docs update

docs/Assignments/week_12_machine_building/machine_building.md

@@ -501,3 +501,55 @@ So the main MCU would do all the thinking and readings from the sensors and the
     ```
 
 So now I could send commands to the motors over Serial and see the motors spin in realtime. The command is structured like this. `1,500` Where 1 is the motor number and 500 is the speed of the motor. So like this I could control every motor separately. 
+
+## Getting ultrasonic sensors to work (Again)
+On the last day I tried to connect everything together. I first started out with one ultrasonic sensor but I noticed I wasn't getting any data from it. So I started debugging and only running the code necessary to get the sensor running but that also didn't work
+
+??? Code
+    ```cpp
+    int trigPin = D4;    // Trigger
+    int echoPin = D9;    // Echo
+    long duration, cm, inches;
+    
+    void setup() {
+      //Serial Port begin
+      Serial.begin(9600);
+      //Define inputs and outputs
+      pinMode(trigPin, OUTPUT);
+      pinMode(echoPin, INPUT);
+    }
+    
+    void loop() {
+      // The sensor is triggered by a HIGH pulse of 10 or more microseconds.
+      // Give a short LOW pulse beforehand to ensure a clean HIGH pulse:
+      digitalWrite(trigPin, LOW);
+      delayMicroseconds(5);
+      digitalWrite(trigPin, HIGH);
+      delayMicroseconds(10);
+      digitalWrite(trigPin, LOW);
+    
+      // Read the signal from the sensor: a HIGH pulse whose
+      // duration is the time (in microseconds) from the sending
+      // of the ping to the reception of its echo off of an object.
+      duration = pulseIn(echoPin, HIGH);
+    
+      // Convert the time into a distance
+      cm = (duration/2) / 29.1;     // Divide by 29.1 or multiply by 0.0343
+      inches = (duration/2) / 74;   // Divide by 74 or multiply by 0.0135
+      
+      Serial.print(inches);
+      Serial.print("in, ");
+      Serial.print(cm);
+      Serial.print("cm");
+      Serial.println();
+      
+      delay(250);
+    }
+    ```
+
+I double, triple checked every connection and grabbed new wires in case that was the issue. After a while a directly connected it to the mcu but that also didn't work and then I gave up.
+
+![alt text](image-13.png)
+
+After going to Henk and reading the datasheet he said I needed to use 5 volts instead of 3.3 volts
+When I changed that connection it worked.