You can run them backwards.=20 Spehro wrote: > >! > >On 2012-10-11, at 9:47 AM, Brendan Gillatt = wrote: > >> On 11 October 2012 00:27, M.L. wrote: >>> A while back there was discussion of non-volatile displays. I found >>> one that nobody thought of: >>> The Mercury Coulometer >>>=20 >>> An obscure, antique, highly toxic device that has a glass tube, two >>> electrodes, and two columns of mercury separated by a liquid >>> electrolyte. >>> Electrical current passing through the device transfers mercury from >>> one side of the electrolyte bubble to the other, creating a linear >>> indicator - albeit very very slow, fragile, toxic, etc. >>>=20 >>> See the diagram at the end of this paper for a clearer picture: >>> http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19700023619_197002= 3619.pdf >>>=20 >>=20 >> I actually own one of those devices! It is packaged in a form similar >> to a large, glass bodied fuse with wires soldered to both ends. A >> graduated paper scale sits behind the mercury column to mark time >> intervals. Until now I've not known the name of the device, let alone >> how to drive it. > >I've got one as well, in an old (1970's) Tek dual-beam storage oscilloscop= e! >Something like 0-5000 hours. > >--sp > > > >--=20 >http://www.piclist.com PIC/SX FAQ & list archive >View/change your membership 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 .