I've just had my delivery of a 3.3v Arduino Pro Mini as I'm transferring my project from 5v to 3.3v. I have the official Arduino FTDI serial adapter and wanted to know if 1) Its safe to use it, 2) if so will the voltage regulator send the 5v supply from the computer to the raw pin?
The reason why is because most of my sensors are 3-5v except one which explicitly needs 5v to run. When powering it externally I will be using a 9v battery which will be regulated to 5v then sent to the raw pin, so my date and time module that needs the 5v will simply share "raw" rail on the breadboard while everything else will use the 3.3v power rails. If I can get 5v to the raw pin when using the FDTI I can debug, etc. when re-writing the sketch. If not its going to be difficult.
The circuit shown in that diagram looks OK. The Pro's regulator will drop the voltage to 3.3V.
When you connect the FTDI's data lines to the pro (CLK, MISO, MOSI) you might be sending 5V signals to a 3.3V chip. I'd put in some resistors to limit the current. 5K sounds about right to me.
You can get FTDI adapters with jumpers to select 5V/3.3V. It might be worth investing on one...
Come to think of it, a 9V battery to power a 5V project does not sound sensible. If you must, I would think a high performance switchmode regulator (module) would be the go. But then, there are obviously a lot of other pieces to this puzzle ...
I do normally put a few 0.1uf capacitors on my ins and outs, just didn't bother illustrating them in my diagram.
Hmm, completely confused now :~ Its so annoying when different components need different voltages and references for the analog ins!! And expensive...
Come to think of it, a 9V battery to power a 5V project does not sound sensible
Its a 3.3v project. I have powered 5v projects with PP3's and I've not had any problems. Also a switch mode regulator sounds to over complicated as its only a tiny data logging box.
fungus:
When you connect the FTDI's data lines to the pro (CLK, MISO, MOSI) you might be sending 5V signals to a 3.3V chip. I'd put in some resistors to limit the current. 5K sounds about right to me.
unless im missing something here that ftdi is serial (rx/tx) not isp and not capable of 5v output, only 3.3v.
i dont see any need for a regulator since the promini has one. and 4 aa cells would probably last 5-10 times longer than a 9v and cost a lot less. specially rechargeable.
I'm not to sure why SPI was mentioned earlier either :~
i dont see any need for a regulator since the promini has one. and 4 aa cells would probably last 5-10 times longer than a 9v and cost a lot less. specially rechargeable.
The regulator is there so I can send 5v to just one sensor, namely a DS1307 real time clock, otherwise like you say I wouldn't bother with one and use 4 aa cells as that would be 6v and more ampage compared to a pp3.
I've ordered a 3.3v Sparkfun FTDI adapter as my Arduino FTDI is 5v
i think youll find all ftdi (pl2303) put out 3.3v or less regardless of supply voltage so that shouldnt be an issue. and has 3.3v internal regulator so, like with promini, is available there too. also note that using ldo type regulator would allow 5v from 4 cells. good luck and let us know how it works out.
