why do we require transistor switches ........I read one related forum in that it was written transistor switches can be triggered using electrical signals. TRUE.but if at all u want to off the ckt give zero signal(may be through microproccesor) to the o/p directly why do you want to increase your hardware for that? and when when you want current at o/p give the current directly.anyway we can programme our μp. so why transistors????????