Instructions

158
2.62 NOR gate
Circuit 133: NOR gate with LED
Setup information
Install the two transistors, the three diodes and the two resistors as shown in Fig. 2.133. The six four jumper
wires come next followed by the jumpers, which serves as a switch (shown dashed). For your guidance we
have labelled the switches with high E1 and high E2 Check the placement on the board again and only
then connect the battery.
Components required:
2 x 2N3904 transistors,
2 x 1N4148 silicon diodes,
1 x red LED,
1 x 1 kΩ resistor, 1 x 10 kΩ
resistor, 1 x breadboard,
1 x 9V battery with clip
connector
Fig. 2.133: NOR gate with LED
Experiment
Even if everything is wired correctly, nothing will happen at first. Both “switches” are open, the LED is off.
The potential at the exit is high. The following table, also called truth table, shows what will happen now at
the different switch states.
Input 1 Input 2 Output LED
low low high dark
high low low illuminated
low high low illuminated
high high low illuminated
The high state of the inputs is caused by closing the respective switch. If the switch is open, the input is
low. Such a circuit with the behaviour described above is known in digital electronics as NOR gate. A tablet
or notebook PC contains tens of thousands of those gates.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.133.