This adapter (published in Silicon Chip
Magazine) will enable the measurement of low resistance with your
digital multimeter. Unfortunately the method I designed for connecting
to the multimeter was not described.
An alkaline battery and theLM317
connected as shown provides a constant 100mA through the resistor to be
tested and your digital multimeter measures the voltage across it. A 2
volt range will measure to 20 ohms and a 200 mV range to 2 ohms.
Construction could consist of fixing the LM317
inside a small box and soldering the resistors to its legs. No current
is drawn when the leeds are disconnected so if they are properly
insulated no switch is required. The screw on probe connectors are made
by sawing a screw section from a 2 screw terminal strip. A lead is
soldered to the bottom of the connector then heat shrink is pushed over
it. The heat shrink provides strain relief for the lead and shrouds the
To attach a meter probe push it through the heat
shrink and do up the screw. Accuracy using 1% resistors should be
within 5% and is aided by the test current not having to pass through
the multimeter leads.
The resistance of the current carrying leeds and
the contact resistance of the screw connectors is compensated for
For greater accuracy the current could be
measured and a correction factor noted or the resistor values selected
for exactly 100mA.
Before using check that the meter will not be
harmed by the full battery voltage being impressed on the low voltage
ranges you intend to use and be aware that the current and voltage that
the adapter outputs could damage susceptible components in a circuit