Roland Andrag > I am in the process of building an altimeter using a PIC and the > MPX5100A sensor, which is very well suited due to the fact that it is > fully temperature compensated. Is there any reason for using an > external A/D converter instead of using something like the PIC16C71 > which has a four channel 8-bit A/D built in (besides the '84 EEPROM vs >'71 EPROM)?? As someone who is also using the MPX5100A sensor in Variometer product that I built for Paragliding and Hangliding enthuisiasts, I feel that that I also ought to say my little bit here... :) My vario uses a PIC16C71 with some analog circuitry to condition the signal before it goes to the the AtoD. You will find that without this analog circuitry, the 8 bit A/D of the 16C71 would not provide sufficient resolution and sensitivity. However, if you want to use some higher resolution external A/D's like the MAX195 which is a serial I2C 16 bit A/D, then you can probably do away with any external analog circuitry and still have exceptional accuracy. So I agree with Roland, I would also go for an external A/D, unless cost is a big issue. Another popular technique would of course be to use the technique of converting the analogue signal to a frequency using a voltage to frequency converter and measuring this frequency. This is generally less expensive than external A/D, but with additional problems such as temperature compensation and measuring range problems. Regards Werner -- Werner Terreblanche Tel +27 21 7102251 Fax +27 21 721278 wterreb@plessey.co.za (work) OR werner@aztec.co.za (home)