I'm just beginning to learn Eagle in anticipation of getting a few small custom boards made and I'm wondering what crystal Felix used that is so tiny. I'm just using the default Eagle and SparkFun libraries but it seems like all the crystals they contain are gargantuan compared to the roughly 2x1mm crystal on our Moteinos. Can someone point me in the right direction for which crystal does the job in so compact a package please?
It's actually a ceramic resonator: http://www.digikey.com/product-detail/en/CSTCE16M0V53-R0/490-1198-1-ND/584635
Thanks Felix! That probably should have occurred to me when scrutinizing your .brd file since I did notice 3 pads under the part. I still have much to learn when it comes to PCB layout...
Additionally, as a new Eagle user, you MUST learn about ulps, especially exp-lbr.ulp.
Tom
Thanks Tom. I was unaware of that concept other than I've been using statistics but I'll look into those. Attached is my latest attempt to lay out a TH node using a 328p. This is single-sided to keep things more clear and I've tried to make it as small as possible. I've read a bunch of PCB design tips/guidelines and watched a few hours of stuff on YouTube but I'm sure I've still made some faux pas if not mistakes. Is there a place online where folks can get feedback from experts on PCB layout? I don't know that this forum is the right place for that even if someone felt charitable.
Thanks,
ChemE
Quote from: ChemE on December 23, 2016, 08:02:27 PM
Is there a place online where folks can get feedback from experts on PCB layout? I don't know that this forum is the right place for that even if someone felt charitable.
Thanks,
ChemE
There are no shortage of 'experts' on this forum! ;)
Looking at your design I have a couple of observations, but overall, its a good job for a newbie!
1. You should connect AVCC and AGND pins, even if you are not using an analog input.
2. Filter caps on VIN are recommended. 0.1uF is generally accepted practice. I put one cap on each of the four sides of the processor (to catch VCC and AVCC) and AREF. Since you're not using analog input you can skip the cap on AREF.
3. The VIAs are precariously close to SMT pads. Solder may disappear into the via, leaving the pad 'dry'. You have two choices: Move the vias further away from the pads or remove the 'stop' layer from the vias so that the via pad doesn't flow solder.
4. Are you going to use a stencil and solder paste? If so, I would recommend removing the 'cream' layer from the RFM69 pads and not reflow solder the RFM69 (solder this by hand).
EDIT: 5. Learn to use the 'Smash' control so that you can maneuver the silk screened text to clear space.
That's all I see with a quick glance.
Let us know how it comes out!
Tom
Quote from: TomWS on December 24, 2016, 09:22:49 AM
3. The VIAs are precariously close to SMT pads. Solder may disappear into the via, leaving the pad 'dry'. You have two choices: Move the vias further away from the pads or remove the 'stop' layer from the vias so that the via pad doesn't flow solder.
4. Are you going to use a stencil and solder paste? If so, I would recommend removing the 'cream' layer from the RFM69 pads and not reflow solder the RFM69 (solder this by hand).
EDIT: 5. Learn to use the 'Smash' control so that you can maneuver the silk screened text to clear space.
That's all I see with a quick glance.
Let us know how it comes out!
Tom
Thanks for your feedback Tom it is much appreciated. I'm not too familiar with what the tStop layer does but I think it maps out where the solder resist should be omitted. I didn't realize early on that I was creating untented vias. I have since learned to tent my vias and lay in copper pours to be used as ground planes. I had not contemplated my solder running off nearby pads and taking up residence in an untented via but that sounds like hard won experience that I'm quite happy to avoid. I was planning to use a stencil and solder paste on the top of the board and reflow in a toaster but you are right, I was planning to mount the radio underneath by hand since it is so large. Another new discovery for me; the cream layer. I'll post a revision or two for further feedback if you don't mind. I also went ahead and pulled the trigger on a monster $3.05 order from OSH Park yesterday on a teeny little board that adapts the RFM69CW to pins 15-22 of a 328p-DIP28 (skipping pin 20 -AVCC obviously). I'm on the 27th panel and pretty excited to be making the leap away from breadboard and perma-proto boards!
Quote from: TomWS on December 24, 2016, 09:22:49 AM
2. Filter caps on VIN are recommended. 0.1uF is generally accepted practice. I put one cap on each of the four sides of the processor (to catch VCC and AVCC) and AREF. Since you're not using analog input you can skip the cap on AREF.
In trying to look into this design practice, I'm confused by what the filter caps do for pins 9-16 and 25-32. Also, in looking at the board file for the Mote r4 it looks like Felix runs a ground to directly under the center of the 328p and doesn't connect it to anything. Is that for thermal reasons to conduct heat away from the chip?
EDIT: Ah, I see that the 28 pin MLF package does have a ground in its center.
Quote from: ChemE on December 25, 2016, 12:30:12 PM
In trying to look into this design practice, I'm confused by what the filter caps do for pins 9-16 and 25-32. Also, in looking at the board file for the Mote r4 it looks like Felix runs a ground to directly under the center of the 328p and doesn't connect it to anything. Is that for thermal reasons to conduct heat away from the chip?
EDIT: Ah, I see that the 28 pin MLF package does have a ground in its center.
My bad on this one. Sorry. You're right, it's only two sides for the ATmega328P (pins 4,6, 18, & 20, a single cap on each side). I do use one on RFM69 also, but that could be overkill since it has its own caps.
Tom
Quote from: TomWS on December 24, 2016, 09:22:49 AM
There are no shortage of 'experts' on this forum! ;)
...Let us know how it comes out!
I wanted a smaller/simpler test of my nascent PCB design skills, and I bought a bunch of RFM69Ws cheap from Anarduino (best price I've found on these guys), so I whipped up a teeny little board to accomplish a few things.
1) Be small/cheap to have fabbed
2) Work super friendly with a 328p DIP of which I have many
The 328p DIP really does want to get married to an RFM69W if you look at the placement of MOSI/MISO/SCK/NSS. And VCC and GND are virtually next door. Finally, there is a spare pin on that side of the chip which could serve as DIO0 rather than routing the signal around to pin4 (PD2). I haven't done the last yet but I've seen threads where it is done apparently. You actually don't need DIO0 to send packets so a TH node can just skip DIO0. All that for this:
BOB Close-Up(http://i44.photobucket.com/albums/f26/cdl1051/Close_Up_zpswreggzh4.jpg)
BOB Installed in Bare Bones Setup(http://i44.photobucket.com/albums/f26/cdl1051/In_System_zps6azfoslq.jpg)
These cost me $1.02 each from OSH park and the eagle files are attached. This little guy works like a champ with exactly 0 changes to Felix's library. I still need to work out the code needed to let it receive since that does involve setting an interrupt handler on pin 15.