:: Thanks to all that replied... I'm going to have to figure out if :: I want to tackle the ultrasonics - they are very interesting indeed Way back in the late 90's or early 00's the UK magazine Practical and=20 Everyday Electronics (EPE magazine) did a 2 part ultrasonic wind speed=20 project. www.epemag.com www.epemag.co.uk Colin -- cdb, colin@btech-online.co.uk on 26/03/2011 =20 Web presence: www.btech-online.co.uk =20 =20 Hosted by: www.justhost.com.au =20 =20 =20 =20 =20 --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .