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EDIT 24 Oct 2018  The schematic in this post contains an error.  It will be reposted after receipt of the PCB and testing.   I am developing an inexpensive but reasonably accurate meter for measuring resistance in the milliohm range.  The previous posts are listed in the related links at the bottom.  In this post the design for the working prototype is expanded to include a second current source for measuring resistance up to 400 ohm and provision made for future auto-r ...
I am developing an inexpensive but reasonably accurate meter for measuring resistance in the milliohm range.  The three previous posts are listed in the related links at the bottom of this post.  In this post a working prototype is presented that has milliohm accuracy down to one millivolt.  A schematic and test data are presented along with plans for the next steps.   Current Status That heading above is supposed to be a pun :-).  Much of the work since the last post ...
Introduction This is the third post on the development of an inexpensive but reasonably accurate meter for measuring resistance in the milliohm range. In the first post a simple current source was described that created a 10 mA current  across a resistor that allowed the voltage drop to be measured using a multimeter and the resistance calculated.  A number of helpful suggestions were received and I ordered additional components based on that feedback.  In the second post a block ...