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Circuit 134: NOR gate with moving-coil instrument
Setup information
Install the two transistors, the two diodes and the two resistors as shown in Fig. 2.134. The four jumper
wires come next followed by the jumpers, which serve as switches (shown dashed). For your guidance we
have labelled the switches with high E1 and high E2. Last but not least connect the moving-coil instrument.
Check the placement on the board again and only then connect the battery.
Experiment
Even if everything is wired correctly, nothing will happen at first. Both "switches" are open, the needle of
the moving-coil meter is not moving. The potential at the output is high. The following table, also called
truth table, shows what will happen now at the different switch states.
Input 1
low
high
low
high
Input 2
low
low
high
high
Output
high
low
low
low
Components required:
2 x 2N3904 transis-
tors, 2 x 1N4148 silicon
diodes, 1 x 4.7 kΩ resis-
tor, 1 x 10 kΩ resistor,
1 x moving-coil instru-
ment, 1 x breadboard,
1 x 9V battery with clip
connector
Fig. 2.134: NOR gate with
moving-coil instrument
Moving-coil instrument
no motion
full-scale
full-scale
full-scale
159
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