Introduction: Automatic Mailbox Light
I have been the last few days in transistor heaven. The mailman brought me tilt switches from China, so why not make some use of them!
In the house I live, the mailboxes are in a quite dark place. I made this light so that it will illuminate the inside of the box, helping to see the mail in dark. The features are fading in/out the LED:s and using tilt switch to turn the circuit on and off. The standby current of the circuit is 0 mA.
Step 1: Circuit
The circuit consists of a transistor that turns the LED:s on and off, a delay circuit that makes the LED:s fade in/out, tilt switch to allow power from batteries to circuit and a step-up converter that converts the battery voltage to 5 V. The boost converter can boost from as low as 0,2 V. This is pretty good because the system is powered by 1,5V AA batteries.
Step 2: Schematic
The schematic is a basic transistor switch with added fading effect. Fading in is made by charging the capacitor through R1. Fading out happens through R2.
Battery is two AA batteries in parallel (1,5V). I chose to put them in parallel because then it is easier to change them. If you have only one fresh battery the circuit will work with it, but only half as long as with two batteries.
When tilt switch is off, the batteries are not connected to anything = power consumption 0 mA!
More information about fading here: Fading LED with transistor