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[on:]

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.

[Reply #1 on:]

Here are some pictures

[Reply #2 on:]

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.

[Reply #3 on:]

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.

[Reply #4 on:]

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

[Reply #5 on:]

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".

[Reply #6 on:]

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..

[Reply #7 on:]

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 .

[Reply #8 on:]

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

[Reply #9 on:]

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

[Reply #10 on:]

@ 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).