You don't need a seperate chip to store data on, if your using any of the PIC's that are flashable, as they have EEPROM onboard. There are even some really cheap 8 pin OTP's (One Time Programmable, with onboard ADC) chips that have EEPROM on board (they are limit to 4 byte stack space however). Just throw the chip back into your programmer after flight, and read the EEPROM to get the data. There is usually enough EEPROM, where you could have it record a new value to anothor EEPROM location once every 1 or 1/2 second after launch (tie a pin to your battery ignition starter, and have it start logging when you send power to it to lanch). Maybe check out MicroChip's line card again, and look at the features of what each chip offers. -----Original Message----- From: Tony Goetz To: PICLIST@MITVMA.MIT.EDU Date: Saturday, December 30, 2000 6:23 PM Subject: [PIC]: Use in a rocket altimeter >Hey all, > >Right off, I'm a beginner to PICs. The only microcontroller programming I've >done before now has been with a Ti-83 graphing calculator, if that can be >considered uC programming, but I have written programs in C++ for computers. > >That said, my first project using a PIC will be an altimeter for model >rockets. A friend of mine got into rocketry and mentioned wanting to know the >altitude of his rocket without expensive electronics and I said it could >probably be done with a PIC, a pressure sensor, and if he didn't want to mess >with wireless stuff, a memory chip to hold the data. I'd like to write this >in C, if possible, but will use assembly if I have to. Which free C compiler >out there would you recommend? > >After exploring how to go about doing this, I have a pretty good idea on what >to use. The friend got ahold of a Motorola Mpx4115 pressure transducer from >his work and its datasheet (so simple, *I* might even be able to figure it >out!) and I found a site where a guy used one to build his own telemetry >system using a transmitter, which gave me insight on what techniques could be >used. Basically my circuit will take the analog output of the Mpx, and modify >the voltage using op-amps so that from a range of 101kPa to 69kPa (0-10000 >feet) the output will vary from about 0-5v. This will go through an ADC, the >altitude will be calculated by the PIC, and this value put on a chip. > >My questions: I want the ADC to be 12-bit. If I use the converter built into >some PICs, I'd have to use a Pic16C773 or 774 to get this resolution. Should >I bother buying one of these and trying to figure out how to program it or >should I use an external ADC with a 16f84 (or similar)? Also, would an EEPROM >be a good idea for storing the results in this application, or should I go >with something else? An important part- when I get the converted output into >the PIC, I still need to do some calculations. I figured out a good equation >that is accurate +/- 2.5ft from 0-10000ft, but uses long coefficients (the >equation is at the bottom). Can the PIC handle this well, and can it do it 8 >to 16 times per second or should I have it simply save the raw ADC value to >be computed on the ground? Finally, does the general idea sound doable? > >Thanks in advance and sorry for writing a long, rambling letter. I tend to go >into detail when I write......... > >-Tony > >F(x) = -.01400624739751 * P^3 + 5.4327443467593 * P^2 + -928.47534934054 * P >+ 52868.578588933 >where X=altitude in feet and P = atmospheric pressure in kPa > >-- >http://www.piclist.com hint: The PICList is archived three different >ways. See http://www.piclist.com/#archives for details. > > > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body