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Project #323
OBJECTIVE: To build a 1mA meter circuit.
1mA Meter
Project #324
OBJECTIVE: To build a voltmeter.
0-3V Voltmeter
Build this 0-3V voltmeter circuit. Using new batteries, place the battery
holder between points A & B. Adjust the variable resistor (RV) so the
meter deflects full scale.
Now you can check your other “AA” batteries by inserting them into the
battery holder.
Inside the meter (M2), there is a fixed magnet and a moveable coil
around it. As current flows through the coil, it creates a magnetic field.
The interaction of the two magnetic fields cause the coil (connected to
the pointer) to move (deflect). By itself, the meter can measure 300µA
or 0.3V. To increase its range, resistors are connected in parallel or
in series to the meter.
Build the circuit shown. Placing the 100Ω resistor (R1) in parallel with
the meter increases the range to 1mA. More current flows through the
resistor than the meter. The lower the resistor value, the wider the
range of the meter.
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