Telemtry issue


i noticed that my ESC's regulator outputs 5.5 ish volts, and i thought it is ok, but it seams that my xbees, (2.4gh xbee pro series 2) doesn't like it so much, it just won't connect, so i have a 5v regulator (L7805) i connected it, and everything works like a charm now, so i guess i'll try to use the onboard regulator to power my xbees, doesn't it output 5v to the telemport?

i guess i'll know soon enough !!

i read somewhere around here that someone had a similar problem, i hope this might be of help to him/her, i mean that the xbees are serious about the little over voltage.

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  • Sounds like you've solved the issue, supply the system with only 5 volts,  or supply the APM with a little higher voltage and use the regulator on the APM to give the APM 5 volts.


    Here's why the input voltage may matter.

    The main 1280 or 2560 atmel controller on the APM is running at the input voltage to the board  (your 5 volts or 5.5 volts).   or if use a battery or offboard regulator with maybe 7? volt minimum, and select the 5v regulator on the APM board,  then it will be getting 5 volts.        I think this matters because all the digital input lines on the atmel detect a 'high' signal if the input voltage is .6 x the Vcc voltage      

    see page 367 of the datasheet:  


    .6 * 5 = 3.0 volts,     .6 * 5.5 = 3.3 volts         Why would that matter?   The communication between the atmel and various other items (the gps, the xbee, the magnetometer) are all some sort of serial communication.  input lines to the microcontroller that get switch high, lo, high, lo.     If the high signal that is coming back in is 5v high, and 0v low,  should be definitely no problem.    but.....   if the other device runs at a lower voltage, like 3.3,  and there isn't something special done, then the 3.3 volts that it sends out as 'high', may not be enough to register as 'high' in the APM. 


    The something special would be a level shifter, to translate the 3.3v signal up to 5v, so it's clearly high.   

    There is an 'I2C translator' on the oilpan, I assume that does levelshifting for the magnetometer and baro pressure sensor and anything else on the I2C bus.   So I bet no issues with those.

    The mediatek gps adapter supplies 3.3v locally to power the gps, but I don't think there's any level shifter on the lines back to the 2560 serial port.  I get a possibly similar problem with my gps,, if i use a 5.5v BEC to power everything.

    I have these ladyada xbee adapter boards  and they have a level shifter, and my xbee seems to work fine even with using a 5.5v BEC to run it all.

    Does your xbee adapter board have a level shifter on it?  There are a few different adapter boards with various features (or not..)  Probably the adapter board does have a 3.3v voltage regulator on it, but maybe not a level shifter to bring the 3.3v output from the xbee up to 5v for the 2560.


    For the 5v regulator on the APM, what is the minimum supply voltage for it, is it a low dropout regulator?  Would it work to give 5.5v to the batt input of APM and solder the jumper?

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