Let's Make Robots!

Mailbox sensor

Signals when mail is delivered

Last winter my father asked me if I could make a mailbox sensor for him. That winter was long and cold with lots of snow and he found it frustrating to make his way to the mailbox only to find it empty and had to make a new trip later in the day.

So this is my Christmas project for my father (hopefully he won’t see this post)

I started out ordering a cheap set of transmitter/receiver http://www.robotshop.ca/on-shine-low-cost-tx-rx-1.html it has a range of 90m but the mailbox is only about 10m from his house so it should be ok. The plan was to only send a high signal when the mailbox lid was opened but it turned out that due to noise I had to send a more reliable signal. So this is what I came up with.

To have a steady pulsetrain to look for I added a 555 timer, two resistors and a capacitor to get a steady square pulse. When the lid is opened the micro switch closes the circuit and it starts transmitting the signal. This way it only draws current when the lid is open so the 9V battery will probably work for years. The circuit board is mounted underneath the mailbox but still exposed to whether so I gave it a coat of black plasti dip to make it more resistant.

The micro switch is mounted at the lid.

Inside the receiver box we have the receiver hooked up to a PICAXE 08M, a piezo buzzer for audio alarm and a LED for visual indication if one misses the alarm. The whole circuit draws less than 3mA when waiting for the signal and a bit less pulsing the LED afterwards.

The PICAXE program is short but functional:
symbol LED = 4  
symbol SignalPIN = 1 
symbol Periode = 10
symbol Threshold = 8
symbol Frekvens = w0 

high LED
tune 0, 4,($06,$06,$08)
pause 500
low LED
    count SignalPIN,Periode,Frekvens
    if Frekvens > Threshold then goto Post
    goto main
    high LED
    tune 0, 4,($05,$03,$05,$03,$05,$03,$05,$03,$05,$03)
    low LED
    nap 6
    high LED
    nap 2
    goto Blink


Well, that’s my Christmas present for my dad at least. I admit it’s not a great project and I see that you could order something premade that is probably better for $49,- but what is the fun in that?

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.

Hi, great project! Could you also include schematics for transmitter and receiver. I'm a beginner so the pictures aren't enough for me. My plan is to use an arduino on the receiver side, but I don't know how to build the transmitter.

Thank you.

I don’t have any schematics, I’m sorry.
But the receiver is similar to this http://www.sparkfun.com/products/10533 and for the transmitter you can probably use this http://www.sparkfun.com/products/10535 there are some great information on those pages.
Best of luck.

I don't know if you suffer from mass-media-mailings in Andersen-land, but If you could make a setup that tossed the junkmail in a trash bin, I'd give you $49 for one ;)

That have to wait until version 2.0 next Christmas :-D

I could probably get some sort of Nobel prize for that. 

Simple and efficient, great idea ! :)

You made it! :D Nice one!!

I remember you where planning this :) I know it is going to be one merry christmas *<;-)

Simple and neat job ! :)

How about a small solar panel on the transmitter part, perhaps with a tiny charging circuit ? ;)

As the transmitting circuit is only drawing 30mA for 4-5 seconds a day I don't think I need a solar panel.
If it's a 9V 300mAh battery that is turned on for 5 seconds each day it should last for 19 years :-)

In my last "supplies" order from Spark Fun, I added a pair of the cheapie ($5) TX/RX units to do the exact same thing. Great minds think alike, I guess. Nice clean work as always, Mr. Andersen.


Thank you Chris. Please make a post of your version as well.
Small world :-)