This is a design circuit that has same with design in the last version. This circuit is an alternative when it is powered from the same battery as it monitors for current, this kind of meter requires a dual power supply with common-mode input voltage well between the supply voltages. This is the figure of the circuit.
The negative supply is easily provided, using a 7905 to provide -5V relative to voltage (1), the Load. A positive supply relative to voltage (1), the Load, requires addition of a voltage pump. One was made based on an NE555 IC running as an astable, the output of which was rectified to pump up a capacitor to a positive voltage. While this worked, there was a non-zero reading when the inputs were shorted: this could not be resolved for quite a while. It turns out that I had made a fundamental error of precision metering, namely the meter was drawing current from one of the sensor wires and the impedance of that wire is sufficient to cause a voltage drop of a couple of milli volts - the observed offset.
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