The Space Station Airlock
To open the AIRLOCK, both the PRESS and TEMP sensors must signal safety, but only if the LOCK lever is not engaged. The ALARM sounds if the TEMP sensor is high while either PRESS or LOCK are active.
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The truth table
Inputs on the left, outputs on the right. A circuit solves the puzzle when it reproduces every row.
| PRESS | TEMP | LOCK | AIRLOC | ALARM |
|---|---|---|---|---|
| 0 | 0 | 0 | 0 | 0 |
| 0 | 0 | 1 | 0 | 0 |
| 0 | 1 | 0 | 0 | 0 |
| 0 | 1 | 1 | 0 | 1 |
| 1 | 0 | 0 | 1 | 0 |
| 1 | 0 | 1 | 0 | 0 |
| 1 | 1 | 0 | 0 | 1 |
| 1 | 1 | 1 | 0 | 1 |
What the table tells you
- AIRLOC is 1 in 1 of the 8 rows, so it is a single AND-shaped condition: one exact combination of the inputs. Every input matters: for each one there is a row where flipping it changes AIRLOC. The rows that turn it on: PRESS=1, TEMP=0, LOCK=0.
- ALARM is 1 in 3 of the 8 rows. Every input matters: for each one there is a row where flipping it changes ALARM. The rows that turn it on: PRESS=0, TEMP=1, LOCK=1; PRESS=1, TEMP=1, LOCK=0; PRESS=1, TEMP=1, LOCK=1.
The smallest known circuit: 5 gates
As a formula, one line per output:
AIRLOC = ((PRESS AND NOT TEMP) AND NOT LOCK)ALARM = (TEMP AND (PRESS OR LOCK))
As a netlist, in the order you would wire it. Each g is one gate; the last lines say which signal drives each output.
g1 = PRESS AND TEMPg2 = LOCK OR g1g3 = NOT g2g4 = TEMP AND g2g5 = PRESS AND g3AIRLOC = g5ALARM = g4
The search checked every circuit with fewer gates and none matches the table, so 5 is the true minimum for the allowed gate set. Gates that do not feed an output are never counted.
Leaderboard for the day
Nobody posted a result on the day. The circuit above is the reference.