At 09:43 PM 1/20/2008, alan smith wrote: >This is a pick your brain question. I've got a design, where I have >a single turn pot being used to set a overload value for a current >monitor. Its in a moving vehical, so my first thought was to just >set it up once, then forget it. But im thinking I may want to be >able to adjust it at anytime and read it while the unit is in normal >operation. So how much variation in the pot might I see after its >bounced around for a while? Good quality trimpots are surprisingly stable - AFTER they have settled. In other words, they might change value slightly after being changed, then subjected to vibration. I generally deal with that problem by tapping the trimpot after changing it, then resetting to the desired value. Repeat as necessary. However, do you have other environmental issues besides vibration? I'm currently working on 2 different projects that will be subject to trace amounts of Hydrogen Sulfide (H2S). I've convinced the customer NOT to use trimpots, but rather, use buttons and watch blinky LEDs. The idea is that even if the buttons fail, that doesn't matter because any values subject to change are already set and stored in eeprom. Trace amounts of H2S, even at very infrequent intervals, tend to render most trimpots useless after a number of years. Note that you can read a pushbutton and drive a LED from a single pin using just resistors (no diodes). A little more work lets you read 2 or more buttons plus drive a LED from 1 pin. However, my current projects use 2 pins = 2 buttons plus 2 LEDs. The other neat trick I'm doing is that one of the LEDs is actually spitting out a serial bit stream while it is lit. This allows me to have a hand-held device with a LCD display showing an actual menu structure. The same 2 buttons on the card allow navigating the menu and setting values. It also allows reading stored events that have been written to eeprom (failure modes, mostly). Basic settings can still be changed using just the buttons and watching the blinky LEDs. dwayne -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist