Update README.md, images/calipers_breadboard.png, images/caliper_port.png,...

Update README.md, images/calipers_breadboard.png, images/caliper_port.png, images/caliper_scope.png, serial_Caliper.ino

README.md

 # Serial Caliper
 
-Many of the common cheap digital calipers avaliable on Amazon/Ebay share a relatively easily accessible serial port and protocol at the back of the head, consisting of battery power, ground, and an I2C adjacent serial interface consisting of a CLK and SDA line. 
+Many of the ubiquitous $20 calipers found on amazon and ebay share a relatively accessible serial port and protocol tucked behind the battery compartment. This means that with a level shifter (the calipers run a single coin cell resulting in 1.6V logic level) it's possible to get 10um linear measurement resolution to a microcontroller without having to resort to more expensive linear encoders.
+
+<img src="./images/caliper_port.png" height=400 />
+
+The caveats are that these calipers are only running at only about 2sps, so not useful for real time loop closing, and the protocol is peripheral-less and must be bit-banged which eats up MCU resources.
+
+Here's a [good reference](https://sites.google.com/site/marthalprojects/home/arduino/arduino-reads-digital-caliper) for getting initial results. I made a few changes in code including printing binary packets for debugging, and flipping all of the reads (we are using a level shifter not a transistor). See below for a simple breadboarded circuit to get up and running.
+
+<img src="./images/caliper_breadboard.png" height=600 />
+
+Raw scope readings (reading a 0.01mm) can be seen below, transmitted over seven 4-bit chunks. The readings are fixed point with the two LSB in decimal being devoted to 100 and 10 um significant figures. The 21st bit is devoted to measurement sign, and one of the remaining bits is used for unit conversion, while some are unused.
+
+<img src="./images/caliper_scope.png.png" height=600 />

serial_Caliper.ino

+int i;
+int sign;
+int value;
+float result;
+int datapin = 15;
+int clockpin = 14;  
+unsigned long tempmicros;
+bool bitval[24];
+
+ 
+void setup() {
+    Serial.begin(9600);
+    pinMode(clockpin, INPUT);
+    pinMode(datapin, INPUT);
+}
+
+void loop () {
+    while (digitalRead(clockpin) == LOW) {} //wait for the end of the HIGH pulse
+    tempmicros = micros();
+    while (digitalRead(clockpin) == HIGH) {} // wait until we go high again (skips first bit)
+    if ((micros()-tempmicros)>500) {
+        decode(); //decode the bit sequence
+    }
+}
+
+void decode() {
+  sign=1;
+  value=0;
+
+  for (i=0; i<23; i++) {
+    while (digitalRead(clockpin) == LOW) { } //wait until clock returns to HIGH- the first bit is not needed
+    while (digitalRead(clockpin) == HIGH) {} //wait until clock returns to LOW
+    if (digitalRead(datapin) == HIGH) { // in original example an NPN transistor was used which flipped the output loic (low = 1, high = 0). If using a proper logic level shifter this would be reveresed 
+        // So if we are reading a bit
+        if (i<20) { // And if we are within the first 20 bits of data
+            bitval[i] = 1;
+            value|= 1<<i; // Shift the bit to its correct order of magnitude (see bit shifting), and add it (using the or operator) with value (which is acting like a sum)
+        }
+        if (i==20) { // The 21st bit is the sign bit, which if 1 means we are reading a negative value
+            sign=-1;
+        }
+     }
+   else {
+      bitval[i] = 0;
+   }
+  }
+  result=(value*sign)/100.00;    
+  Serial.println(result,2); //print result with 2 decimals
+  /*
+  for (i=0; i<23; i++) {
+      Serial.print(bitval[i]);
+  }
+  Serial.println("");
+  */
+  //delay(1000);
+}