Logic Level Converter -> XBee 3.3v / AtMega328p 5v

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1

I have read a lot about this subject to safely interface my xbee to an atmega328p running on 5v. I have a logic level converter from sparkfun which its schema is available on http://www.sparkfun.com/datasheets/BreakoutBoards/Level-Converter-v10.pdf. It works perfectly of course.

But, I don't want to use one of this on my final circuit so I made a circuit and I changed the BSS138 with a 2N2222 because I don't want to do SMD soldering. So, my question is: is it safe?

My actual schema is attached.

Thanks,

Wagner Sartori Junior

logic_level_converter.png
logic_level_converter.png864×540 4.71 KB

2

Well, a MOSFET is not exactly interchangeable with a BJT, but you've got the right idea. I would move the 10k resistor to be in series with the transistor base, and then connected to +3.3V.

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3

Like this?

logic_level_converter_v2.png
logic_level_converter_v2.png864×540 4.11 KB

4

Yes.

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5

Ok, I'll make the circuit and test it before I plug my XBEE ;).

Thank you very much for your help.

6

TX part(transistor) is working fine.

The RX part(voltage divider) is not OK and I don't know why. I tried using 2 x 10k, 10k+22k and 2.2k+3.3k resistors. None of them make it work.

Using sparkfun's logic level converter, works perfectly. My circuit is exactly as showed onmy last schema uploaded to this thread.

7

Can you measure RX3V with a DMM? Is it about 2.5V when there is no serial activity?

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8

It's measuring 3.3v not 2.5(2 x 10k is half right?).

RX from atmega328p is measuring 4.62v.
RX to xbee is measuring 3.3v.

Also I measured both resistors(they are 5%) and are OK.

9

It sounds like you have connected to an output on the XBee instead of an input.

Try disconnecting RX3V from the circuit then you should measure ~2.5V at the center of the two resistors. Then, check your wiring and see what's going on with that RX3V pin and why it's an output instead of an input.

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10

you're righ. all my circuit are inverted(RX/TX) on both sides.

newbie error, sorry :wink:

thank you it's working fine now.