Moving on from prototyping

I've been having a fair degree of success with prototyping circuits around an Arduino, to the point where I'd like to build a number of circuits around an AVR core, without the cost and space requirements of a full Arduino in each.

Are there any pointers to how to make this transition? Basically I want to design a PCB with an Atmega processor and other required components on it, and have it behave like the prototype I've built on breadboards.

I would need these devices to remain USB-programmable in the same way as the Arduino, but without a USB connector on board. I don't mind using a breakout board to program them.

Any pointers gratefully received.

You can pretty quickly put together a design for this, and there are a number available (look at, say, the schematics for the really-bare-bones series).

Basics: Read this

If you use a pre-bootloaded ATmega328P (you can install the bootloader with a hardware programmer from the original Arduino board), you only need to include a six-pin header that follows the FTDI pinout for programming. Remember to swap the Rx and Tx pins! (Tx goes to Rx, and Rx to Tx).

Use a ceramic resonator instead of a crystal - you won't have to worry about capacitor selection, which can be somewhat confusing (judging by forum posts).

You have to remember the arduino is almost like any evaluation board.......once you build a circut....you just move the micro to your finished project with just a few support componets....nobody would use a eval board in a finished project...like the other post said, just burn a bootloader into your chip and go.....for USB interface just use a FTDI chip and your set to go.

Thanks for the replies, folks. On the subject of programming the bootloader, the assumption seems to be that the Atmega will be a DIL chip in a socket that can be programmed elsewhere and transferred into the finished project, but I'd rather use one of the surface-mount packages for space savings. How does that work?

You'll need to include a six-pin ISP socket for programming it in-circuit:

Just match the pin labels: SCK, MISO, and MOSI can be found in the datasheet diagrams of the TQFP parts and such.

You can then use the Arduino as an ISP for the permanent board, or buy a hardware programmer separately. In this case, you're probably better off NOT including the FTDI chip, since you can program directly from the ISP and won't really need it (plus it saves space)

Here are my tips, pointers, and lessons learned from doing the following board. This is a picture of an older revision. The newer revision looks much much better. Plus this picture had the solder paste applied by hand and looks horrible.

Background:
This is a special purpose board intended to fit on another board. The other board is a radio control module, but that isn’t important. This board has an ATMega32u4 and a microSD socket.

Regardless if you go SMT or not the first part is the same:
Pick out your chip
Layout your schematic with all the required parts. Draw it out how you have your breadboard.
Layout your board.

If you are in the U.S.A. then I would recommend going through http://dorkbotpdx.org/wiki/pcb_order. It is a group order, they send out a new batch every monday. I get my boards back within two weeks of the monday they go out. I have used Seeedstudio’s fusion service, but I have too many bad boards with broken traces or pads that lifted with the slightest amount of heat. Personally batchpcb was too expensive for me.

If you do go the SMT route, I recommend you get a solder paste stencil. It makes applying the solder paste easier and cleaner (on the board). http://ohararp.com/Stencils.html will make stencils for $25.

No matter what, you will need/want an ISP programmer. I highly recommend getting one. I have this one http://www.adafruit.com/products/46 and have not had any problems with it. I also have http://www.sparkfun.com/products/9825, but it does not work with my laptop. It does work with my desktop, but the adafruit one works on every computer I’ve tried.

You will want the ISP programmer to program your bootloader, set your fuses, and possibly program you chip.

Hope that helps,
J.C. Woltz

Thanks for all the help. I've taken the schematics of Marc Alexander's EtherTen as a starting point, removed all the bits I don't need, replaced some of the components with parts I can more easily source, and redesigned the board layout from scratch. I've ordered PCBs from Beta Layout's PCB-Pool service, and I've been practicing my SMT soldering techniques.

I'll report back when I have the first prototype built.

oscarBravo: Thanks for all the help. I've taken the schematics of Marc Alexander's EtherTen as a starting point, removed all the bits I don't need, replaced some of the components with parts I can more easily source, and redesigned the board layout from scratch. I've ordered PCBs from Beta Layout's PCB-Pool service, and I've been practicing my SMT soldering techniques.

I'll report back when I have the first prototype built.

Depending on how new you are to SMT, stay away from 0603 resistors, caps, etc. Especially if hand soldering. Even with a solder paste stencil, 0805 caps and resistors are so much nicer to work with. If fact, using an SMT stencil will save you time and make the finished board look much much nice. The picture I linked above did not use a stencil. You can tell by the uneven solder paste application.

I've designed for a minimum size of 0805. I've managed to assemble a board with some 0603 components, but it was fiddly.

PCB-Pool are including a free stencil with each board design, which is nice - but is solder paste really useful if I'll be hand-soldering?

@oscarbravo: check this out:
http://www.ladyada.net/make/boarduino/

oscarBravo:
I’ve designed for a minimum size of 0805. I’ve managed to assemble a board with some 0603 components, but it was fiddly.

PCB-Pool are including a free stencil with each board design, which is nice - but is solder paste really useful if I’ll be hand-soldering?

If you will use SMT, then yes you will want solder paste. For through hole parts you don’t need or want to use solder paste. When I first started with SMT I got some solder paste from digikey for less than $20.
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=SMD291SNL-ND
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=SMD291SNL10-ND

I’ve never used this, but spark fun has some for $10: