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Pins & Constants

This page lists every #define constant used in the motor lab files and what it means. These are defined for you at the top of each .c file — you do not need to write them yourself.

Motor pin constants

Constant Value What it controls
L293_ENABLE 26 Motor speed — this is the PWM pin connected to the L293 enable input
L293_INPUT1 21 Motor direction pin A
L293_INPUT2 22 Motor direction pin B
PWM_MAXVAL 1024 Maximum PWM value — represents 100% motor speed

How the motor pins work together

L293_ENABLE controls how fast the motor spins (via PWM). L293_INPUT1 and L293_INPUT2 together control the direction. The two direction pins must always be set to opposite values — one HIGH and one LOW. See The motor driver for details.

Joystick constant

Constant Value What it means
X_INPUT 100 The ADC channel for the joystick X axis (pinBase 100 via the MCP3008)

Logic level constants

These are defined by wiringPi and available in all the lab files:

Constant Value Meaning
HIGH 1 Digital on (approximately 3.3 V on a GPIO pin)
LOW 0 Digital off (0 V)

Pin mode constants

Constant Meaning
OUTPUT Pin is used for digital output (on/off)
PWM_OUTPUT Pin is used for PWM output (variable power)

See also