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I've been playing with the ATmega328 and xbee a lot and wanted to take it to the next step and make it fully mobile. So i have decided to use 2xAA batteries along with a 5V step up to get a stable 5V output (link) for the ATmega328, and a 3.3V step down to power the xbee.

The 5V step up is a LT1300 and the 3.3V step down is a MCP1700 (). The ATmega328 is using the Arduino bootloader and code.

My problem is that the ATmega328 is not responding when using the LT1300 even though the output is a nice and clean 5V. It is working thought if I replace the LT1300 schematic with a regular 5V DC power source.

Any ideas as to why this might be happening?

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matejj
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  • Ok i have found the solution... a simple 1uF decoupler on pin 7 & 20 fixed the problem. I didn't think this would be necessary as the step up already has decoupling. – matejj Mar 05 '12 at 05:58
  • Doesn't the xBee module work at 3V? In that case you could directly use the battery voltage... – clabacchio Mar 05 '12 at 09:02
  • @clabacchio I don't think using the battery voltage directly is a good thing – abdullah kahraman Mar 05 '12 at 09:16
  • @matejj could you post an oscilloscope screenshot of the 5V rail without the decoupling capacitor? I am really curious how the signal looks! – abdullah kahraman Mar 05 '12 at 09:18
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    @abdullahkahraman I don't mean using it to power the ATmega, just the xBee module: it seems a waste to use a step-up and then a step-down... – clabacchio Mar 05 '12 at 09:28
  • You got to step-up both. 2xAA are 3V and it's not going to stay constant, right? – abdullah kahraman Mar 05 '12 at 13:50
  • Sorry I don't have a scope... i'm using a multimeter. @clabacchio the battery voltage is not constant and drops rapidly. Using this particular step-up allows for stable voltage even with only 1.8V output from the batteries. – matejj Mar 05 '12 at 21:38
  • But for instance I'm using a wireless module that works with any voltage from 2V to 3.6 without problem...that's why I was asking – clabacchio Mar 05 '12 at 21:44
  • @clabacchio what module are you using? is it an xbee? – matejj Mar 08 '12 at 03:49
  • @matejj no 802.15.4 – clabacchio Mar 08 '12 at 05:26

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Ok i have found the solution... a simple 1uF decoupler on pin 7 & 20 fixed the problem. I didn't think this would be necessary as the step up already has decoupling.

matejj
  • 31
  • 4