Thanks for the help folks. I'm afaid Marks that your circuit uses devices not readily available to me and is alittle more complex than I wanted - many thanks for your trouble however. Ardhuru -- looked at the site you suggested but can't relate it to my problem ... thanks anyway. I have tried to approach the problem another way i.e. to use the sleep command to minimise power consumtion. Im still having problemas however (brain ain't what it used to be) hence a new post related to interrrupts which I am about to submit.