Snail-Mail box notifier

I am working on a new version of my snailmail notifier.

Old version:

But the problem with the sensor I hacked into, is that it got very low range. Description says up to 50 meters, but if it reaches 25 meters without anything in between, it is a good day...

So instead I am now looking into what I can do instead. I have looked a bit at using xbee's to do the wireless communication needed between the mailbox and receiver, but the price of them is a bit higher than I would like to spend on that. What could I use instead? I have looked at some NRF24L01 modules too, but they are on 2.4 ghz so I am afraid they will mess up my wifi too, as the 2.4 ghz wireless cameras do...

I have done some experiments with the simple 433 mhz rf modules too, but they also seem to be limited a lot when put into the mailbox (made from 1.5mm steel).

Another problem I also got is how to power it. I have thought about some rechargeable batteries, and then an arduino going to sleep to save power, and then some switches mounted where the letters fall through to wake it up again. But not sure how long that still would last, and what batteries would be good for something like this.

From mailbox to receiver there is 25-30 meters in a straight line.

Anyone got some ideas?

You could use a pair of SIM20 transceivers ( you dont have to do anything to use one as a transmitter and one as a receiver if you want to keep it simple )

They reckon 1500m in free air, I have tested a pair over 150m )( the length of my road ) and they were fine.

Hang a 170mm length of wire from the bottom of the mailbox as an antenna.

I don't know what trigger you will be using to detect a mail delivery, but it could bring the transmitter unit out of sleep, and send a code, and go back to sleep, so the battery should last a year or so?

I use Virtualwire for data transfer, and use the PTT output from the chip to power the transmitter ( it has plenty of warm up time bulit in ) so the only quiescent current is from the Arduino chip itself.

You could skip the Arduino ( scandal ) and use a HT12E chip, and just trigger the transmit enable pin , it will draw nanoamps in standby

Those SIM20 transceivers sounds interesting, but where can you get them? My electronics pushers seems to not have any of them, and google also failing to find me some that would actually show me any prices before buying...

The trigger in the mailbox will just be some simple micro switches with a long arm attached to them. The mail will then slide down of a little metal slide, run over the switches, then fall down to the bottom of the mailbox.

I think I saw you were in Denmark ? you can get a TX2 and RX2 transmitter / receiver pair ( I use them for my scoreboards with 250m range )

Use a HT12E in the mailbox, with the TE pin being shorted to ground by the microswitch, and HT12D to decode , you can latch a LED to show " youve got post " and you can connect a buzzer to the VT ( valid transmission ) pin to sound an alarm.

Sorry Arduino, youre overkiil for this project :slight_smile:

Thank you, will try to contact them to see if I can get some from them...

I will still need an arduino for the receiver because it needs to be connected to my network, and call pushingbox if some other criteria are meet too.

Using the TX2 and RX2 you can use the ardunio at the receiver end, triggered by a VT from the HT12D, or you could use an ardunio both ends with Virtualwire to send the data .