Have you ever made
multiple trips to your
mailbox hoping the
mailman had delivered
that important letter
or even better, that
long awaited check?
This handy gadget will
end those many unfulfilled trips and indicate
via a lit LED and/or
sound alert that your
mail has been delivered.
After you pick up your
mail, you simply press a
reset button and your
Detector is ready for the
next day’s mail delivery.
The Detector consists of a transmitter located in or by your
mailbox, and the receiver can be
located anywhere else you desire,
probably in a room where you
spend most of your time. The
Detector I built for myself does not
contain a “sound alarm,” but one
may be easily added if you need it.
The heart of the Detector is the
432.9 MHz transmitter and receiver
modules from Reynolds Electronics.
The receiver module is a very sensitive super-regenerative receiver,
while the transmitter has a 16 dBM
output which may be easily
amplitude- or pulse-modulated.
Each module is only $8.50 and can
be ordered over the Internet.
In my first prototype, I used an
old remote control transmitter and
receiver module from a remote controlled car operating at 27 MHz. That
frequency is quite noisy because it is
in the middle of the CB band.
Although the prototype worked
quite well because of key features in
the circuit, the Reynolds modules are
much better at 432.9 MHz.
Figure 1 shows how simple the
Detector is. The transmitter module
■ FIGURE 2
■ FIGURE 3
2 x 2N4403)