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+.TL
+Notes on work done 
+.AU
+Lucas Standen + Nigel Standen
+.AI
+29/5/24
+.NH 1
+How the current of an LED can effect the wavelength of the output
+.NH 2 
+The experiment
+.LP
+In the experiment we measured how the wavelength of an LED is effected by the current passed through
+it. The results lead one to believe that as current increases the wavelength does too.
+
+We made sure to measure using a pulse, rather than a continuous current, this is to ensure that the 
+thermal energy that the LED gives off, does not effect its results; however we believe our pulse
+was still to long and that it did effect the results.
+
+The pulse is generated by an Arduino with a simple script running, allowing me to press a button
+that triggers the power supply and the spectrometer (tool used to measure wavelengths). Before 
+starting the experiment, we took a reading of ambient temperature, as we were looking at 
+current (which effects temperature) against wavelength.
+
+We found the temperature to be 
+.B "20 deg C".
+
+.NH 3
+Triggering circuit
+.LP
+The triggering circuit was kept simple, with most things being done in code, one thing of note 
+however is that the push button used as a trigger is in a push to make configuration.
+
+To wire the circuit follow these steps:
+
+1) Attach a button between pin 2, and ground.
+
+2) Attach pin 7 to the spectroscope's live input, and attach its ground to a ground rail on the
+bread board.
+
+3) Attach pin 8 to the PSU's live input and its ground to a shared ground.
+
+4) Using the Arduino ide, flash the code (can be found on the USB you gave me).
+
+5) Set up the program on the PSU to have a pulse duration as long as you need, and then press the
+button.
+
+.LP
+The code for this can be seen here as well:
+.LP
+.B1
+const int instrument1Pin = 7; // Pin for instrument 1 (0V to 5V) Spectroscope
+
+const int instrument2Pin = 8; // Pin for instrument 2 (5V to 0V) PSU
+
+const int triggerPin = 2; // the pin the button is connected too (active high)
+
+// Configure pulses
+const int pulseDurationInMs = 100;
+const int psuDelayInMs = 30;
+
+void setup() {
+        // Configure pins
+        pinMode(instrument1Pin, OUTPUT);
+        pinMode(instrument2Pin, OUTPUT);
+        pinMode(triggerPin, INPUT_PULLUP);
+
+        // Initialize pins
+        digitalWrite(instrument1Pin, LOW); // LOW corresponds to 0V (min value)
+        digitalWrite(instrument2Pin, HIGH); // HIGH corresponds to 5V (max value)
+
+}
+
+
+void loop() {
+        if (digitalRead(triggerPin) == LOW){
+                // Create pulses
+                digitalWrite(instrument2Pin, LOW);
+                delay(psuDelayInMs);
+                digitalWrite(instrument1Pin, HIGH);
+
+                delay(pulseDurationInMs - psuDelayInMs);
+
+
+                digitalWrite(instrument2Pin, HIGH);
+                delay(psuDelayInMs);
+                digitalWrite(instrument1Pin, LOW);
+                delay(1000);
+        }
+
+}
+.B2
+.LP
+It is relatively simple in function, when the switch on pin 2 goes high, it will send a low to the 
+PSU (the PSU is active low in this case) and a high to the spectrometer (active high). The setup
+function (defined in the first set of {}) is used to initialise the pins, and the loop function
+will be run as fast as the microcontroller can. It constantly checks if the trigger pin goes low 
+(the button has shorted pin 2) and if it does it sends a pulse of pulseDurationInMS down
+each wire. The variable psuDelayInMs is used to set how much sooner the PSU will trigger compared 
+to the spectrometer.
+
+.NH 2 
+The results
+.LP
+We measured results using a green LED, and our pulse's had a width of 450ms
+
+A graph of results can be found below:
+.PSPIC graph.ps
+.LP
+.I "y axis = wavelength (nm), x axis = current (mA)"
+.LP
+I modelled a line of best fit for this graph to be y = 1/9x + 568.4, with X being the current in mA, 
+and Y being the wavelength in nm; however this is just by eye. From this one can assume the 
+temperature coefficient to be 1/9 nm/mA.
+
+The results show that as the LED had more current flowing through it, the colour of the light it
+produced changed to a higher wavelength (towards red).
+
+It is worth noting that when we reduced the pulse duration to 300ms instead of 450ms, at 30mA
+the wavelength fell to 570.61nm, which suggests that even on a pulse as small as 450ms the heating 
+of the LED has effected its wavelength.
+
+Of note we found that there was a tiny delay between when the when the spectrometer went high, and
+the PSU went low, we found it to be around 6us, we believe this to be because the spectrometer is
+set to go high first.
+
+This effect can be seen in this oscilloscope:
+.PSPIC scope.ps
+.I "The yellow traces is the spectrometer, the blue is the PSU"
+
+.NH 2 
+Takeaways
+.LP
+From this experience I think I should takeaway that, first LED's are effected by temperature very
+slightly, and that the equipment resolution/accuracy is important to note, my results may be wrong,
+however the trend shown by that graph is correct, I find this interesting and important.
+
+I've believe this work will help me in further life, it really has been my first glimpse into a real
+working world with electronics, I look forward to working more on it.
+
+.NH 1
+Building LED's
+.LP
+The process consists of taking the die which is made from silicon and a handful of other metals
+that decide the wavelength of the light emitted. The die is placed on a package with apoxy, that
+contains silver, then a wire is bonded to the top (see pictures), to the other part of the package.
+
+Here is some images of the process or wire bonding LED's:
+.PSPIC wirebonds.ps
+.I "A view of the die on the package, and the machine"
+.PSPIC wirebonds2.ps
+.I "A view through the lens"
+.LP
+This was a very interesting process to see, I always imagined an LED as one bit of metal that did
+the job, I had never through how much precision work went into it. The LED's we worked on 
+were 280um x 280um.