Board occasionally resetting when dropped or knocked

Question

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.

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? — The Photon, Apr 27 '13 at 00:18
Some microcontrollers have a way to distinguish from among several possible reasons for a reset, which can be interrogated upon the next startup. — Kaz, Apr 27 '13 at 02:29
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. — geometrikal, Apr 27 '13 at 03:07

XMPPwocky · Answer 1 · 2013-04-27T00:17:12.143

3

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.

edited Apr 27 '13 at 00:17

answered Apr 27 '13 at 00:00

XMPPwocky

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There are the typical SMD bypass caps. X5R I think. Would they suffer from microphonics? – geometrikal Apr 27 '13 at 03:14
Yes, they certainly could. Do you have a scope? – XMPPwocky Apr 27 '13 at 04:31
Got a scope, will see if some knocks affect the voltage – geometrikal Apr 27 '13 at 05:06

score 0 · Answer 2 · answered Apr 27 '13 at 06:44

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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.

answered Apr 27 '13 at 06:44

jippie

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Ah, but the problem appears on multiple boards. – XMPPwocky Apr 29 '13 at 00:12

Board occasionally resetting when dropped or knocked

2 Answers2