Wireless Mailbox Notifier

WIRELESS MAILBOX NOTIFIER

This electronic mailbox notifier gives by means of a transceiver, over a distance of a few hundreds of meters, a message that the mail has delivered.
As soon as the lid of the mailbox opens, the transmitter will send for a half second a signal to the receiver in the house. The receiver will produce then an intermitting signal (beep sound or led flash) until reset.
Building the electronic mailbox notifier is not difficult, but it needs some knowledge of electronics.
In our case the signal has to send to the house over a distance of 150m through the forest.

Switch in mailbox

The switch consist of a reed contact which will be activated by a magnet when the lid or the door in the mail box will be opened.
A reed contact is weather proof and it is operated by a magnet. Moreover it has a very long life time and the contact is reliable.
The construction of the reed switch is shown in the added drawings.

The dipolantenna (self-made)

Material:

• 36cm electricity tube 5/8".
• 2 x insulated copper electricity wire
  2,5mm2, length each 17,3cm.

The dipolantenna can easy be made from two insulated electricity wires, each 17.5 cm. To prevent oxidation it is recommended to keep the insulation on the wire. The wave length lambda (in m) can be easily calculated by dividing 300 by the used frequency (in MHz). The result is shown in m. In this case the frequency is 433 MHz, so the wave length is 300:433= 0.69m. A dipol antenna is usally based on 1/4 lambda, so both dipol parts have each a length of 0.69 : 4 = 0,173 (17,3 cm). By placing the wires into a standard 5/8" electricity tube a solid unit will be obtained.

Remark: The distance between antenna and mailbox has to be minimal 8,5cm!