Motorized video projection screen control with digital interface
CROSS REFERENCES 
     None. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to a device for controlling the extension and retraction of a motorized video projection screen. Repeatable positions are allowed which are adjustable along the full length of screen travel between its two mechanical limit switches. 
     2. Description of the Prior Art 
     Motorized projection screens currently in manufacture employ mechanical limit switches to achieve repeatable extended and retracted positions. These limit switches provide only one extended position and full retraction and are adjustable only at the screen itself which may be mounted in an inaccessable place. This device allows control of the screen by: two remotely adjustable repeatable timers, actuated by pushbuttons, one for extension and one for retraction; a toggle switch for full manual control to any position; and a digital logic interface for positioning the screen by means of commercially available computer output boards through software control to any position. 
     SUMMARY OF THE INVENTION 
     This invention will allow more flexible utilization of the motorized projection screen with the many types of video projection devices of our day. This is particularly true with video cassette recorders and computer driven systems where it may be desirable to view both the full screen length and also only a precise section of the screen. The latter case would allow the bottom lines of the projected image to be hidden from public view by falling below the bottom of the screen. These lower lines could then be used for sending commands to the computer, or device projecting the image on the screen, to control that image. 
     Projection screens are not the only product which this device can control. The device has application wherever a product needs an accurate and repeatable source of 120 Volt AC power to accomplish its task; whether by adjustable timers, manual control or through the digital logic interface via computers and similar devices. The size of the 120 Volt AC load would be limited by the ratings of THY1-THY2 (FIG. 1). The duration the power is applied would be determined by R1 and C1 or R2 and C2 (FIG. 1), the actuation of the manual switch SW3 (FIG. 1), or the input to the digital logic interface at connector J2 (FIG. 1). 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The schematic shown in FIG. 1 is the symbolic electronic description of this device. Included in the circuit are an interlock device U4, to lockout unwanted combinations of the other inputs, an adjustable dual timer U3, to provide a remote to the screen adjustable travel period, and a three input NOR gate U5, to allow output triac drivers U1 and U2 to be triggered from: the adjustable timers through SW1 and SW2, the manual switch SW3, or the digital logic interface at J2 via computer boards, etc.. All three methods drive U6 and U7, which, through LED1 and LED2, provide lighted indication of the direction the screen is traveling. An associated power supply and component resistors and capacitors are included to provide proper timing and logic levels for operation of the device. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The circuit in FIG. 1 is composed of two sections. One section, identified below as the UP section, processes inputs from SW1, SW3A, and J2 pins 36 and 21 (J2-36 and J2-21). A level change at any one of these inputs will cause the voltage at J1 pin 1 (J1-1) to rise from zero to 120 Volts AC which can be used to drive the motorized screen UP into its case. The other section, identified below as the DOWN section, processes inputs from SW2, SW3B, and J2 pins 37 and 21 (J2-37 and J2-21). A level change at any one of these inputs will cause the voltage at J1 pin 2 (J1-2) to rise from zero to 120 Volts AC which can be used to drive the motorized screen DOWN out of its case for viewing. 
     When 120 VAC power is applied to the circuit in FIG. 1, 5 volts DC is developed by PS-1 and is applied to each place as shown by the +5. The +5 volt and common connections to power the individual logic devices are assumed, and not shown for clarity. 
     THE UP SECTION 
     SW1 is the &#34;up&#34; pushbutton switch, and it controls the voltage level at connector J1 pins 1 and 3 (J1-1 and J1-3) in the following manner. When SW1 is actuated, the voltage at pin 1 of U4, a QUADRUPLE TWO INPUT AND GATE, changes from low (near zero volts) to high (near +5 volts) due to R7. As long as pin 2 of U4 is also high, which it will be if no other input is calling for an action from the UP section of U5, a TRIPLE THREE INPUT NOR GATE, a high level is also generated at pins 3 and 4 of U4. As long as pin 5 of U4 is also high, which it will be as long as there has been no level change at pins 2, 1 or 13 of U5 requesting an action from the DOWN circuit, a high level is also generated at pin 6 of U4 and pin 2 of U3. U3 is a DUAL NON-RETRIGGERABLE MONOSTABLE ONE SHOT device, configured with its &#34;A1&#34; input (pin 1) held low and its &#34;CLEAR&#34; input (pin 3) held high. In the quiescent state U3&#39;s &#34;Q1&#34; output is low. A rising voltage level on its &#34;B1&#34; input (pin 2) will cause its &#34;Q1&#34; output (pin 13) to change state for the time period set by the values of R1 and C1. A maximum period of 70 seconds is allowed by this device. When pin 13 of U3 goes high, pin 4 of U5 also goes high causing pin 6 of U5 to go low, locking out any action of SW2 by holding pin 9 of U4 low. When pin 6 of U5 goes low, pin 1 of U1, a DC CONTROLLED SOLID STATE AC RELAY, also goes low, triggering TRIAC THY1 &#34;on&#34; through R9; and the voltage level at J1-1 goes from zero to 120 Volts AC for the time period set by R1 and C1. When pin 6 of U5 goes low, pin 9 of U6, a HEX INVERTER BUFFER, also goes low causing its output, pin 8 to go high. When pin 8 of U6 goes high, pin 6 of U7, a DUAL PERIPHERAL DRIVER, also goes high causing pin 5 of U7 to go low, turning on LED1, the UP lamp in SW1 for the same period of time set by R1 and C1. 
     SW3A is the manual &#34;up&#34; toggle switch, and it controls the output at J1-1 in the following manner. When SW3A is actuated, the level at pin 5 of U5 goes from low to high due to R6, causing pin 6 of U5 to go low, locking out any action of SW2 by holding pin 9 of U4 low, and SW1, by holding pin 2 of U4 low. When pin 6 of U5 goes low, pin 1 of U1 also goes low triggering THY1 &#34;on&#34; through R9; and the voltage level at J1-1 goes from zero to 120 Volts AC for the time SW3A is actuated. When pin 6 of U5 goes low, pin 9 of U6 also goes low causing its output, pin 8 to go high. When pin 8 of U6 goes high, pin 6 of U7 also goes high, causing pin 5 of U7 to go low, turning to LED1, the UP lamp in SW1 for the same period of time SW3A is actuated. 
     Connector J2 pins 36 and 21 (J2-36 and J2-21) provide an external digital interface to the &#34;up&#34; circuit for open-collector output type logic devices, and they control the output at J1-1 in the following manner. When J2-36 is pulled low with respect to J2-21, pin 1 of U6 also goes low causing its output, pin 2, to go high. When pin 2 of U6 goes high, pin 3 of U5 also goes high causing pin 6 of U5 to go low, locking out any action of SW2 by holding pin 9 of U4 low, and SW1, by holding pin 2 of U4 low. When pin 6 of U5 goes low, pin 1 of U1 also goes low triggering THY1 &#34;on&#34; through R9; and the voltage level at J1-1 goes from zero to 120 Volts AC for the time J2-36 is held low. When pin 6 of U5 goes low, pin 9 of U6 also goes low causing its output, pin 8 to go high. When pin 8 of U6 goes high, pin 6 of J7 also goes high causing pin 5 of U7 to go low, turning on LED1, the UP lamp in Sw1, for the same period of time J2-36 is low. 
     THE DOWN SECTION 
     SW2 is the &#34;down&#34; pushbutton switch, and it controls the voltage level at connector J1 pins 2 and 3 (J1-2 and J1-31) in the following manner. When SW2 is actuated, the voltage at pin 12 of U4, a QUADRUPLE TWO INPUT AND GATE, changes from low (near zero volts) to high (near +5 volts) due to R8. As long as pin 13 of U4 is also high, which it will be if no other input is calling for an action from the DOWN section of U5, a TRIPLE THREE INPUT NOR GATE, a high level is also generated at pins 11 and 10 of U4. As long as pin 9 of U4 is also high, which it will be as long as there has been no level change at pins 3, 4 or 5 of U5 requesting an action from the UP circuit, a high level is also generated at pin 8 of U4 and pin 10 of U3. U3 is a DUAL NON-RETRIGGERABLE MONOSTABLE ONE SHOT device, configured with its &#34;A2&#34; input (pin 9) held low and its &#34;CLEAR&#34; input (pin 11) held high. In the quiescent state U&#39;s &#34;Q2&#34; output is low. A rising voltage level on its &#34;B2&#34; input (pin 10) will cause its &#34;Q2&#34; output (pin 5) to change state for the time period set by the values of R2 and C2. A maximum period of 70 seconds is allowed by this device. When pin 5 of U3 goes high, pin 1 of U5 also goes high causing pin 12 of U5 to go low, locking out any action of SW1 by holding pin 5 of U4 low. When pin 12 of U5 goes low, pin 1 of U2, a DC CONTROLLED SOLID STATE AC RELAY, also goes low, trigering TRIAC THY2 &#34;on&#34; through R10; and the voltage level at J1-2 goes from zero to ;b 120 Volts AC for the time period set by R2 and C2. When pin 12 of U5 goes low, pin 5 of U6, a HEX INVERTER BUFFER, also goes low causing its output, pin 6 to go high. When pin 6 of U6 goes high, pin 1 of U7, a DUAL PERIPHERAL DRIVER, also goes high causing pin 3 of U7 to go low, turning on LED2, the DOWN lamp in SW2 for the same period of time set by R2 and C2. 
     SW3B is the manual &#34;down&#34; toggle switch, and it controls the output at J1-2 in the following manner. When SW3B is actuated, the level at pin 2 of U5 goes from low to high due to R3, causing pin 12 of U5 to go low, locking out any action of SW1 by holding pin 5 of U4 low, and SW2, by holding pin 13 of U4 low. When pin 12 of U5 goes low, pin 1 of U2 also goes low triggering THY2 &#34;on&#34; through R10; and the voltage level at J1-2 goes from zero to 120 Volts AC for the time SW3B is actuated. When pin 12 of U5 goes low, pin 5 of U6 also goes low causing its output, pin 6 to go high. When pin 6 of U6 goes high, pin 1 of U7 also goes high causing pin 3 of U7 to go low, turning on LED2, the DOWN lamp in SW2 for the same period of time SW3B is actuated. 
     Connector J2 pins 37 and 21 (J2-37 and J2-21) provide an external digital interface to the &#34;down&#34; circuit for open-collector output type logic devices, and they control the output at J1-2 in the following manner. When J2-37 is pulled low with respect to J2-21, pin 3 of U6 also goes low causing its output, pin 4, to go high. When pin 4 of U6 goes high, pin 13 of U5 also goes high causing pin 12 of U5 to go low, locking out any action of SW1 by holding pin 5 of U4 low, and SW2, by holding pin 13 of U4 low. When pin 12 of U5 goes low, pin 1 of U2 also goes low triggering THY2 &#34;on&#34; through R10; and the voltage level at J1-2 goes from zero to 120 Volts AC for the time J2-37 is held low. When pin 12 of U5 goes low, pin 5 of U6 also goes low causing its output, pin 6, to go high. When pin 6 of U6 goes high, pin 1 of U7 also goes high causing pin 3 of U7 to go low, turning on LED2, the DOWN lamp in SW2, for the same period of time J2-37 is low. 
     The best method of accomplishing this circuit is with the list of parts below, constructed on a custom designed printed circuit board and housed in a metal enclosure to insure best noise immunity; with swiches, cables and connectors conveniently located on the surfaces of the enclosure. 
     
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ITEM     DESCRIPTION          TYPE                                        
______________________________________                                    
R1,R2    100k ohm 15 turn trim pot                                        
                              3006P                                       
R3 → R8                                                            
         10k ohm 1/4 watt resistor 10%                                    
                              carbon                                      
R9,R10   150 ohm 1/2 watt resistor 10%                                    
                              carbon                                      
C1,C2    470 uf 15 WVDC pc mount                                          
                              electrolytic                                
U1,U2    Teledyne solid state relay                                       
                              C76AO-1                                     
U3       dual non-retriggerable ONE SHOT                                  
                              74LS221                                     
U4       quad 2-input AND gate                                            
                              74LS08                                      
U5       triple 3-input NOR gate                                          
                              74LS27                                      
U6       hex inverter buffer  74LS04                                      
U7       dual peripheral driver                                           
                              75454                                       
THY1,THY2                                                                 
         400 volt 6 amp TRIAC T2500D                                      
SW1,SW2  EAO form z mom. pushbutton                                       
                              31-121                                      
         EAO lens for above   31-904-7                                    
LED1,LED2                                                                 
         EAO light emitting diode                                         
                              31-967.0-4                                  
SW3      Alcoswitch toggle (on)-on-(on)                                   
                              MTA-206SA                                   
PS-1     Acopian P.S. 5 volt 250 ma.                                      
                              5E25                                        
J1       Philmore 4 pin jack  P606CB                                      
P1       Philmore 4 pin plug  T609CB                                      
J2       Canon 37 pin connector                                           
                              DC-37S                                      
F1       fuse sized to match load                                         
                              3AG TYPE                                    
MISC.    wire, cable, lugs, chassis, etc.                                 
         to mount above components.                                       
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     The values listed above for R1,R2 and C1,C2 will yield a time period which is adjustable from a few milliseconds to over 30 seconds depending upon the tolerances of the components.