Added RPi4 backplate

RackCabinets/RaspberryPi4B/R4_backplate.scad

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+include<../sixinch_library.scad>
+
+
+  ///////////////////////////////
+ // Raspberry Pi 3 Model 4    //
+///////////////////////////////
+
+print_rear           = true;
+
+
+if(print_rear){  // Back plate //    
+    square_hole  = [
+        [37 ,4, 15, 16] , 
+        [55 ,4, 15, 16] , 
+        [73 ,3, 17, 15]  
+    ];
+    
+    round_hole   = [[31,3.5,5],[31,1.2,3.5]];
+    screw_top    = [36];//mm
+    screw_bottom = [36];//mm
+    screw_side   = [];
+    depth        = 98;
+    units        = 2;
+    
+    translate([-22.35,-2.3,-99]){
+        back_plate(units,depth,screw_top,screw_bottom,screw_side,square_hole,round_hole);
+    }
+}  
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