It's a little wibbly-wobbly cutie.
- atmega32u4 board
- sparkfun redbot chassis
- drv8835 dual motor driver carrier
- HC-SR04 ultrasonic sensor
- lots of duct tape and zip tie
PWM1 at PB4 and PWM2 at PB7.
To control motors I use DRV8835 driver.
This driver needs voltage supply, for logic and for motors.
I feed both VCC from my board VCC. Currently I don't use any external power source except from USB connected to board.
Motor driver has two channels, that enable it to control two motors.
Motor driver has two possible modes of operation. I use the simpler one.
To control motor you need to specify phase (should it rotate clockwise or anticlockwise?) and speed. Phase is specifide by logic value on digital pin of motor driver and speed is controlled by PWM pin.
Robocar uses HC-SR04 sensor.
I wrote a simple library to interface with it.
This sensor is really easy to use. It has VCC, ground, trigger which waits for inputs and echo pin which outputs signal of length proportional to distance of an obstacle.
Sound wave travels to obstacle and back to sensor. If we divide time it takes by two and speed of sound we get distance.
I used this tutorial which uses similar sensor (but with only one pin for communication with a sensor).
Ultrasonic motor is placed on a servo motor which rotates it. This setup creates a radar which enables robot to scan it's environment and choose the best path to go.
I use blinking diodes to debug how sensors are working using color codes.
- green - no obstacle detected in front of the robot (rare)
- red - distance sensor not working correctly
- blinking - can ride without problems
- constant light - obstacle detected really near the robot, robot needs to reverse immediately
I used small servo of unknow brand. It was lying around.
It has three inputs:
- control signal
I control it using PWM on 50 Hz. Different duty cycles enable me to set servo to different angles.
Here is a design picture created using fritzing.
Design is a bit messy, but it's only a prototype on breadboard. I haven't done any pcb yet.
Software is written in C for atmega32u4.
Programs starts with initializations.
Here are initialized components:
- ultrasonic sensor
- radar (servo rotating ultrasonic sensor)
In main loop everything starts from radar measuring a distance and storing it to appropriate cell in table of measured distance for different angles.
Then robot checks how much space is available for it if running forwards. If sensor works correctly and there is no obstacle nearer than 10 cm, robot chooses the best direction to turn based on amount of available space. The farther from obstacle, the better.
If sensor detects an obstacle in front of it, it reverses, turning in the same time.
The choice of angle is based on
distance_values for angles.
After that it stops and scans an environment with radar to update `distance_values.