Seat cushion switch with delay circuit

A general purpose time delay weight activated switch is disclosed. A foam seat cushion contains wire mesh electrical switch closing contacts. Sitting or rising from the cushion opens and closes the switch. A solid state adjustable timer is also imbedded in the cushion, or adjacent to the cushion. Its purpose is to delay the opening of the switch several seconds. An ideal application for the device is to automaticlly lock an emergency brake in a delivery van. The driver leaving the parked vehicle automatically locks the parking brake or vehicle brakes when leaving the vehicle when the present invention is combined with a parking brake or vehicle brake locking means. The invention's delay circuit allows the driver to bounce up and down on a bumpy road without setting off the switch. Other uses for this special purpose seat cushion include railroad, farm equipment, industrial and power boat safety systems.

SUMMARY OF THE INVENTION 
This invention combines a weight activated seat cushion switch with an 
electronic delay circuit. The device is a self-contained plastic covered 
seat cushion with up to three wires protruding from one edge. It fits on 
any seat suited for humans. The wires can be connected to any safety or 
convenience device which requires activation by sitting on or rising from 
the seat. 
A thin plastic sheet encloses a foam rubber and wire mesh sandwich type 
switch. Two layers of thin foam rubber line the outside of the cushion. 
Underneath lie two sections of electrically conductive wire mesh separated 
by a relatively thick insulating layer of foam rubber. Each layer of wire 
mesh holds several contact washers. These washers pass through matching 
holes in the central insulating foam rubber pad. Matching contact can make 
electrical contact in between the holes when the insulating layer is 
compressed by weight. Normally the washers don't touch, leaving an open 
circuit between the positive and megative lead wires. Sitting on the 
cushion compresses the central insulating foam pad thus allowing one or 
more of the washers to make contact with the opposing washer. 
One lead wire passes through a solid state adjustable delay timer circuit 
board before exiting the cushion. This circuit board uses transistors, 
resistors and relays to delay the opening of the circuit between the 
positive and negative lead wires after the circuit is closed by a person 
sitting on the cushion. A charged capacitor discharging at an adjustable 
rate activates an electronic gate which charges a coil thus opening a 
relay on the lead wire circuit. 
The primary object of this invention is to provide a novel composite switch 
activating seat cushion ideally suited for vehicle safety applications. 
A secondary object is to provide an inexpensive yet rugged design to allow 
for weight to bounce up and down on the device for prolonged periods of 
time without disturbing the functionality of the cushion. 
Other object of this invention will appear from the following description 
and appended claims, reference being had to the accompanying drawings 
forming a part of this specification wherein like reference characters 
designate corresponding parts in the several views.

DETAILED DESCRIPTION 
Referring to FIG. 1, a resilient compressible apertured separator 1 
separates two wire mesh contact sheets 2 and 3 in which conductive 
contacts 4 are mounted on several opposing locations on sheets 2 and 3. 
Holes 5 allow opposing contacts 4 which are preferably washers, to touch 
when separator 1 is compressed. In normal operation this would occur when 
a person sits on the device. Contacts 4 are electrically connected to 
contact sheets 2 and 3. Delay circuit 7 normally fits into slot 10. Lead 
wires 8 and 9 and G are normally connected to whatever activating device 
this invention triggers (not shown). Resilient layers 17 and 18 protect 
contact sheets 2 and 3. Plastic cover 6 provides a protective outer cover 
for the device of the invention. 
During operation twelve volts of DC electric power is applied across lead 
wires 8 and 14 by the activating device this invention triggers (not 
shown). Lead wire G attaches to ground. A typical application using the 
present invention would be a vehicle emergency brake system configured to 
apply the emergency brakes when the driver lifted his weight off the 
invention for more than a few seconds. Typically this total system adds a 
measure of safety to a delivery truck operation requiring numerous park 
and stop maneuvers while the vehicle is running. 
While contact is sensed between contact sheets 2 and 3 by the delay circuit 
7, a direct electic path between leads 8 and 9 is provided by delay 
circuit 7. When contact stops between contact sheets 2 and 3, delay 
circuit 7 electronically delays opening the electric path between lead 8 
and 9 for an adjustable period of time, usually 3-7 seconds. 
Contact points 15 and 16 and wires 13 and 14 provide an electric path from 
sheets 2 and 3 through the delay circuit 7 via input terminal 11. 
FIG. 2 shows delay circuit 7 in position in slot 10. Lead wires 8, 9 and G 
normally protrude through plastic cover 6. Lead wire 14 electrically joins 
wire 8 before exiting cover 6. 
FIG. 3 shows the invention without the plastic cover 6. Wire 14 is shown 
while wire 13 is hidden beneath delay circuit 7 (see FIG. 2). Contacts 4 
are behind delay circuit 7 and do not touch delay circuit 7. Layers 17 and 
18 are double sided adhesive material. 
Referring next to FIG. 5, the circuit of the delay circuit 7 is shown. 
All+symbols mean a twelve volt DC power source is present. Normally when 
power is on the seat switch 50 is closed and capacitor 52 is charged 
through resistor 51. At the same time, reference point 53 serves as a 
comparator 55 input leg carrying an input signal which comparator 55 
compares against reference point 54, the other input leg into comparator 
55. Resistor 56 in series with zener 57 creates a reference voltage at 
point 54 which is lower than 53. 
Positive output from comparator 55 is at point 58 which drops across 
resistors 59 and 60 thus biasing (activating) transistor 61 to the ON 
position. When transistor 61 is ON a current is allowed to flow from power 
source 62 through coil 64 to ground 63. When coil 64 receives current, it 
inductively holds contacts 65 closed. In this condition, reference point 
66 maintains a twelve volt charge to any external device (not show). Diode 
67 is in a conducting state during the above conditions. 
When seat switch 50 opens, power is removed from resistor 51 and capacitor 
52 discharges through variable resistor 68. When reference point 53 
becomes lower than reference point 54, the output of comparator 55 drops 
to zero. Transistor 61 then switches to the OFF position stopping current 
through coil 64 thus causing contact 65 to open in a delayed time after 
seat switch 50 was opened. The discharge time of capacitor 52 as 
controlled by the value of resistor 68 controls the time delay of contact 
65 opening. Coil 64 and contact 65 form an electronic relay 69. 
FIG. 4 shows one physical embodiment of the components described in FIG. 5 
mounted on solid circuit board