added more apparatus details

pulseox/README.md

@@ -262,6 +262,16 @@ void loop() {
   }
 }
 ```
+The fabricated sensor board was designed in KiCad around a commonly available op-amp and photodiode:
+
+![schematic](../img/apparatus_schematic.png)
+
+... and laid out for single-sided PCB milling using a 1/64" mill:
+
+![layout](../img/apparatus_layout.png)
+
+After assembly, the PCBs required a bit of sanding for a snug fit in the finger sleeve. Prior to use, a cut piece of neoprene was adhered to one side to provide padding and a bit of finger size accomodation.
+
 See my [NMM final project page](http://fab.cba.mit.edu/classes/864.20/people/zach/final.html) for a first pass at data analysis.
 
 ### Practical Considerations

pulseox/v1_teensy/v1_teensy.kicad_pcb

@@ -18,7 +18,7 @@
     (34 B.Paste user)
     (35 F.Paste user)
     (36 B.SilkS user)
-    (37 F.SilkS user)
+    (37 F.SilkS user hide)
     (38 B.Mask user)
     (39 F.Mask user)
     (40 Dwgs.User user)