SDI-12 Soil Moisture Probe Help

[robert-hh]

@Bryan-Hom Sorry, I misread you diagram. Pin A has to be at a level between 0 and 3.3 V, like 1.8 V in the first diagram. You asked from where to get it, I recommended an 1.8V regulator which in turn gets it power from 5V or 3.3V. For a fist test, you should also be able to use a 1.5V battery.

[Bryan Hom]

@robert-hh Thank you! i rigged up the battery and got the response. I also just tried used a DAC output on Pin22 set at 55% which is roughly 1.77V and it seems to work as well without any special power supply

dac = machine.DAC('P22') # create a DAC object
dac.write(0.55) # set output to 55% ~1.77V

[Gusti Made Arya Wijaya]

@Bryan-Hom @robert-hh Hello, I've tried the program and do the wiring diagram like this
but it still can't seem to get any reply from the sensor. ,

here is my program

import utime
from machine import Pin, UART, DAC
# from machine import UART

uart = UART(1, baudrate=1200)
p_tx = Pin('P10', mode=Pin.OUT)
p_dir = Pin('P11', mode=Pin.OUT)
pin12 = Pin('P3', mode=Pin.OUT)
dac = DAC('P21') # create a DAC object


def SDI12(cmd):
    uart.deinit()
    p_tx.value(0)
    p_dir.value(1)        # set output dir
    utime.sleep_us(12800)  # send BREAK
    p_tx.value(1)
    utime.sleep_us(8333)   # send MARK
    uart.init(1200, bits=7, parity=UART.EVEN, stop=1, timeout_chars=75)     # init with given parameters
    uart.write(cmd)       # send command
    utime.sleep_us(8333 * len(cmd))  # wait to send command (byte time * command lenght)
    p_dir.value(0)    # output set to read
    line = uart.readline()      # read data from UART
    return line;

while True:
    print("reading")
    pin12.value(1)
    dac.write(0.55) # set output to 55% ~1.77V
    utime.sleep(2)
    line = SDI12("?!")
    utime.sleep(3)
    print(line)
    # pin12.value(0)
    utime.sleep(10)

I need your help to fix it, Thank you

[robert-hh]

@Gusti-Made-Arya-Wijaya Compqring with the port of the previous poster, you use different pins for p_tx. In the previous post, p_tx is the same a UART 1 TX, and that is by intention.

[Gusti Made Arya Wijaya]

@robert-hh @Bryan-Hom Hello, I've updated the program like this

import utime
from machine import Pin, UART, DAC
# from machine import UART

# uart = UART(1, baudrate=1200, pins=('P10','P11'))
uart = UART(1, baudrate=1200)
p_tx = Pin('P3', mode=Pin.OUT)
# p_tx = Pin('P10', mode=Pin.OUT)
p_dir = Pin('P11', mode=Pin.OUT)
# pin12 = Pin('P3', mode=Pin.OUT)
dac = DAC('P21') # create a DAC object


def SDI12(cmd):
    uart.deinit()
    p_tx.value(0)
    p_dir.value(1)                                                          # set output dir
    # utime.sleep_us(12800)                                                   # send BREAK
    utime.sleep_us(14000)
    p_tx.value(1)
    utime.sleep_us(8333)                                                    # send MARK
    uart.init(1200, bits=7, parity=UART.EVEN, stop=1, timeout_chars=75)     # init with given parameters
    uart.write(cmd)                                                         # send command
    utime.sleep_us(8333 * len(cmd))                                         # wait to send command (byte time * command lenght)
    # p_dir.value(0)                                                          # output set to read
    line = uart.readline()                                                  # read data from UART
    return line;

while True:
    print("reading")
    # pin12.value(1)
    dac.write(0.55) # set output to 55% ~1.77V
    utime.sleep(2)
    line = SDI12('?!')
    utime.sleep(3)
    print(line)
    # line = SDI12('0M!')
    # utime.sleep(3)
    # print(line)
    # pin12.value(0)
    utime.sleep(10)

but the response is still "none", and I use rs485 module like this (max485)

[robert-hh]

@Gusti-Made-Arya-Wijaya As far I see it, the chip has both transmit enable DE and receive enable /RE. For Transmit, the DE has to be high, for receive, the /RE has to be low. Unless you have an inverter connected between DE and /RE, you have to control both in software.

[Gusti Made Arya Wijaya]

@robert-hh I've followed the wiring by @AntonioValente's reply in https://forum.pycom.io/topic/1924/sdi-12/6 he uses SN65HVD1780 chip that has same pinout as MAX485.

[robert-hh]

@Gusti-Made-Arya-Wijaya But still you have to control both DE and /RE. You code seems to control only one of them.

[Bryan Hom]

@Gusti-Made-Arya-Wijaya

Here is my code. You may also have issues with your board. i would recommend the sp3485 chip as that is what i am using

def SDI12(cmd):
    uart = UART(1, baudrate=1200)
    p_tx = Pin('P3', mode=Pin.OUT)
    p_dir = Pin('P11', mode=Pin.OUT) #RTS pin on rs485 breakout board
    dac = machine.DAC('P22')        # create a DAC object for rs485 board to be used as reference voltage for terminal A
    dac.write(0.50)   # set output to 50% ~1.59V Note: if this voltage output is greater than 1.77, the sensor will no longer read

    uart.deinit()
    p_tx.value(0)
    p_dir.value(1)                                                          # set output dir
    time.sleep_us(12500)                                                   # send BREAK
    p_tx.value(1)
    utime.sleep_us(8333)                                                    # send MARK
    uart.init(1200, bits=7, parity=UART.EVEN, stop=1, timeout_chars=75)     # init with given parameters
    uart.write(cmd)                                                         # send command
    time.sleep_us(8333 * len(cmd))                                         # wait to send command (byte time * command lenght)
    p_dir.value(0)                                                          # output set to read
    line = uart.read()                                                      # read data from UART
    return line;```

[robert-hh]

@Gusti-Made-Arya-Wijaya Did you connect both /RE and DE to the p_dir Pin?

[Gusti Made Arya Wijaya]

@robert-hh yes I did

[Gusti Made Arya Wijaya]

@Bryan-Hom oh okay thanks for your advice. I only have max485 and max3485 now