Take the micro meter case apart and drill/cut a hole in the side of
the lower case on the side between the source and load wire slots and install a small two
position switch with three pins. Orient the circuit board with the LCD display down so the
long copper bar is at the top, and the plastic case has the switch at the bottom (see diagram
and first picture).
Solder the black wire from a Radio Shack 9V transistor battery pigtail onto the puddle of
solder at the left end of the copper bar (see arrow in second picture). A 9V transistor
battery will plug into this to power the micro meter.
Solder the red wire from the transistor battery pigtail to the left pin on the switch.
Locate the diode near the right end of the copper bar (see circled area in third photo
and diagram). snip off the right end of the diode — leaving enough sticking up
from circuit board to solder a wire to (you could also heat it with an iron and slide the
right end out of the circuit board).
Solder a length of red wire from the middle switch pin to the end of the diode that is
now not connected to the circuit board.
Solder a length of red wire from the right switch pin to the diode wire that is
sticking up from the circuit board.
With the case assembled, the micro meter will read zero when it is connected to a 9V
transistor battery, which is the auxiliary power source. Plug a NiCd or other battery to the
regular source wires and it will measure slightly more accurately because the meter is now
consuming no power. The meter can now measure below its normal operating minimum of 4 volts.
This is useful for micro planes which might have only two or three cells, or from a four-cell
pack near the end of a motor run when the voltage has dropped below 4 volts. With the switch
in the other position, the meter functions normally and does not need the 9V battery.
Bob Bucher’s great micro meter is now a bit better.
