28 October 2013
BUILD IT YOURSELF
BUILD THE WIRELESS
By Ron Newton
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october2013_newton for any
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I started off this article with the intention of designing a "You Have Mail" transmitter and receiver.
However, I discovered my circuit has many other applications, so I decided to design a board which
would widen the scope to a large group of sensors that can be used with the transmitter.
The following projects have locations included on the board for the measurement of: temperature,
vibration, light, sound, motion, normally open switch, normally closed switch, any varying resistor input,
voltage input, mA input, tilt, position, water, humidity, Hall detector (magnetic), proximity (motion), and
trespass detector to name a few. Schematics for these are included at the article link, along with the
parts lists for each circuit.
You Have Mail
Quite often if you have a farm or even if you live in
an urban area without home delivery, the mailbox is a
fair distance from the house. Where I live, the mail is
delivered to a drive-by mailbox only 50 feet from the
house. However, there is a fair amount of theft that
takes place with Social Security checks in our area. This
makes it very important to get the mail as soon as it’s
delivered. Linx offers transmitters and receivers that they
list as good up to 3,000 feet — a little over a half mile —
which I utilize in this project.
The circuit presented here works both in collective
mailboxes and with standard lunch box style receptacles,
and is adaptable. With a collective mail box, the device is
mounted on the door with Velcro™ or double-sided tape.
When the mailman opens the door, it detects light and
activates the unit using a photodetector. It is important
to mount the unit on the door so that it exposes the
antenna and prevents a Faraday effect if placed in the
The unit transmits only one second and then goes to
sleep. This trips the receiver which latches and sounds an
alarm, then changes an LED from green to red. The
alarm is reset by pressing the reset button on the
receiver. You can use the same photodetector or a tilt
switch in the lunchbox style mail bin.