I have a board that consists of

  • Arduino pro mini (ATMega328P, ceramic resonator, tactile reset button)
  • SD card
  • I2C sensors
  • LTC3525 boost converter (IC, inductor, caps)

Very occasionally, if the board is accidentally dropped or knocked it will reset. Unfortunately I cannot seem to reproduce the problem, but it has happened on multiple boards.

Any ideas what the problem could be? My guess is the force of the drop actuates the reset button, or perhaps stops the resonator for a split second.

Edit: The board also has 2 x AA battery holders.

  • 1
    \$\begingroup\$ How are you proving power to the board? If you're using batteries, could they be losing contact with the circuit when it gets dropped? \$\endgroup\$
    – The Photon
    Apr 27 '13 at 0:18
  • 2
    \$\begingroup\$ Some microcontrollers have a way to distinguish from among several possible reasons for a reset, which can be interrogated upon the next startup. \$\endgroup\$
    – Kaz
    Apr 27 '13 at 2:29
  • \$\begingroup\$ @ThePhoton ahhh yes, there some AA battery holders. Thanks. \$\endgroup\$ Apr 27 '13 at 3:02
  • 1
    \$\begingroup\$ Thanks @Kaz I didn't even think of that. I can check the MCUSR register to see if it was a watchdog, brownout, power on, or external reset. \$\endgroup\$ Apr 27 '13 at 3:07

The resonator might be affected, but stopping the clock usually shouldn't cause a reset.

Are there any ceramic capacitors on the board? They can sometimes have sudden temporary changes in capacitance in response to shock/vibrations- this causes voltage spikes, which can easily cause a reset.

I'd watch the reset pin on a scope or logic analyzer and see if you actually see it trigger. If you do, it's likely the switch. If you don't, check the caps; if they're fine, I have no idea.

  • \$\begingroup\$ There are the typical SMD bypass caps. X5R I think. Would they suffer from microphonics? \$\endgroup\$ Apr 27 '13 at 3:14
  • \$\begingroup\$ Yes, they certainly could. Do you have a scope? \$\endgroup\$
    – XMPPwocky
    Apr 27 '13 at 4:31
  • \$\begingroup\$ Got a scope, will see if some knocks affect the voltage \$\endgroup\$ Apr 27 '13 at 5:06

Carefully tap the board with the back of a small screwdriver and see if you can find a pot on the board where it is sensitive to tapping. It sounds like you have a bad soldering or a bad contact in the various connectors you have.

  • \$\begingroup\$ Ah, but the problem appears on multiple boards. \$\endgroup\$
    – XMPPwocky
    Apr 29 '13 at 0:12

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