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Topic: mixing 3.3V and 5V in a very tiny space (Read 1 time) previous topic - next topic

davidb

Hi all,
Thank you all so much for the replies! What it's highlighted is a deficiency in my electronics knowledge, however (and I must say I've had quite a whirlwind education over the past couple months!)! If I understand correctly now, simply having a 3.3V power source for the xbee and a 5V supply for the others will not do...I must also convert the serial (TTL) messages between the two!

The adafruit version seems ideal, but it's a bit too large some of my applications. Sparkfun also has one:
http://www.sparkfun.com/commerce/product_info.php?products_id=9132
however there seems to be quite a few answered questions wrt level shifting (whether it does it) and 150mA vs 250mA current threshold. Actually the other sparkfun BOB mentioned above seems lovely, if only it didn't need both power sources (the size is certainly right). @EmilyJane: slick is ideal! But the concern is also what the max the xbee can receive as logic 1 without creating smoke, which is what I am trying to figure out now.  Actually does anybody know what the minimum voltage the pro mini can accept as logic 1 input (r the max the xbee series 1 can handle)?

Anyway, thank you all for the advice. So much more to learn! And here I thought 12 years of college was enough :)

Cheers,
David

EmilyJane

#6
Jun 29, 2009, 08:49 am Last Edit: Jun 29, 2009, 09:02 am by EmilyJane Reason: 1
It looks like both protect the XBee from being over-driven from 5V logic. Depending on what is on the 5V side, it looks like neither meet minimum drive levels. The minimum guaranteed logic 1 output from the XBee is 0.82*Vcc or 2.7V.

The minimum logic 1 input for the Atmega168/328 is 0.6*Vcc.

If you operate the Arduino at 4.3 V, it will run at 16 MHz and the XBee will meet its Vih specs. :)

davidb

Hi all,
To sort of conclude the conversation here, I received a handful of the sparkfun devices:
http://www.sparkfun.com/commerce/product_info.php?products_id=9132

...and am a very happy camper. Now everything can exist in 5V land...and there was much rejoicing.

Best,
David

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