Post by thread:PIC14000 and MPX5100A sensor

>> The external A/D converter is 12-bit; the internal, 8-bit. It's a >> question of granularity. Do you want your altimeter to register 256 >> separate Feet (Meters) or 4,096 separate Feet (Meters) of altitude? > >It looks like I'm either going to have to either use external >conditioning circuitry with the 8 bit 16C71 or an external (higher >accuracy) A/D with the 16C84. Thanks for the reply I'm also in the process of designing a PIC-based altimeter, requiring 12 bit or greater resolution at 1 sample/sec. It seems to me that this would be an ideal application for the 14000. However, the data sheet and application notes are a little vague on how to achieve optimal analog performance. AN624 mentions that "A [resistive voltage] divider that results in an A/D input voltage that is as near as possible to the bandgap reference voltage is normally selected, since it reduces ratiometric errors during the calculation of the voltage." The only indication of what the nominal bandgap reference voltage tends to be is in AN621, where 1.1842 [volts] is given as a typical value of the bandgap reference voltage calibration constant. Since the full-scale output voltage of a MPX5100A is 4.8 volts, this would imply that a voltage divider is, in fact, appropriate. Has anyone used the 14000 for similar applications? _____________________________ Marc Ramsey, spam_OUTmarcTakeThisOuTranlog.com http://www.ranlog.com/ramsey/

> I'm also in the process of designing a PIC-based altimeter, requiring 12 bit > or greater resolution at 1 sample/sec. It seems to me that this would be an > ideal application for the 14000. In one ap I'm doing where I need 12 bits A to D, I take a port pin output, run it through an RC filter, and then run that into a comparator along with the input signal. In my timer tick, I set that output port to match the input port and increment a count if it was "high"; every 4096 loops I store the count, zero it, and start again. Seems to work pretty well, though I don't get readings all that fast.

At 09:03 AM 11/14/96 -0800, you wrote: >>> The external A/D converter is 12-bit; the internal, 8-bit. It's a >>> question of granularity. Do you want your altimeter to register 256 >>> separate Feet (Meters) or 4,096 separate Feet (Meters) of altitude? >> >>It looks like I'm either going to have to either use external >>conditioning circuitry with the 8 bit 16C71 or an external (higher >>accuracy) A/D with the 16C84. Thanks for the reply > >I'm also in the process of designing a PIC-based altimeter, requiring 12 bit >or greater resolution at 1 sample/sec. It seems to me that this would be an >ideal application for the 14000. However, the data sheet and application notes >are a little vague on how to achieve optimal analog performance. AN624 >mentions >that "A [resistive voltage] divider that results in an A/D input voltage that is >as near as possible to the bandgap reference voltage is normally selected, since {Quote hidden}>it reduces ratiometric errors during the calculation of the voltage." The only >indication of what the nominal bandgap reference voltage tends to be is in >AN621, >where 1.1842 [volts] is given as a typical value of the bandgap reference >voltage >calibration constant. Since the full-scale output voltage of a MPX5100A is 4.8 >volts, this would imply that a voltage divider is, in fact, appropriate. > >Has anyone used the 14000 for similar applications? >_____________________________ >Marc Ramsey, .....marcKILLspam@spam@ranlog.com >http://www.ranlog.com/ramsey/ > > I am doing that exactly. I am building an altimeter (actually an autopilot, which includes an altimeter) with the PIC14000 and the MPX5100A. You are correct. A voltage divider is necessary to bring the full scale range to within 3.5V DC, max input for the PIC14000. I think the PIC14000 should be an ideal component for this application because the A/D converter in integral, and it is of the type that produces good accuracy (16 bits resolution, most of them accurate) albeit at a slow rate. Dewey Davis