XBEE voltage drop

Other Hardware General Electronics
1

Hi there, i'm posting here because i'm running out of ideas and i'm stuck:
I've been programming a little robot in order to use some programs I wrote, based on two xbee communicating and controlling things.

Now i wanted to turn it into the real world and embbed everything on the robot:

I've got a 9Volt battery powering an arduino MINI on +9V
my embedded xbee transceiver is powered by the same battery, on which i plug a little adjustable voltage divider.

I configure the divider to provide +3V because xbees need 2,8 - 3,3 .
when i plug the xbee in, it is not detected. The arduino still works fine.
I measure a drop of voltage between Vcc and GND of the XBEE ( he now has 1,8v and any of my potentiometer do not allow me to get higher )

have you ever heard of anything like that? What advice could you give me.

NB: my xbees work fine, i still can program them, when i use two breakout boards, the two xbees still communicates, so i'm sure it has NOT burned.

2

  1. yeah, you can't power an XBee using a voltage divider, you need to use a real 3.3V
    voltage regulator.

  2. then, you will also need to use 5V-to-3.3V level-shifters on the TX signal from the
    Arduino.

  3. also, you cannot connect both USB port and XBee to the Arduino R,Tx pins at the
    same time, so you need some sort of switch.

  4. a little 9V battery will not power either robot or Arduino or XBee for very long. You
    should use something better, like AA or AAA cell packs.

3

1st of all, thanks for your time

oric_dan:

  1. yeah, you can't power an XBee using a voltage divider, you need to use a real 3.3V
    voltage regulator.

what would you call a "real" 3.3 regulator? would you have a specific component

i'm not using the xbee when i'm uploading some code, i always reconnect everything ( always the same code running for ever in fact )

so you think my 9v battery does not provide enough current and i should move to lipo or things like that?

4

The best choice of v.reg depends upon the module being used. The basic XBee draws
low currents, so any TO-92 100mA v.reg will do. The XBee Pros draw in the range of
250 mA, so you need a much larger current capacity v.reg. I've used both TO-220
LM1117-3.3 and DPAK NCP1117-3.3 devices.

And don't forget the level-shifters.

I use NiMH AA-cells in all my robots, and don't much mess with Lipo myself. The little
9V cells will power an Arduino board, but not for very long, and they'll go flat a lot faster
if also powering Xbees. The NiMH AA-cells have 2000-2500 mAh, but 9V batteries only
600 mAh or so.

5

OK i'll try this out tomorow,
thanks a lot for your help, it's good to have ppl here with experience.
i may post here again if anything seems wrong.