Put all switches in the “in” position.
This will place all of the potentiometers
in the circuit. Now, adjust the leftmost
(one meg) pot until you get the desired
result. If your circuit needs less
resistance, put the one meg switch in
the “out” position (eliminating the one
meg pot). Now, adjust the 100K pot
until the desired result is achieved.
Again, if the resistance is still too much,
put the next (10K pot) switch in the out
Keep repeating this procedure until
you get the desired result. Once this is
achieved, disconnect the clip leads from
your project and place them across a
digital meter (set to read resistance).
Read the value, then look up that value
in a chart of standard resistor values.
Table 1 shows an example chart.
Get the closest standard EIA (Electronic Industries
Association) value and put this in your circuit. If a standard
value isn’t close enough, use combinations of series or
parallel resistors to get there. In some cases, a
potentiometer can be substituted for the value and
adjusted to get the exact match.
So, build the box, and have an accurate variable
resistance available to help your designs. NV
April 2014 37
; Box with meter attached.
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