Hi Mike,I would like to know if you could supply some suggestions to help with the following problem if have.I run IO cards Servo board which can handle 4 analogue inputs and sixservos.They use a 16c745 pic which uses the supply for Vref for the A/D.My problem is that when connecting a pot(i want to use 5 turn ww pot)for trim control i find the output is not very stable.I find the trim postion servo chatters at the same time as the trim wheel in FSstutters.Iv looked at the output to FS and last digit from the a/dvaries.If i replace the pot with a fixed resistor divider this instability virtually dissappears.Iv been told by IO Cards peoplethat this is normal and is caused by the pot im using.Suggestedusing a more expensive one.Ive tried various ones but to no avail.Can you tell me what i should be looking for in the spec sheet to have minimal instability.Or am i not able to get this stability.I have assigned the slider on my joystick for elevator trim and connected up my servo to servo bd and all is nice and stable.So myservo bd is capable of stable operation.But finding a suitable pot is a big problem.I tried bypassing the data input to the pic with 0.1mfd caps but it didnt make any diff.Hoe you can help me out.Thanks for reading thisLes

Hi Les,I am woefully ignorant wrt IOcards. I do know that the ADCs on some microcontrollers are subject to source impedance issues on their inputs. One possibility is that the inductive nature of your wire wound pot is a problem. Do you see the same instability if you replace the ww pot with a non-ww unit while leaving everything else the same? (Same wiring, same resistance value for the replacement pot, etc.)Mikewww.mikesflightdeck.comwww.mikesflightdeckbooks.com

Hi Mike,Thanks for the comments.Yes i have tried a 5k ordinary carbon pot.The results are the same.Even the IOcards support people say that with good quality pots this oscillation occurs.So it looks like i will have to revert back to Rotary encoder.5 turn pot would have been really realistic as the true trim controls have 5 turns end to end.I checked this stability when i configured the slider from the joystick and find MS increments in 210 blocks as against single unitswhen config thru a/d.If i didnt want to read position with a servo,it would not worry me.Thanks for your comments,if any bright ideas pop up i would be glad to hear them.Best RgdsLesP.S Ive been following your thoughts re the new book.Any idea when we may be able to buy.Looking forward to it.The first one was greatinspirational material.

The manuscript for the next book, Building Recreational Flight Simulators, is at 514 pages with 608 planned. Several full time months of work remain, but I only get to work on it now and then. My estimates of publication dates have been outrageously bad, so I won't try to make another. Nonetheless, progress does happen, if slowly. I post book status info here: http://www.mikesflightdeck.com/upcoming_book.htmMikewww.mikesflightdeck.comwww.mikesflightdeckbooks.com

Hi Mike,Further to the above,i came across this device while looking for hall efect rotary sensors.After reading your latest imfo.Its a Vishay Smart sensor 360 degree continuous rotation.Linearity 1%.Price of theses are only $6 at mouser.Do you thinkthese would be much more stable than a pot.The Vishay part Number is Model 601-1045.Be very interested in your comments when you have time.Thanksles

Hi Les,That's a nice looking sensor, but i can't say if it would work better than a potentiometer with your interface card. There are far too many variables. USB devices power themselves up and down, the wiring presents unknown capacitance to the circuit, and so on.The price now appears to be $60.34 in unit quantities.Mikewww.mikesflightdeck.comwww.mikesflightdeckbooks.com

Thanks Mike,Point taken,i think i must have been optimistic when i said $6.will just use a rotary.Rgdsles