diff --git a/common.scad b/common.scad
index e7f6b19..eb0947b 100644
--- a/common.scad
+++ b/common.scad
@@ -211,4 +211,38 @@ module geared_motor () {
   translate([-(46 / 2) + 14.5, 0, -(1 / 2) - 10.5]) cylinder(r = 13 / 2, h = 1, center = true, $fn = 60);
   //mount pads
   translate([-0.5, 0, -(1.5 / 2) - 10.5]) motor_mounts();
+}
+
+module opto_endstop () {
+  difference(){
+    union(){
+        // base PCB
+        color("green") cube([33.0,1.6,10.5]);
+        // add the switch module
+        translate([8.4,1.6,10.5/2-6.4/2]) optoswitch();
+        // connector
+        translate([0.2,-7,0]) color("white") cube([5.8,7,10.5]);
+        // led
+        translate([3.5,1.6,10.5/2-1.5/2]) color("red") cube([2,0.7,1.5]);
+    }
+    translate([8.4,0,10.5/2-6.4/2]) {
+      for ( hole = [2.75,24.5-2.75] ){
+        rotate([90,0,0]) translate([hole,6.4/2,-4]) cylinder(r=1.5, h=4.5,$fn=40);
+      }
+    }
+  }
+}
+
+// switch module
+module optoswitch() {
+    difference(){
+        union (){
+            color("gray") cube([24.5,3.5,6.4]);
+            color("gray")translate([6.63,0,0]) cube([4.45,11.3,6.3]);
+            color("gray")translate([13.63,0,0]) cube([4.45,11.3,6.3]);
+        }
+        for ( hole = [2.75,24.5-2.75] ){
+           rotate([90,0,0]) translate([hole,6.4/2,-4]) cylinder(r=1.5, h=4.5,$fn=40);
+        }    
+    }
 }
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