ELECTRICAL
Joshua: Are you married, Mr. Kimble?
Detective John Kimble: No, I'm not.
[Joshua sticks his head into the hallway]
Joshua: [shouts] He's not married, Mom!

 

All of our electronic circuits were originally constructed on breadboards. Once the circuits were working, we soldered them on perfboards to give us a more robust system.

 

Battery Module

We created a power board which stacked two batteries in series. This gave us access to a 14.4V line and a 7.2V line. We separated our high power electronics from all of our logic circuits to decrease the potential for noise. We also implemented an emergency-stop which cut power to the actuators but left the logic circuits running. This allowed us to stop all of our motors if something went wrong but keep the logic circuits running.

E128 Module

This diagram shows all of our connections to the E128 microcontroller

 

Flash Sensor, Tape Sensor, and Color Sensor Module

This board contains 4 primary elements. The first is the voltage regulating circuit. We used a low dropout regulator to power this board from a single battery. This means that the logic circuit could be powered even if the battery voltage dropped as low as 5.5V. The second element is the flash sensor. We used a comparator connected to an NPN phototransistor to detect a camera flash. The third element is the tape sensor. We used an IR emitter coupled with an IR phototransistor to detect when we were on a particular color of tape. The output of the circuit fed into an A/D port and we calibrated the reading to determine tape color. The final element is the ball color sensor. It uses an IR emitter and detector to determine whether we obtained a black ball, a yellow ball, or no ball.

Launcher

We used a high power H-Bridge to control our launcher motor with PWM in drive-brake mode. We voltage regulated the launcher so that its speed would be independent of battery voltage. The voltage regulator sees a large amount of current for brief periods of time but once the wheel is spinning, the current draw is low. Thus, the average power dissipation is low and we were able to use a cheaper voltage regulator (L7805) instead of a very high current regulator.

 

Servo and Solenoid

We used PWM to control a servo for ball sorting and a solenoid for dumping black balls.

 

Wheels

We used two high-power H-bridges to control geared Maxon motors in drive-brake mode with PWM.

IR Module

The IR module uses an NPN phototransistor coupled with an amplifier, a filter, and a Schmitt trigger to generate a digital output. We did the following calculations for the circuit:

High Pass filter cutoff:
fc = 1 / (2 π RC) = 1 / (2 π 1.5kΩ * .22uF) = 482 Hz

Beacon Sensor Schmitt Trigger Cutoffs:
VLL = (2.5 V) * R5  / (R4 + R5) = (2.5 V) * 470kΩ / (10kΩ  + 470kΩ) = 2.44 V
VUL =   (2.5 V) * R4 / (R4 + R5 + RPU) + 2.5 V =
(2.5 V)*10kΩ /( 10kΩ  + 470kΩ + 470Ω) + 2.5V = 2.55 V

 

Non-Inverting Amplifier gain:

Ball-requesting side
G = 1 + R2 / R1 = 1 + 27kΩ / 2kΩ = 14.5
Shooting side
G = 1 + R2 / R1 = 1 + 27kΩ / 1.5kΩ = 19