Hello all, I'm a freshman electrical engineering student at the University of Kentucky. I'm also a DJ at our all-volunteer student radio station. I was browsing around the awe-inspiring project blinkenlights site and recalled the quasi-famous Green Building VU meter hack at MIT. Now on our campus we have a convienently tall building atop which sits our transmission tower. I'm toying with the idea of doing a large installation for some special event for which that building is turned into a very large VU meter (showing the volume of our broadcast). Now, this building is habitated so we don't have the luxury of running wires from floor to floor (even if we wanted to). My idea was to get 10 or so radios (one on each floor), tune them to our station, and send their outputs to a circuit that turns a light on ad off. Make the set up more sensitive on each successive floor as you go down (either by adjusting the comparator reference or the radio volume) and you get nicely synchronized lights (we are in control of the transmission, so we could broadcast some calibration signals to aid the process). I figure the circuit will consist of nothing more than a relay and comparator. The radio (hopefully found cheap and in bulk on ebay) output is connected to the input of a comparator, and the comparator output is connected to a SPST-NO (single pole, single throw, normally open) relay (like this one). My present problem is that I can't seem to find a comparator IC that can supply enough current for the relay coil (200mA in the example relay given above). Should I use a transistor? Am I just really bad a searching for comparators? I'd prefer the comparator supply voltage to be something for which wall-warts are widely available and radios are likely to run on (to avoid multiple power supplies). 5 to 9 volts or so. So is my approach at all sensible? I'm eager to order parts for a prototype, but I'd hate to do it without a basic sanity check.