I have an HRLV-EZ4 ultrasonic sensor hooked up to my RPi 3 B+ like so:
Serial output --> pi RX (pin 10)
V+ --> pi 5V
GND --> pi GND
I've already gotten it to work with an analog voltage output and an analog-digital converter, but it was not as accurate as I would have liked it to be.
I'd like to write a script that uses serial to read the incoming data from the sensor, but I am new at this and unsure of where to go from here. The sensor is currently configured to use TTL (9600 baud, 8-bit), but I can change it to RS232 if needed. Here's the datasheet for more information. Any help is appreciated.
EDIT: I've tried using this module and script I found before, but to no avail.
# Filename: maxSonarTTY.py
# Reads serial data from Maxbotix ultrasonic rangefinders
# Gracefully handles most common serial data glitches
# Use as an importable module with "import MaxSonarTTY"
# Returns an integer value representing distance to target in millimeters
from time import time
from serial import Serial
serialDevice = "/dev/ttyAMA0" # default for RaspberryPi
maxwait = 3 # seconds to try for a good reading before quitting
def measure(portName):
ser = Serial(portName, 9600, 8, 'N', 1, timeout=1)
timeStart = time()
valueCount = 0
while time() < timeStart + maxwait:
if ser.inWaiting():
bytesToRead = ser.inWaiting()
valueCount += 1
if valueCount < 2: # 1st reading may be partial number; throw it out
continue
testData = ser.read(bytesToRead)
if not testData.startswith(b'R'):
# data received did not start with R
continue
try:
sensorData = testData.decode('utf-8').lstrip('R')
except UnicodeDecodeError:
# data received could not be decoded properly
continue
try:
mm = int(sensorData)
except ValueError:
# value is not a number
continue
ser.close()
return(mm)
ser.close()
raise RuntimeError("Expected serial data not received")
if __name__ == '__main__':
measurement = measure(serialDevice)
print("distance =",measurement)
The 'raise runtime error' close to the bottom kept giving me trouble, and even if I commented it out, the module wouldn't pick up a reading (IE distance would be 0).
EDIT2: Here's a sample of the output from a script that just reads the data using .read(). It continually updates at 9600 baud.
R
0
4
5
1
R
0
4
5
1
R
0
4
5
1
This is the distance of an object from the sensor in mm that will be used to control a robot. My goal right now is to have that be a single updating entity that can be easily referenced in other modules/scripts. Once the reading falls below a threshold, it will trigger an event/action. The ultimate goal is to have this be differential, so that the robot can respond to it as it changes, and not just past a certain threshold. I'd settle for the first goal for now, though.
