LogicBlocks Experiment Guide
jimblom 
2. 3-Input AND Gate
Sometimes you need to AND more than two inputs together. In fact, 3- and 4-input AND gates are just as common as the dual-input variety. Let’s make a 3-input AND gate out of two two-input AND gates.
What You'll Need
- 3x Input Blocks
- 2x AND Blocks
- 1x Power Block
Circuit diagram
LogicBlock layout
Start by building the 2-input AND block from the last experiment, but plug the output of that into the input of another AND. Then add an Input Block to the second AND's second input.
Complete the circuit by adding a Power Block to the output of the second AND.
The blue LED on the second AND gate represents the output of this circuit.
The Experiment
With three total inputs, how many different input combinations can you make? 8! This number grows exponentially at 2n, where n is the number of inputs. So, a 4-input AND gate has 16 possible combinations, 5 inputs would be 32 outputs, and so on.
Try all possible input combinations and fill out the truth table below:
| Input A | Input B | Input C | Output Y |
|---|---|---|---|
| 0 | 0 | 0 | |
| 0 | 0 | 1 | |
| 0 | 1 | 0 | |
| 0 | 1 | 1 | |
| 1 | 0 | 0 | |
| 1 | 0 | 1 | |
| 1 | 1 | 0 | |
| 1 | 1 | 1 |
- Can you think of a situation in real life where three requirements must be met before an outcome becomes true?
- If you had more AND blocks, can you imagine what a 4-input AND block might look like?
Sub-Experiments
Try using two OR gates and three Input Blocks to create a 3-input OR gate.
- Draw a schematic diagram for this circuit.
- Write out a truth table for this circuit. Like the 3-input AND circuit, this circuit will have 8 possible sets of input. But there should be a lot more 1's on the output column!