Vibration Problem

Dustin C

Hello,

I am new to this list and I love working with the SX, however, I am having a problem with my current project. It is a fairly large project·that·reads inputs on 16 switches (using two cascaded 74HC165's) and has various outputs including an LCD·and LEDs.·For background information my project contains four boards and all components are soldered·to the boards. The four boards are mounted to a wooden board using standard standoffs etc.

Everything works great so as long as I don't bump my project at all. I can do nothing more than tap on the table where my project is sitting and·my SX seems to go into "La La Land". The best that I can·figure is that somehow by me tapping on the table causes anomilous·voltage levels·on the input/output pins. I am at a loss as to why this is happening. I did try switching out the SX chip with another chip and I still get the same thing.

Any ideas anyone? Is the SX chip really that sensitive?

Thanks.

-Dustin

·

Paul Baker

This is likely due to one of two problems. Either:

1) you have a connection which only makes an intermittant connection, you can test this by using a DMM at the source and destintation and wiggle any wires, if the resistance reading changes you found a bad connection.

2) you are not using pullup resistors, I personally experienced this problem. Sometimes it will behave properly if not using pullup resistors because of small amounts of charge injection on the wire when switching, but when you move the wire, the charge can leak due to changes in lead capacitance resulting changes in voltage level.

Chris Savage

My bet is on a loose connection somewhere.· Perhaps even a loose/cold solder joint.· Back when we used to repair computer monitors, we would frequently get ones in that had cold/loose solder joints on the flyback transformer, and vibration/tapping on the desk or monitor would really screw up the display.



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