Author Topic: AB18x5 Breakout Board  (Read 4563 times)

WhiteHare

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AB18x5 Breakout Board
« on: January 08, 2017, 01:44:09 PM »
On a different thread (https://lowpowerlab.com/forum/low-power-techniques/stuck-in-listen-mode-listen-mode-bug-with-workaround/msg16974/#msg16974) I offered to design a simple breakout board for the AB18x5 RTC, so that anyone who wants to try it out will have a way to do so.  For those who don't already know, that AB18x5 RTC uses very little power, making it a good choice for battery based projects.

Attached is the first pass on the breakout board, which should fit easily into any 2.54mm pitch breadboard.  A few open issues:

1.  I wasn't sure if connecting the oscillator directly to pins 15 and 16 might somehow (?) impair its performance.  Also, it's not really necessary.  So, I left them disconnected, but I added some jumper pads so you can connect them after-the-fact if you want to.

2.  I didn't include a GND copper pour.  Not sure if in this case it would help or cause problems, so I left it out.  However, if someone thinks it should have one, I could add it.

3.  The AB18x5 comes in two different versions: one uses I2C, and the other uses SPI.  Rather than do two different boards (with two different silk screens to label the pins), I just numbered the pins.  That way you can use the same board for either chip.

I'll wait a bit for comments.  Then I'll finalize the design and ship off the files to a fab.  After I receive the board and verify that it works, I'll then post the gerber files.


TomWS

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Re: AB18x5 Breakout Board
« Reply #1 on: January 08, 2017, 05:15:34 PM »
A square pad on pin 9 is a bit confusing, especially on the bottom side where there are no pin labels.

EDIT: Also there is no ground signal to the center pad and, on the AB1815 it is the ONLY ground pin.  Consequently this makes 17 pins on the device and you only have 16 on the fanout.  Also if you look at the datasheet for recommend layout, they suggest four small square solder paste areas on the larger pad (this is to keep your chip from floating away when you reflow).  You don't show the cream layer so can't tell from what you have in the design - the same is true for the LGA pads, the cream layer (and stencil) should be smaller than the pad itself.

Just my $0.02...

Tom
« Last Edit: January 08, 2017, 05:26:16 PM by TomWS »

WhiteHare

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Re: AB18x5 Breakout Board
« Reply #2 on: January 09, 2017, 12:58:21 PM »
Thanks!  That's great feedback.

How about Version 2 below?  I used a via to connect the pad under the AB18x5 to a new copper pour on the bottom, which in turn connects to "Pin 17" (in actuality Pin 15 now) on the header.
« Last Edit: January 09, 2017, 02:36:19 PM by WhiteHare »

WhiteHare

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Re: AB18x5 Breakout Board
« Reply #3 on: January 09, 2017, 01:02:36 PM »
More attachments below, including the gerber files.

As for the cream layer, I think I'll try the painting method that you and Joe have developed instead, since this is quantity 1 production.

ChemE

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Re: AB18x5 Breakout Board
« Reply #4 on: January 09, 2017, 08:45:00 PM »
Might as well label the pins on the bottom of the board too since there is room.

perky

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Re: AB18x5 Breakout Board
« Reply #5 on: January 09, 2017, 09:42:10 PM »
I think the AF pin might require a 47pF cap to Vss if you want this to be a purely digital breakout board.
Mark.

WhiteHare

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Re: AB18x5 Breakout Board
« Reply #6 on: January 10, 2017, 11:38:43 AM »
Thanks, guys!  Here's version #3:


WhiteHare

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Re: AB18x5 Breakout Board
« Reply #7 on: January 10, 2017, 11:41:46 AM »
Attached are the version 3 gerber files.

Anyone have any more comments/suggestions?

WhiteHare

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Re: AB18x5 Breakout Board
« Reply #8 on: January 11, 2017, 10:44:43 AM »
As there have been no further comments, I've sent the files to the fab.

As for the components BOM, the oscillator is this one:  https://www.digikey.com/product-detail/en/abracon-llc/ABS07-120-32.768KHZ-T/535-11937-1-ND/3724046

and the capacitor is an 0603 size.  In general, I default to X7R for all capacitors, unless there's good reason not to.

WhiteHare

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Re: AB18x5 Breakout Board
« Reply #9 on: January 22, 2017, 05:53:38 PM »
According to package tracking, I should be receiving my AB1815 breakout boards tomorrow.

@ChemE: Have you found a worthwhile library for the AB1815, or were you planning to build your own from scratch?

At the very least I'd prefer to start with some simple known good sketches so as to test that the hardware is working.

ChemE

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Re: AB18x5 Breakout Board
« Reply #10 on: January 22, 2017, 09:40:19 PM »
I've been playing with my RFM69CW code but I'll have a look tomorrow to see what I can find.  I was absolutely planning on writing my own 'cause that's just the way I roll, but I do like to start from something functional.  Glad to hear they are en route, enjoy your jellybeans!  Lemme know how much you need for one (one is slated to come to me right?).

EDIT: Possible starting points linked below.  Some are vastly more complete than others.
https://github.com/Snowda/AB1805 - minimal but easily taken in
https://github.com/dantudose/AB1805 - in between to minimal
https://github.com/nigelb/Arduino-AB1815 - seems quite complete

I don't see in any of these anything allowing for us to store data in RAM or use the chip as a WDT.  These all just seem to focus on using it as a RTC.
« Last Edit: January 22, 2017, 10:03:09 PM by ChemE »

WhiteHare

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Re: AB18x5 Breakout Board
« Reply #11 on: January 23, 2017, 03:24:34 AM »
LOL.  Well, they cost so little that I don't mind mailing you one for free.  In fact, I thought you had already ordered yours.  But before this gets out of hand, were you planning to solder on the parts yourself, or were you hoping I'd do that too?  I wouldn't want you to miss out on the fun part.   ;)

ChemE

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Re: AB18x5 Breakout Board
« Reply #12 on: January 23, 2017, 08:00:36 AM »
LOL, I thought part of what I was paying for was your advanced soldering expertise.  I don't plan to learn how to hand-solder 0.5mm pitch stuff.  I'm going to let a souped up toaster oven handle that for me so I can concentrate on code.

WhiteHare

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Re: AB18x5 Breakout Board
« Reply #13 on: January 23, 2017, 08:48:32 AM »
In that case, I'll simply wish you good luck.  The files are already posted if you ever want to order one for your toaster oven.

WhiteHare

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Re: AB18x5 Breakout Board
« Reply #14 on: January 23, 2017, 10:18:35 PM »
Attached photo shows how it turned out.  Some of the soldered connections look a bit iffy, but it's really hard to tell for sure just by looking at it.  If it doesn't respond as expected, then I'll attempt some in situ remediation.