Looking for feedback on brewing shield with touchscreen

Social Project Share
41

@AndyW, I was thinking something along these lines:

http://webench.ti.com/webench5/power/webench5.cgi?VinMin=11.00&VinMax=13.00&O1V=5&O1I=0.8&base_pn=LM2675&AppType=None&op_TA=30&lang_chosen=en_US&optfactor=3

LM2675MX-5.0, with low ESR 47u or 68u output capacitor and 47uH or 68uH coil.
This chip gives a much higher efficiency than the LM2595 (90% vs 82%).

WeBench gives an 8mV output ripple at 260kHz.

Total BOM count is 7, so it is still pretty small. Only 4 more than the LDO.

42

Looks good.

Pay attention to the layout with the lm2675.

43

@AndyW
I designed the new version, with the switching power supply. I hope you can look at it and critique my layout.

Other changes:

  • Pull down resistors on ACT1-ACT3
  • Pull up resistor on BUZZ (to 5V, pin is not 5V tolerant, but with 10k resistor).
  • Input cap on ADC changed to 10n
  • 10n input cap on touch screen interrupt pin (this is the trace closest to the coil)
  • 6p terminal block instead of 3x2p, cheaper

And of course I had to move everything to make room.

New schematic:

PCB:

http://gerblook.org/pcb/MXHrnx8ztU74CmPrLH6JgP#front

1 Like
44

Hi Elco,

Just a couple comments:

  • C4ā€™s return is quite longā€¦ see if you can get that ground connected more directly to the Coreā€™s GND.
  • As a general practice, the planes under L1 should be split in the middle with a gap, vs. shifted to one side like you have it. Or better yet, remove the ground plane under the inductor completely. Unless the inductor is a shielded type, then it doesnā€™t matter much, but Iā€™d still gap it center it just because I might not be able to buy a shielded type of inductor down the road. The ground plane on the bottom under the inductor is not serving a purpose for heat or much for current either, so you could clear it away there as well. Do some research on this as well, this is kind of stuff I do because Iā€™ve run into issues in the past during EMI testing and SMPS tuning. YMMV :slight_smile:
45

Thanks for the feedback @BDub.

  • C4 return path is GND pin on header --> bottom plane --> GND pin on spark. Itā€™s not that long? I can place it under the spark core though and it will be shorter.
  • The plane under the inductor is 5V, not GND. The datasheet had the plane split like this in their reference layout. The inductor is a shielded one: http://katalog.we-online.com/pbs/datasheet/7447714680.pdf
  • The plane on the bottom is all GND
46

Ahh, okā€¦ didnā€™t see that GND pin on the 3 pin connector. Thatā€™s not so bad, but ideally you want both legs of the cap to be between the the input connections and connections to the spark core.

If you have a reference design, definitely go for that first. Itā€™s shielded anyway, so no worriesā€¦ just a more expensive part. Reference designs are a good place to start, but also be cautious as they are not always going to give you what you need.

Donā€™t be afraid to stitch your GND planes from top to bottom a bit moreā€¦ itā€™s basically free.

47

love this idea.
i have a lot of touchscreens and spark cores lying around. would love to help where i can.

48

Hi Korneel,

Are you Dutch by any chance? Your name sounds Dutchā€¦

If you want to help write the code for this board, I can send you a prototype.

Elco

49

Hi Elco;

yes i am dutch :smile:
would love to help you, i am great in copy pasting code and troubleshooting stuff, not so much in writing blank code.
still happy to help.

50

I soldered the new prototype and the things I have tested so far seem to work :smile:

Switching power supply tested at 89% efficiency at 400mA (12V to 5V).

3 Likes
51

Nicely done!

52

Not only does it look greatā€¦I think you have done an awesome job in the short time that you have been working on this projectā€¦Just simply very well doneā€¦Wish I have the electronic and programming skills to help push it down the road to completion just a bit faster as Iā€™m very eager to try it outā€¦

1 Like
53

Glad I didnā€™t place my order for the BrewPi shield tonight before looking at this thread.
Is it too late to start looking at using the Photon instead of the Core?

PS. Can I preorder the BrewPi Spark Shield?

Thank you

54

It is too early to use the Photon instead of the core :smile:
I plan to have these in stock in 3 weeks. When the Photon is ready, it will replace the core.

Pre-orders will be possible after the official announcement.

55

this is awesome! very excited to pre-order

1 Like
56

excuseme but ther is the modbus library in the library list? i donā€™t found it.

57

Sorry for the lack of updates guys. I have a big one here: http://www.brewpi.com/introducing-brewpi-spark/

Because it comes with enclosure and all, I decided to call it the BrewPi Spark, instead of BrewPi Spark Shield.
I hope thatā€™s okay, because every unit will have a spark core inside I thought it was appropriate.