On Tue, 29 Jan 2008 14:44:22 -0500 "Don Rahmlow" wrote: > This is a repost, I omitted subject yesterday... > > I'm experimenting with analog switches/muxes ('4051 and '4066)--my first > time. When selected, the resistance of all switches is as expected, <150 > ohms, but when control signal is low R varies from 20-50K among > channels, always way lower than spec. If power removed, all channels' > resistance is in spec. Well, resistance in integrated circuits varies depending on many factors. Measured channel isolation depends on the voltage difference you apply, for example. If your R measuremente uses varios volts, it is quite possible you are activating the input/output protection diodes. Also, if the 'common mode' voltage at which you measure, isn't at the center of VCC-to-VSS you'll meaure something different. Also note that those 4051 have a separate GND from VSS. They must both be connected. If I recall right, isolation is measured originally by inserting an AC signal in one channel, and measuring the effect on another, with that channel terminated with a impedance to ground. John -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist