> Any ideas on a simple (and cheap) method of detecting whether > motion is left-right or right-left so I can invert the message as > appropriate. 2 mecury switches mounted in some way so that the > leading edge triggered first seems the obvious solution but how to > actually implement this? Not so simple and cheap: use an accelerometer chip. Positive and negative acceleration. Everyday Practical Electronics recently ran an article using one of these. I liked the calibration - tip it up one way = +1g, tip it up the other = -1g. Pure conjecture: Simple and cheap - use 2 mercury switches mounted 90 degrees from each other (and 45 degrees from vertical) so that acceleration in one direction opens one, accel in the other opens t'other... Dodgy ASCII art: \/ Contacts at base; mercury at rest -> no motion. Accel to right -> right hand switch closed, left hand switch open. Accel to left -> left hand switch close, right hand switch open. Probably with lots of debouncing to make sure that slightly off-axis movement doesn't really upset things. HTH Peter -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.