SMS – Letter Box

SMS – Letter Box

I am definitely one of those people who are always receiving packages in the mail box. I can’t wait to get home and see which one of my online orders have arrived.

Having wanted to play around with an SMS/GSM phone shield for Arduino for ages, I have been waiting for prices to hit the sub $30 mark.


$30 SMS shield – Quad band modem and antenna supplied

$5 sim card – Includes 365 day access and $5 worth of credit ea SMS @ 12c.

$5 Movement Sensor

$15 Arduino Uno

boardLoad up the shield with your activated SIM card. Mine was bought at an ALDI store for $5, uses the Telstra network and includes 365 day access and $5 worth of credit.

Give the movement sensor 5-20VDC and feed its output into one of the Arduinos inputs.

I did some experimenting with the shield and you may notice it has a modern 4 pin headphone/mic socket that you can use with the usual earbud/mic types supplied with most mobile phones. Yes you can tell the SIM900 modem through its serial port to dial numbers, and i have used it for calls and its brilliant.  Arduino based mobile phone anyone?

installed on box

Place the sensor in the mailbox, and when its opened, you’ll get a text on your phone. I have the incoming text ringtone for that number to a voice file that announces “You’ve got mail!”




I am powering the shield with a plug-pack so I can place it closer to the mailbox.

I have also sent SMS’s to the device to turn ON or OFF relays etc and ask for information such as analog voltages incoming on the pins. I also can SMS the device to turn it off in case it breaks and starts sending lots of SMS’s.  It is also coded to allow triggering only once every ten minutes.

So far it is working remarkably well.

letterbox sensorThere you go, that’s all there is to it.





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