• Hardware
  1. Electrical schemes
  1. Voltage regulator
  2. Microcontroller
  3. Sensors
  4. Actuators
  2. Printed Circuit Boards
  3. Body design
• Software
• Errors

Hardware

1. Electrical schemes

1.1 Voltage regulator

The power source of the robot is a seriescascade of 10 1.2 V rechargable AA batteries which produce 12 V dc. The wheel-motors and kicker-solenoid are powered by this 12 V, but the microcontroller and all other electronical components require 5 V dc. Therefore, we need a voltage regulator which creates 5 V dc.

The capacitor between the battery and the regulator is required to ensure there are no high frequency variations in the supply to the regulator. The capacitor after the regulator is required to supply high frequency variations in the current drawn by the logic chips, which the regulator is not fast enough to react to.

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1.2 Microcontroller

The microcontroller is the heart of the robot because it registers all the sensor information, processes this information and finally controls the actuators accordingly. We chose to work with the PIC 16F877A, because it has a large number of input/output pins. The main advantage of this chip is that it contains  already all the necessary modules for information processing (CPU, program and data memory, input/output interface,...). Therby, we don't need many other electrical components to make it work. Only some basic requirements are necessary which will be explained below.

Clocksignal

Reset

ICSP

To load the program into the microcontroller a special connector is used (PicKit2) which uses In-Circuit Serial Programming

On the figure below, you can see the signal routing between the microcontroller and the sensors, actuators, switches and leds.

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1.3 Sensors

IR-ball detection

An infrared sensor was used to detect the ball. The SFH 303 has a spectral range of sensitivity of: 750nm-1100nm. The maximum sensitivity is around 990nm which is close to λ_ball = 940 nm.

Originally, the sensor was placed in a darlington arrangement to amplify the current coming from the sensor and then the voltage was amplified (see next figure) but afterwards this seemed not needed since the output voltage was large enough and we also had some problems with our opamps. Thus we connected the sensor directly to the microcontroller.

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Side detection

The walls were detected with an infrared detector: Sharp GP2Y0A02. The electronic scheme can be seen in next picture. The potentiometer was used for calibration.

Distance to the ball

To detect the distance between the ball and our robot we used a sharp GP2D12. The electronic scheme was the same as in previous figure. It might not be logical to use such kind of sensor but during our test we were satisfied with the generated output voltage of the sensor because there was not a lot of fluctuation this value. The idea was to put the sensor 4 cm behind the place where we would collect the ball such that it would give a maximum output.

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Grayscale

Three IR-reflective sensors (HOA1405) were used to measure the grayscale and orientation of the robot.

Next figure shows the electronic scheme for this sensor:

The potentiometer was used for calibration, i.e. to remove the offset when the sensor was placed above the black color. This is done by using a difference amplifier with no amplification and afterwards the amplification can be determined manually such that a full range (0 - 5 V) was achieved. Note that the optimum point of response of this sensor is 5 mm, so we also took that into account for our design.

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DC motors

The robot has 3 wheels of which 2 are each driven by a dc motor. The rotation speed and -direction of these motors are controlled by a H-bridge chip. We use 3 signals per H-bridge from our microcontroller to control the H-bridge: a PWM signal on the Enable pin and a high or low signal (5V or 0V) on In1 and In2. The signal on In1 has to be the complement of the signal on In2.

Solenoid

We used a pull-type solenoid for the ball kicker, which operates on a nominal voltage of 12 V dc. It is activated by a short signal from the microcontroller, which gets amplified by 2 transistor in Darlington configuration.

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