Line Sensing

Notes, designs, and pictures on the Line Sensor.

Initial Design
Initially, we juggled a few design ideas. These included: We eventually decide upon using 2 QRD1114  Reflective Object Sensors in a line configuration, one in the middle of the robot and one at the very front.
 * IR Emitter-Detector Pair sensor
 * IR beacon and a photodiode
 * 3 sensors in triangle shape
 * 2 sensors in a line

Calculations
We need to limit current flow across both the photo-transistor and LED emitter.

Photo-transitor
We want Ic > 100 uA to stay in saturation zone.

Vce = 0.4 in saturation.

R < V/I -->  R < (5V - 0.4V) / 100uA

We want an R < 46k. We choose a 33kOhm resistor, as 33k +- 5% is still less than 46k.

LED Emitter
We want a current of around 20mA. Then 5V / 20mA = 250 Ohms. We choose a 200 Ohm resistor, since the total current will be less after factoring in the forward voltage drop of the LED.

Testing Data
'T' stands for the sensor with tape on it, and 'NT' stands for the sensor without tape on it. The number following is the value the Arduino read.