<< I've not been following this thread so forgive me if this has already been posted.... I found this link, having a simple PIC based rocket altimeter and other neat rocket projects... http://www.tfs.net/~petek/projects.html He uses a MPX4115 pressure sensor and also includes some op-amp signal conditioning circuitry to increase the accuracy of the measurement. I plan to build a similar circuit but with a 16F877, which has an on-board 12 bit A/D converter. Hope this is useful to you. Freddie. >> It hadn't been posted, but that's actually the site I found. I would use the 16F877 too, but it has a 10 bit ADC, not 12. 10 would be good enough for this, providing around 10 foot resolution 0-10k feet, but 12 would be better still, providing around 2.5 feet res. Supposedly the Mpx is sensitive enough to detect a change in pressure between your head and your feet. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body