IR Sensors

Two TypesDiode-Phototransistor Pair

Sharp Sensors

Sharp Sensor

Pros● Easy to useCons● Expensive● Large● Noisy readings

Diode-Phototransistor PairPros● Cheap● Small● More accurateCons● Complex to manage

Example Parts• Diode (Emitter): SFH-4545• Phototransistor (Receiver):

TEFT4300• 10SC010075 SC10 3/4 Nylon

Screw Insulators• I will try to get these in the lab

• Black Thermal Tubing• Prevents IR leakage• Use hot-air gun to shrink

Example Setup: Emitter

MCU

GND

5V

0.1 uF 4.7 uF

How to insulate:1. Cut small piece of

thermal tubing2. Put tubing over

emitter so only tip is exposed

3. Use hot-air gun to shrink tubing

Example Setup: Receiver3.3V

MCU

GND

How to insulate:1. Cut a small piece of the

Nylon Screw Insulator2. Use a SMALL amount of

glue to glue it over the TEFT4300

3. Cover with thermal tubing, same way as previous slide

Example Sensor Layout

Position Correction• Wall-in-front correction

• http://micromouseusa.com/?p=398• Corrects angle and translational position• Use twice at dead end to correct X and Y position

• Post detection• http://micromouseusa.com/?p=828• Corrects translational position while on the move• Must calibrate for each speed

Software Tips• Only turn one on at a time• Turn them on only long enough to get a good

reading• Charge period: ~100 us • Discharge period: ~140 us

• Do post-detection and wall-in-front correction• Subtract ambient noise from sensor reading

Maze AdjustmentsSince the Diode/phototransistor pair reads the intensity of the light, the material of the maze walls will significantly change the readings you get.

For example, UCSD uses wooden walls, while UCLA uses plastic walls. The plastic walls will reflect a lot more light. If your mouse is very stable, you might be able to just multiply all your sensor values by a constant to account for the difference. However, in reality the relationship is not always linear, so it may be necessary to re-calibrate all your sensor values.

It is probably a good idea to multiply all your sensor values by 100 or 1000 from the beginning, then you can adjust it up or down as needed when you run your mouse on a new maze. This makes it so you don't need to use floating point to make small adjustments.