This 1969 Mullar circuit appears elsewhere on this site. The circuit uses germanium diodes and the indicator is microammeter with zero in the center of the scale.
This circuit is based on a Texas Instruments LinMOS integrated circuit consisting of an...
This sophisticated logic probe for 5 to 12 V circuits (CMOS and TTL) was found in a 1980s...
This 2005 Linear Technology circuit has separate outputs for monitoring the charge and discharge...