All of which reminds me of this wonderful sketch.... http://www.youtube.com/watch?v=3DL7L3iSZsNpY Joe -----Original Message----- From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of= Martin McCormick Sent: 29 November 2012 19:22 To: Microcontroller discussion list - Public. Subject: Re: [EE] Constant Current Source for LED "Harold Hallikainen" writes: > Ahhh! Very fancy! My doorbell (electromechanical) stops when they let=20 > go of the button. My father lives across the street from us and his hearing is not what it o= nce was so we bought the electronic chime because it is LOUD! when you turn= the volume pot all the way up. An amusing thing happened when I first tried to connect the new bell. All = it would do was stutter on the first note but I could connect it up to the = transformer with alligator clips and, as long as the diode was supplying th= e half-wave DC, it worked just as it should. My wife was also in the house near the back door and said that she could h= ear this "clunk-clunk" sound each time I tried to hook the bell up. I knew = there was something else in the circuit but that helped a lot and a look ou= t the back door showed yet another door bell of the electromechanical type = over the back door. The previous owner of the house had had a second bell i= nstalled in parallel with the first one so the electronic bell did not get = along with the inductance and load of the outdoor bell. The outdoor bell was never meant for outdoor use and the rubber fasteners = had deteriorated over time and allowed both chime bars to fall off their po= sts. One clattered to the pavement as soon as I popped the cover off the bo= x. Had my wife not heard the solenoids in that defunct outdoor bell, I woul= d have probably ruined the bell transformer since that diode across the but= ton would have fed DC to the old bell and drawn a lot of current. Removing = the old bell made the new one ring forth for all to hear. My father can hear it but can't when he is watching television with headph= ones so I am working on an alert that will blink a light and maybe put a be= ep in the headphones when someone pushes the button. Martin -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membershi= p options at http://mailman.mit.edu/mailman/listinfo/piclist --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .