I would like to make the board as universal as possible to fit any projects I may attempt so I plan on passing through as many digital and PWM lines with low pass filters as possible. I would also like to include a voltage regulator and possibly an FTDI interface if its easy enough to do. I have created a rough schematic in eagle but being a noob I didn't want to push forward into board design without someone more skilled checking it over for obvious mistakes.
components so far include
-atmega 328
-db25 connector (male or female)
-6 4.7K resistors
-6 2.2uf capacitors
-voltage regulator (7805 most likely)
-10k resistor for reset pin
-16mhz ceramic resonator
I can't find an "attatch" button so I will simply upload it to megaupload.
couple more questions...Do I need to put grounded caps around the voltage regulator's in and out pins? Does this filter out noise? Do I need to connect the AVCC pin to 5V with a low pass filter if I plan on using the ADC? Are the resistors and caps I chose correct? I have tried to compile this from multiple tutorials but the library still confuses me :-?
What do you mean by buffering? Why is the 12V signal inverted? I have what I assume to be the same setup soldered on a generic radioshack pcb board without the caps and it runs alright, but i think I'll splurge for the filtering.
I think Osgeld is assuming you will be programming directly from the computer's serial port. If that is the case you need something like a MAX232 to change the RS232 voltage levels.
If you are programming it with one of the many FT232 based boards, you are ok.
EDIT:
I just noticed you mentioned the FTDI chip in your post, so if you are already using something like that, then you don't have to worry about RS323. I don't see why you couldn't fit a USB chip on there. I have a Atmega1280 + FT2332 in less than 3sq inches.
if you want usb, but check digikey, I think they have a less featured larger package chip, some of the lower pin count SOT styles are not much harder than what your used to ...
and in your schematic I assume that large d-sub connector is a 232 port, they by nature are
-12 = logic 1
+12 = logic 0
inverted, and out of range, if you hook that up to a logic chip without buffering it to your working voltage it will kill it
this goes back to the days of teletype where long distances and grumpy mike age technology needed a stout signal to overcome shortcomings (its also why you can send 232 or its cousins down pretty darn long lengths of unshielded untwisted wire), the inversion is another byproduct of the old tech vs cost (and is actually still quite common today)
course you can handle that with a couple transistors if speed is not a factor (I dunno 9600 to 14400 bps or so, maybe more), or a handful of different ways
if your not using it for serial communications I would at least use the wrong connector (pc serial ports are male at the computer) so someone doesnt go plugging it in to a RS232 port , which would be the first thing I think of seeing a subD hood with a female jack on its end
The DB25 port is strictly there to fulfill the design of the enclosure as a custom connector and I have no intention of ever plugging it into a serial port. I will gladly make it a male to avoid any possible accidental confusion.
I looked on digikey but couldn't find an interface with less than 28 pins and those seemed to be the same size or model than the ft232rl I found on sparkfun.
The FT232RL in that package isn't too hard to solder. But if you are etching your own board, you may have issues etching that small depending on the technique you use.
An easier way to do it would be to search ebay for "SSOP28" You'll see plenty of boards that will adapt that size package into a manageable size that will allow for breadboarding.
I would worry more about the actual USB connector.
I was planning on getting the board professionally done online somewhere so that shouldn't be an issue. I'll just have to buy the proper tools to solder the surface mount FT232RL. The USB port also shouldn't be an issue as I plan on having the usb pin lines come out through the DB25 connector and then attach to a male usb type a cable. My main goal of this PCB is to have everything fit inside this enclosure and all lines come in/out via the DB25 connector. I'll add the caps on the vreg, a low pass on the AVCC as well as the FT232RL.
I'll just have to buy the proper tools to solder the surface mount FT232RL.
You can do this with a regular solder iron. As long as there is a solder mask on the board and you have some extra flux it won't be a problem. Once you do it you will see how easy it is. It's not necessary to have to solder each pin individually. Just run the solder iron across them all. Worst case you'll get a solder bridge that some solder wick can pick up.
On the datasheet (page 24) it shows 2 0.1uf caps as well as a 4.7uf cap grounding VCC, any reason to add a 4.7uf cap or is it not relevant in this case?
Thanks for all your help guys! It would have taken me ages to figure this stuff out on my own.
Thanks in advance!
