The BenchBot is equipped with 8 ultrasonic sensors that cover a range of 360 degrees of the system. These sensors are used in the feedback of the BenchBot, as an obstacle avoidance algorithm.
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The bot currently is equipped with HCSRF04 ultrasonic sensors, that have a range from 2 cm to 300 cm. The sensor has a resolution of 0.3 cm and works on +5V DC. The data-sheet for the ultrasonic sensors can be found here.
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A simple voltage divider circuit can be used to work with the ultrasonic sensors. Hence, the recommended resistor values are R1 = 1k Ω and R2 = 2k Ω . a mathematically the equation can be defined as:
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After several tests, we found that the ideal values of R2 and R1 should be chosen as per the ratio below.
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Here are some resistor values that works well with the BenchBot design.
Resistor pair values | |||
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R2 | 2 K Ω | 470 Ω | 1.5 K Ω |
R1 | 1 K Ω | 370 Ω | 680 Ω |
How to use the sensor with raspberry pi?
Initialize the Raspberry pi and required libraries.
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import RPi.GPIO as GPIO
import time |
Initialize the Trigger and Echo pins (ex. TRIGGER = 16 , ECHO = 18).
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class UltrasonicInterface():
def __init__(self,trig,echo):
self.GPIO_TRIGGER = trig
self.GPIO_ECHO = echo |
Assign Raspberry pi pins to with the assigned number.
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def setup_ultrasonic(self):
GPIO.setup(self.GPIO_TRIGGER, GPIO.OUT)
GPIO.setup(self.GPIO_ECHO, GPIO.IN) |
Get distance from ultrasonic sensors.
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def distance(self):
GPIO.setmode(GPIO.BCM)
# setting GPIO pins
self.setup_ultrasonic()
# set Trigger to HIGH
GPIO.output(self.GPIO_TRIGGER, True)
# set a small delay and change Trigger to LOW/False
time.sleep(0.00001)
GPIO.output(self.GPIO_TRIGGER, False)
# get the start time
start_time = time.time()
stop_time = time.time()
while GPIO.input(self.GPIO_ECHO) == 0:
start_time = time.time()
# get stop time
while GPIO.input(self.GPIO_ECHO) == 1:
stop_time = time.time()
# time difference between start and arrival
time_occured = stop_time - start_time
# sound speed (34300 cm/s)
distance = (time_occured * 34300) / 2
GPIO.cleanup()
return distance |
How to get data from the sensors?
Create an Ultrasonic Interface object and pass in the TRIG and ECHO pins as arguments.
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ultrasonic_object = UltrasonicInterface(16,18)
dist = ultrasonic_object.distance() |
Resources:
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