cause of this yet, whether the ST programmer doesn’t like talking to a competitor’s part. It’d be nice to get SWD going since single-stepping code and peering into memory really spoils a developer like myself. I try lpc21isp again.

Success!  I see a LED blinking, consistent with the demo .hex file I loaded.  Of course now the next step is to try building my own, but at least I can load code onto the device now.