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Topic: Questions on making a minimal/custom Arduino circuit @ 3.3v/8Mhz? (Read 3 times) previous topic - next topic

xl97

hey gang.. title says it all.. :)

I have never created/designed a Arduino circuit/board that runs on 3.3v @ 8Mhz before..

I currently have a fun project/challenge that calls for one.. but I want to make sure I understand everything I have read over the months on this subject.. to ensure I havent skipped anything.. or have any unexpected surprises...etc

FACTS:
This custom design/pcb will have uSD socket on it..
Board needs to have minimal design components (space is a HUGE obstacle here), but till somewhat stable
Board will run @ 3.3v
Board will run @ 8Mhz internal clock
Battery solution I 'believe' is a very small coin cell (exact choice hasnt been finalized yet)



QUESTIONS:

1.) If the board is running @ 3.3v/8Mhz (like a pro mini or something).. do I need 'any' sort of level/logic converting for the uSD card then?  (whether it be an IC or a simple resistor voltage divider..etc)?? 

2.) Since the battery used will be more or less a 3.3v (under 5.v for sure, since the only space is really a coin cell type of solution... grrrr)...  can I get away with NOT using any sort of voltage regulator?.. and having a few polarized caps along the input/power traces?

3.) being a MINIMAL design is a focal point.. what IS the minimal (but still somewhat stable/safe) components needed?
     a.) 10k resistor for reset pin
     b.) cap for DTR breakout

*since running @ 3.3v/8Mhz.. I wont need a 16Mhz xstal, no 2 x 22pF caps, no vReg??
Im at a loss?  any suggestions to help me plan correctly here?


4.) programming a 'blank' Atmel328 (TQFP) chip to run @ 8Mhz internal clock?
I have programmed blank chips before (both dip and smd) using my Arduino 2009 board, with Arduino as ISP..
I have since moved on to using the Optiloader sketch written my Arduino 2009 board.. and flashed the Opiloader bootloader to my custom/assembled boards..etc..
Everything I have done uses 16Mhz external  crystal/caps..

but reading, it seems you need to have the crystal/caps installed/set-up (connected to chip) in order to even WRITE a new 3.3v/8Mhz bootloader?  (fuses are set at factory to use external 16Mhz clock?).....

So I could also use some clarification on the easiest way to just flash a bootloader (not even sure which one? pro-mini? lilypad?) that runs @ 3.3v and internal 8Mhz clock..

I have no 'AVR' type programmers, just an Arduino and the IDE..etc..

knowing this.. any suggestions in general? (outside of the specific questions I asked)

Thanks!

oric_dan

If you want to see a minimalist Arduino ckt, running at 3.3V, check out the schematics
for the JeeNode. You can replace the RF module with your SD card.

http://jeelabs.com/products/jeenode

You can flash bootloaders using the ICSP header, or SCK,MISO,MOSI pins, of any Arduino
board connected to your protoboard, although both boards should probably be running
at 3.3V. Check the main Arduino website.

xl97

hmm.. I have read (several times I thought) about problem with buring bootloader for 3.3v @ 8Mhz on factory/blank chips?  as they are set to run at 16Mhz external clock?  so you need to have caps/crystal connected "FIRST"..  then burn the 3.3v/8Mhz bootloader of choice?


is this NOT the case your saying?


(I have flashed all my chips/boards using the ISP headers and Arduino IDE..like I mentioned... but never done anything with 3.3v boards or running anything @ 8Mhz... so I wanted some clear advice..)

To clarify.. your saying that my Arduino 2009 board than I use to flash bootloaders to OTHER blank chips, needs to somehow run @ 3.3v now? in order to burn the target (3.3v/8Mhz) bootloader of choice to the blank chip?


thanks for link to jeenode.. (looking at it now)

Riva

Quote
hmm.. I have read (several times I thought) about problem with buring bootloader for 3.3v @ 8Mhz on factory/blank chips?  as they are set to run at 16Mhz external clock?  so you need to have caps/crystal connected "FIRST"..  then burn the 3.3v/8Mhz bootloader of choice?

The default factory fuse settings are to use internal oscillator.

CrossRoads

Select a 3.3V/8MHZ board type that is comparable to your hardware setup.
Ex:
You have 8 MHz crystal: select 3.3V/8MHz Promini.
You have no crystal, but want 8 MHZ - select Lilypad 00 or Lilypad 01 if the options exist:

LilyPad Arduino 00

The initial design of the Arduino LilyPad had a 10-pin ICSP header and used the internal clock on the ATmega168 rather than an external oscillator.
The bootloader on the initial design is the traditional NG bootloader.

LilyPad Arduino 01

In the first revision of the LilyPad Arduino the 10-pin ICSP header was changed to a 6-pin ICSP header and a four pin header w/ RX, TX, +5V, and GND was added.



Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

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