> My problem is this: I need to be able to toggle power on and off through > a waterproof membrane. It's a bit flexible, but not enough to allow a > standard push on-off type switch. I was thinking about using a small > tactile momentary switch and an SCR, but I don't think I can get that to > work. The problem is getting a normally closed tactile to act as the > "off" switch. This is a one off, of course. > > So here are my specs. I need a power switch/controller type of circuit > that can be turned on and off using small normally open tactile switch, > or two switches, that would be fine too. Size, power consumption, and > ease of construction would also be factors. I would prefer to not have > to order some esotheric switch from elsewhere. It sounds like the best method is to have a low power PIC always on but mostly sleeping sensing something accross the membrane. It could even wake up every 50mS to check for a condition and still keep the current draw to negligible levels. So the question now becomes what kind of information can you pass accross the membrane easily. There are a limitless number of hairbrain schemes, as I'm sure will be suggested over the next day. Here are just a few: Microswitch, or other low-travel momemtary mechanical switch. I use Jameco 119010 for "jelly bean" el-cheapo momentary pushbuttons. These have a very short travel and might work directly. You didn't specify what the acceptable deviation of your membrane is. Some sort of capacitive coupling sensor kludge detecting the presence of your finger. An externally generated AC voltage capacitively coupled. An externally generated magnetic signal. Light. The PIC wakes up every 50mS to power up and check a photodetector. I won't even get into various motion sensing schemes. I the end, the best system is obviously connecting your gizmo to the level sensor in a small tank. Fill the tank for on, drain it for off, see archives for details . ***************************************************************** Embed Inc, embedded system specialists in Littleton Massachusetts (978) 742-9014, http://www.embedinc.com -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu