Gravity fed remote mail delivery indicator

A wired mail delivery indicator having a physical construction which forces any size of mail across a groove (20). Slope on the left vertical wall of mailbox (10), slope of panel (14), and force of gravity cause mail to block light beam. The light beam is generated by a photodiode emitter (22) and detected by a photo detector (24). Mailbox and electronic circuitry (26) contains photodiode emitter (22), photo detector (24), current limiting resistor (42), and current amplifier transistors (46 and 48). House end electronic circuitry (28) contains power transformer (32), diode rectifier (34), and current sensor (38, 40, and 36). House/mailbox connecting wire (18) carries power and mail delivery information with two wires.

BACKGROUND 
1. Field of Invention 
This invention relates to indicators, specifically to one which tells if 
mail has been deposited in a mailbox at a remote location. 
2. Description of Prior Art 
Heretofore, mail delivery indicators used mechanical switches and 
mechanisms to indicate the presence of mail in the box. Others, such as 
the device in U.S. Pat. No. 4,868,543 to Binkley (1989) required battery 
maintenance, used valuable radio spectrum, and used complex circuitry. 
Mailbox in U.S. Pat. No. 4,499,372 to Nakano (1985) employed complex 
electronic circuitry as above and used multiple emitter/detector pairs. 
Until now, mail delivery indicators known suffer from a number of 
disadvantages: 
(a) Their design requires the periodic replacement of batteries in the 
mailbox. 
(b) Complex electronic circuitry is required. 
(c) Multiple emitter/detector pairs or complex sensor signal paths are 
used. 
(d) Wired versions require more than a single pair of wires. 
(e) Radio transmissions from the remote mailbox result in reduced privacy. 
(f) Valuable radio spectrum is used for radio transmissions from the remote 
mailbox. 
OBJECTS AND ADVANTAGES 
Accordingly, several objects and advantages of my invention are: 
(a) to eliminate the need for periodic replacement of batteries in the 
mailbox. 
(b) to simplify the electronic circuitry required. 
(c) to reduce the number of emitter/detector pairs and sensor signal paths 
to one. 
(d) to reduce the number of wires needed in wired versions to one pair. 
(e) to increase privacy of the system. 
(f) to reduce the usage of valuable radio spectrum. 
Further objects and advantages of my invention will become apparent from a 
consideration of the drawings and ensuing description of it.

DESCRIPTION--FIGS. 1 to 3 
FIG. 1 shows a perspective view of a version of my mail delivery indicator. 
A mailbox 10 is supported by a support post 16. In the backround is a 
house 30. In house 30 is a house end electronic circuitry 28. This 
circuitry is mounted at eye level within house 30. A house/mailbox 
connecting wire 18 runs between mailbox 10 and house 30. Wire 18 can be 
located above or below ground. Within mailbox 10 is a panel 14 which is 
positioned diagonally within mailbox 10. A mail holding area 12 is the 
area between panel 14 and the top of mailbox 10. The space between panel 
14 and the bottom and right sides of mailbox 10 is an area for mailbox end 
electronic circuitry 26. This is where an electronic circuit associated 
with mailbox 10 is mounted. 
FIG. 2 shows a detailed view of the panel assembly. A groove 20 runs along 
a path from the front to the rear of panel 14. Groove 20 is a furrow which 
is about 4 mm wide and 1.5 mm deep in panel 14. It is located about 76 mm 
from the lower end of panel 14. Panel 14 is about 466 mm from front to 
rear. It is about 200 mm from the low end to the high end. A photodiode 
emitter 22 and a photo detector 24 are located at opposite ends of panel 
14. Emitter 22 and photo detector 24 connect by wires to electronic 
circuitry on the lower side of panel 14. 
FIG. 3A is a detailed schematic of house end electronic circuitry 28. It 
consists of a power transformer 32, a diode D1 34, a diode D2 40, a light 
emitting diode D3 36, and a resistor R1 38. These parts are all mounted on 
a printed circuit board. 
Likewise, FIG. 3B is a detailed schematic of a mailbox end electronic 
circuitry 26. It consists of a resistor R2 42, a photodiode emitter 22, a 
resistor R3 44, and a bypass resistor R4 50. It also contains detector 24, 
a transistor Q1 46, and a transistor Q2 48. These components are also 
mounted on a printed circuit board. Both circuitry 28 and circuitry 26 are 
attached by wire 18. 
OPERATION--FIGS. 1 to 3 
When any size of mail is deposited in the box, the light beam which follows 
the path of groove 20 is blocked. This reduces current in wire 18 to less 
than 10 mA. This occurs because emitter 22 and detector 24 are mounted so 
that the maximum light output and detection sensitivity are in the plane 
of the top surface of panel 14. Detector 24 does not sink current when it 
detects no infrared emission from emitter 22. As long as mail is in the 
box and the infrared beam is blocked somewhat less than 10 mA will flow in 
a series circuit thru D1 34, R1 38, D2 40, R2 42, emitter 22, and R4 50. 
Current will not flow thru D3 36 when the current in wire 18 is less than 
10 mA. This is because the forward bias on D2 40 is about 0.7 V. Current 
will flow thru R1 38 and D2 40 until the total voltage across R1 38 and D2 
40 reaches 1.9 V. A current sensor comprises D3 36, R1 38, and D2 40. 
If no mail is contained in mailbox 10, the light beam path in groove 20 is 
not blocked and current flows thru detector 24. This current thru detector 
24 is amplified by Q1 46 and Q2 48 to greater than 10 mA, turning on D3 
36. An amplifying means comprises R3 44, Q1 46, and Q2 48. D3 36 is 
visible to the occupant of house 30. Whenever D3 36 is lit the occupant of 
house 30 knows that no mail is contained in mailbox 10. 
Transformer 32 converts 120 VAC to 16 VAC. A voltage source comprises 
transformer 32. D1 34 is needed because of the low reverse voltage rating 
of D3 36 and emitter 22. R2 42 is needed to limit current thru emitter 22 
if the specified 100 to 300 gains of Q1 46 and Q2 48 are near the high 
end. R3 44 limits current thru detector 24. Panel 14 and a slight inward 
tilt on the left wall of mailbox 10 work together to force any size of 
mail larger than 80 mm wide aross groove 20. If, for example, mail is 
inserted in a vertical plane near the left wall of mailbox 10, the slight 
tilt on the left wall will force the mail down across groove 20. If, on 
the other hand, mail is inserted in mailbox 10 above and to the right of 
groove 20, gravity will force the mail to slide down across groove 20. 
This system allows for the use of a single emitter 22/detector 24 pair. 
The seam between mailbox 10 and panel 14 must not have a gap, otherwise 
mail can get caught and held vertically in it. 
SUMMARY, RAMIFICATIONS, AND SCOPE 
Thus the reader will see that the gravity fed mail delivery indicator is a 
simple, economical, yet effective device with widespread potential appeal. 
Furthermore the mail delivery indicator has the additional advantages that 
it eliminates the need for periodic replacement of batteries in the 
mailbox; 
it simplifies the electronic circuitry required; 
it reduces the number of emitter/detector pairs and sensor signal paths to 
one; 
it reduces the number of wires needed in wired versions to one pair; 
it increases privacy of the system; and 
it reduces the usage of valuable radio spectrum. 
While my above description contains many specifities, these should not be 
construed as limitations on the scope of the invention, but rather as an 
exemplification of one preferred embodiment therof. Many other variations 
are possible. For example, the overall shape of the mailbox can be 
changed. The area for mailbox end electronic circuitry can be reduced. The 
only constraints are for a design where gravity forces any size of mail 
into the light beam path while using a single emitter/detector pair. 
An alternative version of the mailbox end circuit places the emitter and 
detector circuits in parallel instead of in series. Also, the 
emitter/detector pair used can have infrared or visible light wavelengths. 
Accordingly, the scope of the invention should be determined not by the 
embodiments illustrated, but by the appended claims and their legal 
equivalents.