Nick Howard wrote: >I need to build a heart rate monitor using light passing through a finger >being detected by a photodiode. The output should for preference be a >voltage pulse between 0V and a volt or two. Single rail operation would >also be an advantage. I have seen heart rate monitors on gym machines which had something like a crocodile clip(only less painful) which clipped on to your ear lobe. This may eliminate some of the problems which Bob Fehrenbach mentioned. Let me know how you go. I always wanted to build a PIC based circuit which will run on a battery and sit in my pocket. A cable from this device goes to my ear. It has two things on it - an earlobe clip and an earphone. When your pulse rate falls below or rises above a band different tones can be heard. This can be handy while excercising to help you keep your pulse rate at the appropriate aerobic level. Regards Prashant --------------------------------+--------------------------------- Prashant Bhandary | Tel: +61-2-9662 5299 Spatial Information Solutions | Fax: +61-2-9662 5348 Roads and Traffic Authority | Email: prashb@rta.nsw.gov.au Rosebery NSW 2018, AUSTRALIA | "2b|!2b" - William Shakespeare --------------------------------+---------------------------------