Everything depends on the project status volume. For 100pcs an LDO of 1euro is damn expensive. At volume LDO (at 100pcs) must be in 0.15-0.2euro/pcs If wrong choosed, 3.3V and 5V are an issue, you can see this after the first 100 programming times... when need to switch jumpers. No probnlem with one hobby board. Thermal dissipation on 3.3V could be also a problem. Imagine a communication bus at 120mA (maybe you don't need it, like RS485) and a common unstabilised power supply of 9V input (need 4V dropout on common/inexpensive 5V LDO). The 3V3 stab will dissipate 9V-3.3V =5.7V*0.12A = 0.7W Size can be another problem if 10% of your board is occupied with a TO220 which is loaded with 1W. For hobby it's good, but those hobby projects will be someday production projects... I see this based on your complicated code.
best wishes, Vasile On 9/1/09, AlbertF <[email protected]> wrote: > > > Hi Richard, > Maybe use a LD1117, not too expensive 0.5..1 Euro, not too hard to > find (local electronics shop) and available in TO220 housing (homebrew > friendly_) > > http://nl.farnell.com/stmicroelectronics/ld1117v33/v-reg-ldo-3-3v-1117-to-220-3/dp/9755837 > Albert > > > > > > On 1 sep, 11:04, Richard <[email protected]> wrote: > > Hoi Seb and Albert, > > > > In our situation I would like to use a LDO because the dropout voltage > > of the LM317 can exceed the 1.7V (I >= 500mA Tamb < 25degree). > > > > What about the LM2937ET-3.3? or the LF33CV (seewww.rs-components.com > > artnr: 355-4128) > > > > -Greetz > > > > Richard > > > > On 31 aug, 23:30, "a.faber" <[email protected]> wrote: > > > > > > > > > If the 3.3 volt regulator is hard to find, why not design it with the > good > > > old LM317 and two resistors? > > > Albert > > > > > ----- Original Message ----- > > > From: "funlw65" <[email protected]> > > > To: "jallib" <[email protected]> > > > Sent: Monday, August 31, 2009 11:13 PM > > > Subject: [jallib] Re: Jaluino next version: what could be > added/improved > > > > > Hi Sebastien, > > > > > I looked again on Arduino site at their hardware specifications > > > starting from Nano, Diecimila to Duemilanove and Mega. All boards are > > > using the 5V source for powering the microcontroller and the board. If > > > an external source is lower than 7V can cause board instability. > > > The 3.3V power is provided by FTDI and can draw a maximum of 50mA. Is > > > provided for shield and is fragile in my opinion. > > > Jaluino can have a more powerful regulator. Having a 3.3V source > > > available for shield is a good option (very handy). > > > > > But, if others can't easily find a 3.3V voltage regulator, the board > > > still can be built and used because 3.3V is only for shield use (if > > > required - it can be soldered later). Anybody can find a 7805 5V > > > regulator. > > > > > My opinion... > > > > > Regards, > > > Vasi > > > > > On Aug 31, 10:13pm, Sebastien Lelong <[email protected]> > > > wrote: > > > > Hi Richard, > > > > > > I can't guess which is the most used, which make more sens: > > > > > > 1. 3.3V/5V selection for board and shield, or > > > > 2. 5V on board and 3.3V shield with voltage adjustments... > > > > > > If we follow Arduino design, I think (but I'm not sure it is the same > on > > > > all > > > > *duino flavors) it corresponds to just 3.3V on spare pin, that is > option > > > > 2. > > > > > > > > OK, I'll try to find one of these. > > > > > > I've ordered more copper clad boards & more stuff on eBay, I hope > to > > > > receive > > > > > > them this week so I can build this upcoming board next WE. > > > > > > > Lets hope the next one will be the final one for Jaluino Medium > > > > > homebrew > > > > > > Don't worry for me about building many boards, I expected this, and > this > > > > is > > > > a mandatory and very important step. (and I need to see it for real > to > > > > figure out what should be modified, etc...) > > > > > > Cheers, > > > > Seb > > > > -- > > > > Sbastien Lelonghttp://www.sirloon.nethttp://sirbot.org > > > > > > 2009/8/31 Richard <[email protected]> > > > > > > > Hello Seb, > > > > > > > > > Ok, I will only add 3.3V to spare pin of the power connector, > but am > > > > > > > afraid i will at least need to add 1 via and maybe more :-(. > > > > > > > > Do you mean it would be simpler if you put 3.3V selection and all > the > > > > > > whistles about 3.3V ?... :) > > > > > > > Well, it is quit simple to make +5V selectable between 3.3V and 5V > > > > > because the traces dont need to be changed so except for serial > > > > > connector (this better stay on 5V) all +5V when selected on 3.3V > will > > > > > become 3.3V so on power connector that +5V will also become 3.3V > > > > > (spare stays unconnected). > > > > > > > above is easier but if you want the main board on 5V and need only > > > > > 3.3V for the shield (and off course dealing with the voltage level > > > > > adjustments on the shield) this would be impossible. > > > > > > > But every time when you need 3.3V on a shield you also want to > power > > > > > your main board with 3.3V so that you dont have to deal with > voltage > > > > > level adjustments, well than it is the easiest way. > > > > > > > In my opinion is 3.3V on the spare pin of the power connector AND > 5V > > > > > selectable between 3.3V and 5V the most flexible option (but off > > > > > course also the most impact on the pcb) > > > > > > > > OK, I'll try to find one of these. > > > > > > I've ordered more copper clad boards & more stuff on eBay, I hope > to > > > > > receive > > > > > > them this week so I can build this upcoming board next WE. > > > > > > > Lets hope the next one will be the final one for Jaluino Medium > > > > > homebrew > > > > > > > > Cheers, > > > > > > Seb > > > > > > > Greetz > > > > > > > Richard- Tekst uit oorspronkelijk bericht niet weergeven - > > > > > - Tekst uit oorspronkelijk bericht weergeven - > > > --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
