Micropython HC-SR04 - ESP8266

Question

I am trying to get the NodeMCU ESP8266 dev board to work with an HC SR04 Ultrasonic Sensor. I keep getting a reading of "0", which is not the reality.

I have the ground and 5v pins of the sensor hooked up to a 5v source, and the Echo and Trigger pins on GPIO pin 4 and 5. In theory, everything should be working, but I just keep getting "0". Perhaps there is something wrong with my code? See below:

import machine
import sys
import time
time.sleep(1) #Just for everything to settle down

while 1:

    pinTrigger = machine.Pin(5, machine.Pin.OUT) #defining the pins
    pinEcho = machine.Pin(4, machine.Pin.IN) #defining the pins

    pinTrigger.high()
    time.sleep(0.00001)
    pinTrigger.low()

    time.sleep(0.5)

    start = time.time()
    stop = time.time()

    while pinEcho ==0:
        start = time.time() #Starting the time when sending out the signal

    while pinTrigger ==1:
        stop = time.time() #Stopping the time when the signal comes back

    elapsed = stop-start #working out the time.

    distance = elapsed * 34000 #multiply by speed of sound to get distance

    distance = distance / 2 #divide by 2 becuase it was there and back

    print ("Distance : %.1f" % distance) 

    sys.exit()

Please help.

while pinEcho ==0: start = time.time() is very inefficient and you might miss the time window in which the pin is low. In such cases, one would use interrupts. (see docs.micropython.org/en/latest/wipy/reference/isr_rules.html). The first step to increase performance would be to replace the computation of the start variable by pass (i.e. do nothing), and then compute start when you're out of the while loop. Same for stop. The next thing: time.time() might have a too low accuracy. The speed of sound is incredibly high, and thus you would need to messure in the microseconds — Maximilian Gerhardt
– Maximilian Gerhardt, Commented Feb 23, 2017 at 14:08
range to get accurate results. If time() is in milliseconds, that might be too coarse. Print your stop-start to the console, if it is 0, then your timer is not good enough. Again, you need to switch to interrupts, wait on the FALLING_EDGE event, then save the current time in microseconds, then wait for the RISING_EDGE on the echo pin, save the time, then compute the time difference. — Maximilian Gerhardt
– Maximilian Gerhardt, Commented Feb 23, 2017 at 14:10
What is time.sleep(0.5) for? Why do you make your code sleep 500 msec? — Mert Gülsoy
– Mert Gülsoy, Commented Feb 24, 2017 at 9:01
Have you looked at this thread on the micropython forum: forum.micropython.org/viewtopic.php?f=16&t=2436 ? — nekomatic
– nekomatic, Commented Feb 24, 2017 at 10:52
Thanks so much for all the help guys! @nekomatic - Are these libraries that I refer to in my main.py code, or is this the actual code itself? I'm just trying to figure all this out. — LukeVenter
– LukeVenter, Commented Feb 27, 2017 at 8:25

EvilSocket · Accepted Answer · 2018-07-20 13:43:39Z

1

Here is what solved the problem:

import machine
import utime


while True:
  trig=machine.Pin(5, machine.Pin.OUT)
  trig.off()//stop reading
  utime.sleep_us(2)
  trig.on()
  utime.sleep_us(10)
  trig.off()
  echo=machine.Pin(4, machine.Pin.IN)
  while echo.value() == 0:
    pass
  t1 = utime.ticks_us()
  while echo.value() == 1:
    pass
  t2 = utime.ticks_us()
  cm = (t2 - t1) / 58.0
  print(cm)
  utime.sleep(2)

Elsewhere on the internet they suggested that you put a resistor inbetween the echo and the pin on the NodeMCU board (ESP8266), This made the measurements trip out pretty badly. So right now I have it working 100% with 5v and Ground (to the HC-SR04) connected to my RPi GPIO, and the trigger and echo connected to the NodeMCU board pins.

Another thing to note is that I was doing readings at 1s, (last line of the code), changing that to 2 seconds made the code a lot more accurate.

Hope this helps someone.

Here's the diagram:

Working Diagram

edited Jul 20, 2018 at 13:43

EvilSocket

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answered Mar 3, 2017 at 11:11

LukeVenter

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3 Comments

Alex Shroyer Over a year ago

I wouldn't advise people to connect a 5v-powered device to something which is only 3.3v-tolerant, but the general approach is very good. On my robot, I started with this code, then made it a separate function and added timeouts to each of the while loops. Mine is using a 1k resistor inline with the Echo pin. Seems pretty robust.

LukeVenter Over a year ago

So happy that this helped you. Would love to see your project!

Paul Allsopp Over a year ago

"while True: trig=machine.Pin(5, machine.Pin.OUT)" You are assigning the pin every time you loop. Make the pin assignments outside of your loop

vaheeds · Accepted Answer · 2019-08-09 10:48:18Z

0

Take a look at this library to get it easier to work with HC-SR04 Sensor driver in micropython.

answered Aug 9, 2019 at 10:48

vaheeds

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