Added concept image and code

prototype/logCurrent/logCurrent.ino

@@ -0,0 +1,89 @@
+#include <SPI.h>
+#include <SD.h>
+
+const int chipSelect = 4;
+
+float sensorValue[4];        // value read from the pot
+// A0: ACS7812 Sensor, A1-A4: USB voltage inputs, A5: Raspberry Pi voltage input
+float sensorPin[4] = {A1, A2, A3, A4};
+int num = 100;
+
+void setup() {
+  Serial.begin(115200);
+  while (!Serial) {
+    ; // wait for serial port to connect. Needed for native USB port only
+  }
+
+  Serial.print("Initializing SD card...");
+
+  // see if the card is present and can be initialized:
+  if (!SD.begin(chipSelect)) {
+    Serial.println("Card failed, or not present");
+    // don't do anything more:
+    return;
+  }
+  Serial.println("card initialized.");
+
+  //we are using Adafruit Adalogger M0 wirh a SAM D21 board.
+  //It has a ADC resolution of 12 bits. Use the highest available resolution
+  analogReadResolution(12);
+}
+
+void loop() {
+  // make a string for assembling the data to log:
+  String dataString = "";
+
+  getData(dataString);
+
+  // open the file. note that only one file can be open at a time,
+  // so you have to close this one before opening another.
+  File dataFile = SD.open("datalog.txt", FILE_WRITE);
+
+  // if the file is available, write to it:
+  if (dataFile) {
+    dataFile.println(dataString);
+    dataFile.close();
+    // print to the serial port too:
+    Serial.println(dataString);
+  }
+  // if the file isn't open, pop up an error:
+  else {
+    Serial.println("error opening datalog.txt");
+  }
+}
+
+// changes dataString to have data in the following format:
+// num1, num2, num3, num4, num5
+// num1: time elapsed in milli seconds 
+// num2-num5: current through corresponding USB port in milliAmps
+
+void getData(String &dataString) {
+  dataString = String(millis());
+  dataString += ", ";
+
+  // zero all readings
+  for (int i = 0; i < 4; i++) {
+    sensorValue[i] = 0;
+  }
+
+  // read and average analog inputs
+  for (int j = 0; j < num; j++) {
+    for (int i = 0; i<4; i++) {
+      sensorValue[i] += analogRead(sensorPin[i]) * 3300 / 4096;
+      //wait for ADC to stabilise
+      delay(2);
+    }
+  }
+  for (int i = 0; i < 4; i++) {
+    sensorValue[i] /= num;
+  }
+
+  // add data to string
+  for (int i = 0; i < 3; i++) {
+      dataString += String(sensorValue[i]);
+      dataString += ", ";
+  }
+  dataString += String(sensorValue[3]);
+
+  //  Serial.println(dataString);
+}