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[on:]

I use the arduino to monitor the tempreture of a vehicle engine.  It ran for a few weeks but then one day the battery ran flat (very old battery), I replaced it but my arduino stopped working.  I tried reset but it still wouldn't start.  I  reloaded the hex and it started working again.  I recharged the old battery and connected it to the arduino again.  A few days later the battery was flat again and the exact same thing happened to the arduino.  

Is there anyway that low voltage could cause the hex to be wiped?  I have tried different boards and chips but can't find a clear pattern.

[Reply #1 on:]

First what do you mean by wiped HEX? Does that mean you are losing the sketch code but the bootloader code still allows you to reload the sketch from the Arduino IDE?

The AVR chip does have voltage brown-out detection ablility (holds processor in reset if voltage goes below a certain threshold) but I don't know if and how or if the Arduino sets it up or even uses it. Perhaps someone else knows.

Lefty

[Reply #2 on:]

Is there anyway that low voltage could cause the hex to be wiped?

It could be that as the battery went flat there was a voltage that caused a reset, then noise on the input pins caused the boot loader to think a new program was being downloaded and it erased the flash in preparation for this, which never came.

Just a guess but it is feasible.

[Reply #3 on:]

Indeed also.........as the voltage dropped and hovered around the point the Arduino boots this caused multiple and continious shutdown/resets and could have crashed the cpu mem.

Ian.

[Reply #4 on:]

recharged the old battery and connected it to the arduino again.  A few days later the battery was flat again and the exact same thing happened to the arduino.  

It could be that as the battery went flat there was a voltage that caused a reset, then noise on the input pins caused the boot loader to think a new program was being downloaded and it erased the flash in preparation for this, which never came.

Just a guess but it is feasible.

Ok, I would go with this story for once in my lifetime, but two times?

Maybe if the board is glued to a microwave oven or WiFi router..

Eberhard

[Reply #5 on:]

For what it's worth...  I have a radio (a Yaseu VX-1R) that has similar symptoms.  When the battery gets very weak the radio loses all of it's setup information.  After the battery is replaced I have to go through an extensive manual reprogramming procedure to get it working again.  (I stick to Kenwoods or Icoms now.)

Don

[Reply #6 on:]

For what it's worth...  I have a radio (a Yaseu VX-1R) that has similar symptoms.  When the battery gets very weak the radio loses all of it's setup information.  After the battery is replaced I have to go through an extensive manual reprogramming procedure to get it working again.  (I stick to Kenwoods or Icoms now.)

The symptoms reported by the OP sound more like  
the device forgot it was a Radio in the first place   ;D

But seriously:
Is anything connected to the pins 0 and 1?
If not you could permanently pull them high with a 10K resistor.
Eberhard

[Reply #7 on:]

I've had the same thing happen to me, but with a simple blinky light skech and a 9v battery.
Program seems to be wiped, uploading it again solves it.

Nothing was connected except a couple leds (and a small piezo I think).

[Reply #8 on:]

I have to ask: Why aren't you running the Arduino off the vehicle's battery instead?