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Messages - brett

Project development, ideas, and suggestions / Re: Which comes first?
sorry for resurrecting the thread (I was searching out the latest on BLiVIT and came across this post).

LiFePO4 is certainly not the same chemistry as Li-Ion or LiPo.  The giveaway is the cell voltage, nominally 3v2 not 3v7.  The charge and discharge thresholds are very different as @blarson notes.  But then again, most 18650 cells you buy are Li-Ion not LiFePO4, so unless you have a certain supplier I'd go back to checking what your actual chemistry is. ... -cell.html  is an example cell that is LiFePO4.

As for current limiting and isolation, I would think that current limiting is still relevant, you want to protect against a device that has failed. And I think the isolation should be to isolate the battery from the load, and not the boosted, regulated output.
Project development, ideas, and suggestions / Re: Power charger and supply regulator
I guess if they're "open" projects then you don't really lose anything by publishing, since that would be a goal anyway? But yeah I'd probably say it's worth checking out what ramifications (the bad stuff, for you) there are associated with publishing something in a well-respected location, in fact I'd be surprised if they didn't have a guidance pack for contributors.
Project development, ideas, and suggestions / Re: Power charger and supply regulator
Great idea, I too think there's a lack of solutions that manage charge AND supply at the same time. It's great to see someone thinking about this - I haven't the expertise to do so, so I like that you're articulating decisions too, can help me think about my scenario.  I also want to use a solar panel (which I have been looking at LT3652 power tracking / charge chip for).
Project logs / Re: Brett's Solar Inverter custom PCB
Thanks Ahri, yes if I intended to do more, I probably would - I can see the value in it after this last try !  :)

All things considered I should have also given it more time, I only allowed 4 mins like the printed instructions that came with the board said, even though on my first board I left it for closer to 10 (like it says on the web)
Project logs / Re: Brett's Solar Inverter custom PCB
Toner tip: it takes time to heat the copper board to melt the toner, and to have it transfer from Press-n-peel paper to the board.  It takes a fair amount of even pressure too. Trying to shortcut by ironing two small boards together doesn't save time nor make for good results.  Do them separately and you'll save yourself time in the long run. Ask me how I know :(
Project logs / Re: Brett's Solar Inverter custom PCB
no etching yet. Etchant I have needs to be made up to 70*c.  It also says that it takes 5-10 minutes to etch the board, and that you have to keep the solution at ~70*C. Anyone with tips on that?  Think the best I can plan on is using a couple of small containers, one as a water bath, and to continue to replace the water bath water regularly with freshly boiled.
Project logs / Re: Brett's Solar Inverter custom PCB
well a heavy week saw this kicked off the schedule. Last night I fired up the iron (SWMBO's blessing and all), and ironed the toner onto the copper board.  Pic to come. Etchant will get fired up today once I have home duties sorted.  Luckily for the PCB it's raining so I've got no hope of being asked to mow the lawn :)
Project logs / Re: Brett's Solar Inverter custom PCB
never say never - twice.

Found I had some 75mm wide stock single sided PCB so instead of buying a new larger board and cutting to 80mm, you guessed it, revised the board and shrunk 5mm off the narrow side. 

Now I'm calling DONE for good. :)
Project logs / Re: Brett's Solar Inverter custom PCB
Fundamentally, I didn't get a lot of control over things you mention.  “In an ideal world”…. :)  Absolutely I can see the reason you approach things that way, I would too – although I have that little constraint of Eagle board limit of 100x80 to contend with so laying out can be somewhat constrained even in that scenario :)

Just to document the thought pattern a little more, here's a marked up version of the last image, red numbered boxes around the major component locations:

1 is the DS18B20 one-wire device plus a 2.54mm pin headers for extension off the board if needed.  Data pin can go to pretty much any IO pin location.

2 is the 24LC256 I2C eeprom.  The I2C pins must go to the identified pins.

3 is the WIZ812 module (40 IO pins in 2x10 x2 configuration). Only a small number of the pins are used in the SPI configuration I'm using.  Some of the pins need to go to the SPI specific pins, then there are a number that go to the GPIOs.  (Just above it is the 4pin header that will go to the RS232 daughterboard.)

4 is the Fez Panda IO header locations. These come directly from GHI's design files, are not separate-able at all, can only be moved as a block.  One of the first things I did was take GHI's component-level design and strip out all the irrelevant components just leaving the headers so that I had precise header location rather than measuring them.  The headers remain as individual items in the Eagle file - I couldn’t really figure how to take a schematic plus board layout and make that a “component” so I just left it as-is and was careful not to move it.

5 is the SD card holder I talked about earlier and created a footprint for.  Pin selection is fixed for the majority of the pins, except the outermost two lines on each side (the signal lines for the detection of card inserted and write-protect).  As you can see the connections there were quite challenging. Because I’m making a single-sided board the routing was much a harder than it would have been had I been able to mount the card holder on the other surface (most lines unravel themselves).  Oh well :)

I fail the ERC since there are unconnected GND and VCC nets (they’re connected by the Panda that I will plug into this board).  I fail DRC (based on what I think I should use for home-built PCBs) on numerous things, the simplest is that I have a couple of manual wires that I have planned to cross, some of the harder ones are the clearance of header pads from the GHI files.  I couldn’t figure out how to deal with the crossed-wires without resorting to a new layer, but because I know what they are and that they’re irrelevant, I am fine leaving things “dangling”.

Anyway, so besides all the issues I know about, the board really isn’t something I can be bothered optimising beyond this – I am sure there’s a lot of things I could do but again as a one off there’s no return on it, I am just moving on!

Thanks Ian for the 2nd visit :)
Project logs / Re: Brett's Solar Inverter custom PCB
Eagle finding #1. 

When I was deciding on the routing for ethernet and SD card detection pins (ie any that didn't have pre-defined destinations on the board), the best thing I found was figuring out the directions traces would run and deliberately chosing pins that gave the longest parallel runs. Once I did that, the layout seemed to go together really well. 

To do this I didn't follow what a "traditional" layout process would be. I initially had added all the components in schematic view, and wired up the known / mandatory pin connections (like the SD card pins, plus GND/VCC).  Then I went into PCB view and laid out what I thought would give me room for routing the other data lines.  After that, I had a rest for a couple of weeks away from Eagle (this step is highly recommended but totally optional).  Then I figured out what traces would come from where, and laid them out in my head as parallel runs - then figured out what pins I needed to connect to (and were available) and switched back into schematic view and connected the nets, then back on the PCB I laid out the traces.

(there, +1 for documenting things I learnt)
Project logs / Re: Brett's Solar Inverter custom PCB
Hi Mick, and thanks for taking a look and the time to comment.

you're right, it is a little hard to make true detailed suggestions without schematics etc.  But given the very specific nature of this project, plus the very limited "design" pieces (I basically am throwing down known devices and connecting them), I suspect there's not really much value to be had for either you or I in getting the files to look at them.

The main reasons I started the project log were:
* show off my first Eagle efforts (and how ham-fisted they were), and document some of my learnings along the way (although I didn't detail some of that shame on me)
* discuss home-etched PCBs incl what I thought would be the hardest part, drilling thru-holes - maybe get some tips from others who do prototype PCBs at home on limited equipment.

It wasn't really to get routing assistance, or electronics guidance, but to make some mistakes and learn from them.

I'd be interested to hear what your thought was about getting the files, what you'd look at and comment on etc, while I figure out a place to put them.  In the meantime the next best thing I can do is a screenshot of Eagle in board view.