How to wire a 74HCT02 (NOR-gate)

integrated-circuitlogic-gates

I'm trying to make a logical NOR-gate using a 74HCT02 IC (datasheet), but I cannot figure out how to wire it. Below is a schematic of what I tried.

schematic

^{simulate this circuit – Schematic created using CircuitLab}

The power source (V1) is coming from a transformer connected to the power net, it gives a 4.5 VDC output at 3.6VA maximum.

What I observe is that the led is always on, with little intensity difference when I press or release either button.

I do not have much experience regarding circuits with IC's, so I might be making some beginners mistakes here.

Best Answer

As drawn, your inputs to the gate will always be low. The resistors R2 and R3 pull it low (to ground/the negative side of the supply). Then when you push the switches they connect the inputs to low again, so they have no effect. Rewire the switches so when you push them they connect the inputs to the high side of the supply, that way you will get low until you push the switch, then they will override the resistors and provide high.

Related Solutions

Electronic – Uses for gate expressions, Nor and Xor

Truth tables:

NOR (NOT-OR) is more or less like NAND:

0 NOR 0 = NOT(0 OR 0) = NOT(0) = 1
0 NOR 1 = NOT(0 OR 1) = NOT(1) = 0
1 NOR 0 = NOT(1 OR 0) = NOT(1) = 0
1 NOR 1 = NOT(1 OR 1) = NOT(1) = 0

XOR emits 1 when the two inputs differ. You can consider this as binary addition without carry.

A XOR B = (NOT(A) AND B) OR (A AND NOT(B))

0 XOR 0 = 0
0 XOR 1 = 1
1 XOR 0 = 1
1 XOR 1 = 0

Boolean expression to NOR gate (MUX)

A=input 1, B=input 2, S=switch
from A create A' (nor port with 2 times A as input)
from B create B' (nor port with 2 times B as input)
from S create S' (nor port with 2 times S as input)
create X=(S+A')' (nor port with A' as input and S as input)
create Y=(S'+B')' (nor port with B' as input and S' as input)
create Z=(X+Y)'=((S+A')'+(S'+B')')'
create W=Z' (nor port with 2 times Z as input)
then W=(((S+A')'+(S'+B')')')'=((S'.A)+(S.B))''=S'.A+S.B

Best Answer

Related Solutions

Electronic – Uses for gate expressions, Nor and Xor

Boolean expression to NOR gate (MUX)

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