Count-Down Timer - Relay Output Switch

Since timer kits are extremely in hobby kit builder circles - we just had to satisfy the urge of the community! The 555 timer IC is perhaps the single most popular way of making timer circuits - so we used that too!

This circuit uses the 555 counter IC as the timer, and two transistors in order to switch the relay-switch to either ON or OFF, depending on a user-selected jumper setting. There are also jumpers which all the constructor to select the the countdown time value - from 8 - 8192 seconds (about 2 hours 15 minutes).

The circuit primarily consists of 3 parts: an oscillator, a ripple counter and two switching transistors.

Specifications:

• L: 2" W: 2-1/4" H: 5/8"
• Requires external 12 volt dc power supply
• Jumper Selectable count down times ( 8 to 8192 seconds)