LM317 need Vin=Vout+3V to work properly. http://www.national.com/ds/LM/LM117.pdf page5
Your schematic is redundant, why do you need two LM317 since only one VDD level is used (+3V3 OR +5V)? use the jumper on the R8, without jumper you'll have +5V, with jumper make R8 parallel with R8a so the equivalent resistor will be 390 and you'll have 3V3 at the output. In that way you cut down three silly jumpers: SJ6, SJ7 and SJ8 and replace those with one. Vasile On Sat, Jan 22, 2011 at 6:33 AM, Sebastien Lelong < [email protected]> wrote: > Hi guys, > > As I mentioned some times ago, I'm trying to design a new Jaluino board, > named Jaluino Bee because it needs a name. This idea is to provide a very > small board, very cheap, thus using SMD components. It would include a Xbee > socket, as a standard way to plug many different communication modules (real > Xbee/ZigBee, RF, USB, ...). I'm trying to make it as modular as possible. > Depending on usage, user would solder require components or not. For > instance: > > - use USB or not > - crystal or internal clock > - use 5V, 3V3, both or no voltage regulator (none could be used to > directly power the board using batteries for instance). Based on adjustable > vreg LM317. > - or power the board through a serial module or USB > - use I²C or not > - Reset via RTS option > - CTS/RTS option > - connectors for pin header: plug on a breadboard (male) *or* used to > plug potential shields (female) > - ICSP connector > - serial connector > > > Attached is a first schematic draft. No PCB design yet, I don't know if all > of this will fit within 5x5cm or smaller. But I guess so. > > Schematic is for PIC18F27J53, SOIC package, but I identified at least 2 > other interesting chips: > > - PIC18F2550: quite common, USB inside > - PIC18F25K22: for high speed application (up to 64MHz), lots of mem, no > USB > > More may also fit. > > As for SMD design, I followed advices and used 1206 resistors and > capacitors, as they are easier to solder. I also wanted to use SOIC package > for MCU, easier to solder than SSOP for instance. There are a lot of > jumpers, due to modularity. I'm hesitating: either using PTH jumpers, or > solder jumpers. First are interesting when tinkering with the board, they > can be always changed. But they are very tall. Solder jumpers cannot be > easliy changed. I then figured out it may be possible to solder 0805 0ohm > resistor over PTH jumper traces (0805 is 0.08" long, PTH space between pins > is 0.1"). This way user can choose between a flexible, ready-to-tinker > modules (PTH) and something more definitive (using 0 ohm resistors). What do > you think ? > > Every component I'm using here seem to be easily available. But because > it's kind of painful to source components, I may provide most of them > (except MCU) if it appeared to be manufactured. > > Any advices, thoughts, feedback appreciated. > > Cheers > Seb > -- > Sébastien Lelong > http://www.sirloon.net > http://sirbot.org > > -- > You received this message because you are subscribed to the Google Groups > "jallib" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]<jallib%[email protected]> > . > For more options, visit this group at > http://groups.google.com/group/jallib?hl=en. > -- You received this message because you are subscribed to the Google Groups "jallib" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/jallib?hl=en.
