Post by thread:Linear sensor input for PIC16F84

In message <spam_OUT610ad388.34b69691TakeThisOuTaol.com>, PHXSYS <.....PHXSYSKILLspam@spam@AOL.COM> writes >ello > >I need a very accurate linear position sensor, that can measure verticle >object travel of approx 1.5 inches. Cost is an issue. It will be an input for >a PIC16F84, so a digital signal would be less work. You haven't specified the accuracy you need! How about an arrangement using a rotary encoder with a gear/ratchet assembly? Or, adapt the technique used in digital calipers. I think that they use some type of low-cost capacitive sensor. Moire' fringing is an optical technique sometimes used for this type of application. Leon -- Leon Heller: leonKILLspamlfheller.demon.co.uk http://www.lfheller.demon.co.uk Amateur Radio Callsign G1HSM Tel: +44 (0) 118 947 1424 See http://www.lfheller.demon.co.uk/dds.htm for details of my AD9850 DDS system - schematic and software.

I need a very accurate linear position sensor, that can measure verticle object travel of approx 1.5 inches. Cost is an issue. It will be an input for a PIC16F84, so a digital signal would be less work. Can anyone help? Try this.... Mouse ball princable and a fixed sensor to check end of travel...... a slotted (laser etched) strip and a slotted opto switch with an additional switch opto or mechanical to indicate 'home' Alternatively if the mirco is controling the movement a single switch to signify end of travel and a steppermotor driving a worm gear to move the object sorting out the position is a matter of counting steps. Alternitivly read the thread on 'reading a pot without a-d and use a pot Just a couple of ideas.... Cheers Steve............

In message <.....610ad388.34b69691KILLspam.....aol.com> EraseMEPICLISTspam_OUTTakeThisOuTMITVMA.MIT.EDU writes: > ello > > I need a very accurate linear position sensor, that can measure verticle > object travel of approx 1.5 inches. Cost is an issue. It will be an input for > a PIC16F84, so a digital signal would be less work. > > Can anyone help? > Jon, Several methods come to mind some cheap, some not so: o LVDTs (not so cheap and will need external conditioning, but very reliable). o Slider POTS (cheap and can be directly interfaced to C84 as as recent thread has explored). o Sony MagnaScale (not so cheap, but with quad encoded output so direct connection to C84 is possible). There other methods which I'm sure others will mention. Regards, Mike Watson -- Denison Mayes Group

You could possibly take two low-cost ultrasonic transducers and mount one on a fixed base and the other on the sliding part, then pulse the transmitter and measure the delay to the receiver. From memory the speed of sound is approx 300m/s so 1.5 inches will provide a delay of around 100uS if my quick math is correct. This method is, however, sensitive to variations in temperature as the air density changes, but I don't know how significant this would be. {Quote hidden}> ---------- > From: XYGAX[SMTP:XYGAXspam_OUTAOL.COM] > Reply To: pic microcontroller discussion list > Sent: Saturday, January 10, 1998 9:37 PM > To: @spam@PICLISTKILLspamMITVMA.MIT.EDU > Subject: Re: Linear sensor input for PIC16F84 > > I need a very accurate linear position sensor, that can measure > verticle > object travel of approx 1.5 inches. Cost is an issue. It will be an > input for > a PIC16F84, so a digital signal would be less work. > > Can anyone help? > > Try this.... > Mouse ball princable and a fixed sensor to check end of travel...... > a slotted (laser etched) strip and a slotted opto switch with an > additional > switch opto or mechanical to indicate 'home' > Alternatively if the mirco is controling the movement a single switch > to > signify end of travel and a steppermotor driving a worm gear to move > the > object sorting out the position is a matter of counting steps. > Alternitivly read the thread on 'reading a pot without a-d and use a > pot > > Just a couple of ideas.... > > Cheers Steve............ >

Jon, I'd suggest using a 16C71/710/711/715 as they cost less than a 16x84 and they have up to 4 channels of A/D built-in. Then use a simple linear pot. Depending on the selection of the pot, you can get very good resolution. The best resolution usually comes from LVDTs but they are expensive and usually require a lot of analog `glue'. Optical-based sensors are another option but they are also more expensive, require more I/O, and like LVDTs, they require more software. I've seen a lot of discussion here about using a 16x84 for analog input. However, the above parts cost less, are pin compatible as well as software with the exception of the A/D configuration registers. If you only have a 16x84 programmer, then I'd recommend an external serial A/D or John Payson's suggestion of an R/C-based A/D. Personally, I'd avoid gears and magnetic tape ;-) - Tom At 04:28 PM 1/9/98 EST, you wrote: {Quote hidden}>ello > >I need a very accurate linear position sensor, that can measure verticle >object travel of approx 1.5 inches. Cost is an issue. It will be an input for >a PIC16F84, so a digital signal would be less work. > >Can anyone help? > >Thank you > >Jon Petty > >