Safety Alarm Clock

Step 7 Transistorise

Transistors are great at controlling a large current by a small current. In this case I will use an NPN transistor to allow current to pass to a buzzer when the clock is unplugged.

Under normal conditions the current drawn by the clock is insufficient to allow any current to flow C to E and so the buzzer is silent.

When 2.3mA is drawn by the clock, the circuit is effectively opened between C and E, and so the buzzer can sound!

Comments

[jvpernis]

So when you unplug the clock the buzzer goes off alarming you that the clock has been unplugged or when you unplug the clock the buzzer goes off when he has to, just like when the clock is plugged? This is a very awesome idea!