Automatic Mailbox Light
Intro: 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
10 Comments
nwonharp 8 years ago
Good project !
But I myself , IMHO , have always liked simplicity in designs . If you added a third AA battery , and connected them in series , you wouldn't need the " boost converter " . And if all you need to do is find your mail in the mailbox , I don't see why the LED's need to fade and get brighter or dimmer . ( look up : Rube Goldberg and Heath Robinson ) All that you need is the tilt switch , batteries , LED's , and the properly sized resistors .
Cheers , take care , and have a good day !! .........73
nusnus 8 years ago
Thanks!
Simplicity can be defined in many ways. You defined it as a small and easy circuit. In this project I defined it as easy maintenance. A light in the mailbox is something that is helping you, but you do not notice it until it does not work. When that happens you might not have spare parts available. For that reason only one battery is suifficient to get it runing again. And that battery does not have to fresh out of the box. It can be slightly used and it will still light the mailbox for many mail checks.
The boost converter is a super important component. It allows the battery voltage to be anything between 0,2 - 5V. This also means that the bateries will get sucked totally dry before needing to change them.
In your circuit the only color led you can use is red or green. Blue, white, UV... has over 3V forward voltage so they would be very dim or totally off. If you would choose red leds, the forward voltage is 2,2V. This means that when it would be time to change batteries, you would have a ton of energy still left in the batteries = bad design of the system.
About the fading, I agree with you. It is over engineering. It would have been such an easy circuit so I had to put something more in it ;).
mkaislasuo 8 years ago
nusnus 8 years ago
haha kiinni jäin ;D
nusnus 8 years ago
haha kiinni jäin ;D
nwonharp 8 years ago
If you read my comment again , you will see that I suggested a THIRD AA battery and connect them in series , which would give you 4.5 volts , which should light any LED . If you worry about wasting batteries , you could make the project with a small solar panel and rechargeable batteries ( lithium would be a good choice ) or even a large capacitor to store the energy ( more environmentally friendly than the batteries as far as disposal problems when it wears out )
More ideas:
Carry a flashlight ,
Change the burned out bulb in your porch light !!
Cheers , take care , and have a good day !!....73...
nwonharp 8 years ago
Oh yeah ,
How about an audible signal to let you know when the mail is delivered .
Set a mousetrap and put it in your mailbox , and you will hear your mail carrier yell , letting you know that the mail is there !!
Cheers !!
nwonharp 8 years ago
If you read my comment again , you will see that I suggested a THIRD AA battery and connect them in series , which would give you 4.5 volts , which should light any LED . If you worry about wasting batteries , you could make the project with a small solar panel and rechargeable batteries ( lithium would be a good choice ) or even a large capacitor to store the energy ( more environmentally friendly than the batteries as far as disposal problems when it wears out )
More ideas:
Carry a flashlight ,
Change the burned out bulb in your porch light !!
Cheers , take care , and have a good day !!....73...
mec20mb9 8 years ago
I had a similar idea a while ago about adding a light sensor to the inside of the box, that might send an SMS when the mail was delivered. I realized that a mess of wires running into an improvised box sitting inside my mailbox would almost definitely get the bomb squad called.
nusnus 8 years ago
if you make it in a nice box there would not be a problem. I was thinking about adding a IR proximity sensor that would light a led when the distance to the box bottom changes (there is mail in the box)