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Topic: Allduino (bluetooth, lipo battery+charger, ATMEGA328P, FTDI) Eagle Design (Read 3353 times) previous topic - next topic

zeroplus

Hi all,

I have this rather ambitious first project in the works (ambitions for a person of my more modest skill level at least).  I was hoping to get some opinions on my design in Eagle.  I might find this to be a huge mistake in the future but I tried to do the whole thing in one go instead of coming here and asking for each and every part of it first.  Instead I have what I hope is a final product and this is what it is:


  • 3.3V regulated by ultra-low dropout LDO

  • ATMEGA328P at 8MHz

  • LiPo powered

  • Battery charging IC from USB (MAX1811)

  • Micro-USB

  • FTDI USB->UART

  • HC-05 bluetooth Serial Port Profile module (from ebay)

  • Really small PCB size (~50mm x ~20mm)

  • Low profile ~7mm? (eyeballing it; height of microusb + height of ftdi + PCB thickness)



I attached the Eagle files and the Gerbers in the zip file (in case someone who wants to look at it doesn't use Eagle).  In addition, I have already had it fabbed by SeeedStudio's Fusion PCB service (which is awesomely cheap I must say; for someone just starting out it's nice to not burn a hole in my pocket only to find out later that this kinda thing isn't for me).  I have every part I need except the 10uF caps right now and have populated everything I could.  So far the power rail seems to be working well but without the caps I dare not go any further for now.

What I'm looking for are any mistakes I may have made, improvements I can make (on my Eagle design, software suggestions, bluetooth device ideas, etc).  I have extra boards in case someone decides they want one.  They come with 2 panelized on a 50x50mm board one with ground planes and the other without.  The BOM is not particularly cheap but since this is for a University project I managed to get the majority of important components on sample orders.

Lastly, this is one of my few experiences on a forum and my first on this one in particular so feel free to take a shot at me if this post is in the wrong place.

PS. I am open to making this a commercial thing if ever it comes to that.

Lemme know how I did with this first project of it's kind for me.

Edit: I should also note that this is a 3.3V LDO version.  I am in the process of replacing the (rather large) LDO for a switching power supply to bring it to a 5V rail.

zeroplus

Here are some pictures

Fat D

Cool thing, but forcibly tying the BT module to a software serial means it cannot be moved to the hardware serial for cool stuff like wireless programming and such.

zeroplus

Yea I remembering pondering that for a ver long time. I opted to go for a tethered solution first and I could later tie those two together. I just lose the use of two pins is all.  My project requires two uarts and I did not want to bump it to a mega IC..

Other than that, i bet I could use this as  a peripheral prototyping board for android or windows 8 or something.

I have like 8 spare boards with two boards per board lol. Need some use cases.

Edit: moment of clarity! I remember worrying about the FTDI and the bluetooth in conjunction with another load sinking too much current on the pin and becoming indeterminate.  Perhaps Im paranoid.

pito

..btw - are you using 2.5mm pitch? That is not 0.1" however..

zeroplus

I'm not sure if I understand. Is which part 2.5mm. And 2.54 mm if im not being stupid is indeed 0.1".

pito

Your grid in allduino.brd is set to 0.25mm, so the Q is whether the span between the both pinheaders is metric or inch..

zeroplus

Oh. That header footprint is from sparkfun's library i think. Itll be the standard 0.1". But even if someone says its 2.54 mm i wudnt be surprised if saying 2.5mm is same. Thats a really insignificant rounding for only 15 pins.  Bottom line is that headers fit fine on my part :).

Graynomad

Quote
The BOM is not particularly cheap

What is the cost in 1 and 100 off? I'm curious because I've also just done a board so I'd like to see how expensive mine is :)

You have two caps on DTR.

Why two crystals?

The schematic doesn't have chip types so no (convenient) way to verify them.

Looks very good, especially for a first-timer.

______
Rob
Rob Gray aka the GRAYnomad www.robgray.com

pito

ok :)
BTW you can do wireless programming - see the other topic on it. Just connect 100nF capacitor from pin 32 of the BT to the reset. Mind the close/open the BT connectivity resets arduino then (when capacitor is connected).
http://arduino.cc/forum/index.php/topic,132006.0.html

zeroplus

@ Graynomad

Lol do u mean the cost of pcb fab? Mine was dirt cheap. 6mil everything (vias, traces etc).  10 boards is  13.50 including shipping so like 70 cents a board. I didnt actually calculate the BOM.  What are u trying to 'verify'.

Edit: the ftdi, hc-05, max1811 and the vreg (analogue devices adp24 something i think) arent the cheapest. For instance. The max1811 could instead be a max1511 but i wanted to be able to source more current. Also the switching power supply ic i have in mind would be around 5$ for the 5v version. Also, the battery connector is NOT the standard jst 2 pin. Its a molex panelmate low profile connector. If im not mistaken, the eagle schematic shud have all that in the part info.

Anywho, there was a question as to which crystals would be available so originally i had two footprints since i had space. Granted the trace capacitance might affect the clock but thats a gamble. If anything ill just scratch that trace to cut the extra off.

In the end, if u look at the footprint on the same side as the micro, i made the side traces larger to accomodate anyway. So really i dont need that second one.

And yes, i kno i can program wirelessly but ive never really been too interested in doing so (and also where the hell am i gonna fit the extra traces/vias without too much work, i have upwards of like 40 vias already lol).  Its easy enough for someone to enable that by doing some external wiring.

Edit: when I say crystal, i really mean ceramic oscillator cause that's what it is.  Not nearly as accurate as a crystal but it'll do (and it's tiny).  The PCB fab I used was http://www.seeedstudio.com/depot/fusion-pcb-service-p-835.html (dirt cheap).

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