Moisture probes in general

Looking at your " Wireless Soil Moisture Sensor Long Range IoT Transmitter"

How long is that probe?

Do you have a probe like with a 4-20mA out?

1 Like

The probe length is 10cm and the probe wire length is 3M.


A follow-up question about PR55-2B Wireless Soil Moisture Sensor Long Range IoT Transmitter: is the default number for the “moisture” value in the sensor message payload a number representing voltage, percentage VWC, or what is the range and units here?

the voltage.
0 to 1.1V VWC= 10V-1
1.1V to 1.3V VWC= 25
V- 17.5
1.3V to 1.82V VWC= 48.08V- 47.5
1.82V to 2.2V VWC= 26.32
V- 7.89
2.2V to 3.0V VWC= 26.32*V- 7.89

if you are planning to purchase a new unit, it will also calculate the moisture( real VWC), temp and EC.

1 Like

Hmmm, thanks @Bhaskar . My PR55-2B is reading around 0.5 - 0.75, but then during a drip-watering of soil, it jumps to 100. This is strange, both in terms of the number and the sudden jump from near-zero to 100. I will post a separate issue on this.

Also note that the new PR55-57D does not appear in the catalog when searching for “moisture.”

It also does not show up in the category.

Does NCD have other soil moisture sensors in the Industrial line that I may have missed?

The PR55-2B – are you displaying the VWC or voltage ?
The the water drip is right next to the sensor probe then it could jump quite a bit. make sure probe is all the way in the soil and has soil all around it.

VWC in PR55-2B is – It’s the volume of water divided by the volume of wet soil. Water fills into the air pores of the medium and so your wet soil can have the same volume as the water, and thus can reach near 100%…

In PR55-57D – its ratio or water and soil. bit easy to understand and relatable.

Theoretically real VWC cant be more than 60%.

PR55-57D is somewhat a new device and currently only used by large scale growers. we also have few other soil probes like soil pH , Soil EC, soil NPK.

You have enough exp with ncd device so i believe you will be bale to use PR55-57D in no time. If you need one let me know, can get you one at a discount :slight_smile:

1 Like

@Bhaskar My PR55-2B is displaying the “moisture” attribute which I believe by default is actually voltage, correct? The probe is correctly inserted into the soil. I have a similar probe for a Vegetronix moisture meter that I use in the same way.

While I can understand the sudden jump in the number, why would the sensor report 0.72 and then suddenly 100? Surely it is not recording 100V.

can you share the raw adc values ?

@Bhaskar Hmmm, how do I obtain the raw ADC values? The value attributes in the message payload include: battery_level, moisture, node_id, rssi, transmission_count, and type.

If I need to reconfigure the PR55-2B I’ll do this later in the week as I am away from the gateway for a few days.

@TravisE_NCD_Technica what kind of data the MQTT sensor sends ( in case of soil moisture sensor) ?

This is the parsing code for the soil moisture sensor running in all Gateway devices(excluding IoT Edge):

      if(len < 13){
        return false;
        json["Type"] = "Soil Moisture Sensor";
        json["SKU"] = "PR55-2B";
      uint16_t raw = ((data[9]<<8)+data[10]);
      if(raw >= 870){
        dataObject["Moisture"] = (float)100.00;
        dataObject["Moisture"] = (float)(raw/870.00);
      rDevice = true;

can we modify the firmware to send raw value as well.

also when you get a chance add support for sensors type 69
Wireless 1 Channel Soil Temp Moisture and EC Sensor

data breakdown

Aha, that explains the 100.0 value. So, if the raw value is over 870, it’ll always be 100.
@Bhaskar it’s important to note that, the Moisture value will otherwise always be between 0 and 1 (not 0 to 3.0), and it’s not the voltage as described in the comment above (Moisture probes in general - #4 by Bhaskar) , right? The calculation seems to just be raw / 870.0.

raw value will be between 0- 1024. its the raw ADC value .
The ADC is 10 bit so in order to convert raw value into voltage we will multiply buy 0.00322.

@Bhaskar Do we need to update the parser for this sensor to provide the raw ADC value in the telemetry? If so let me know, I can make that update, then @ybakos can update his gateway.

@Bhaskar I had an error in my response, which I edited. You will know best. But then:

  1. What real-world concept does the raw value represent?
  2. Why do we divide it by 870.0 ?

The data payload for Moisture, dataObject["Moisture"], will always either be 100.0 or some value between 0 and 1 (raw divided by 870). So then, what does this dataObject["Moisture"] value represent? 1/870 is 0.001149 and not 0.00322, so it does not seem to be voltage…

My apologies if I am misunderstanding! :slight_smile:

@TravisE_NCD_Technica it will be good idea to add raw value. while you are at it, also add support for type 69.

  1. raw value is actual adc value outputted by the soil sensor. You can use it to convert to voltage and the calculate VWC.
  2. from our test we found out that when probe is dry the raw value is around 0 and when its all the way in water the raw value is around 870. The new probe from same manufacture now could have raw value around 930 when its all the way in water.
    using this range we can divide the scale from 0-100%.

Keep in mind probe does not output full 3.3V when its completely submerged in the water. It outputs somewhere around 2.8V that why we use 870 value.

here is a simple test. put the probe in water ( halfway ) and it should output around 50%.

PR55-47D does all the calculation inside and directly outputs final results.

The raw ADC value is 870 when fully submerged in water. So if you take the reading and divide it by 870 it provides a percentage. So if the soil moisture were 50% for example that would mean that the raw ADC value would be 435. If you divide 435 by 870 you get 0.50 so any value you get back multiply by 100 and that will give you the actual percentage(I probably should have just done that in the parsing routine.

I will update the firmware this afternoon to provide the raw ADC value and also multiply the moisture value by 100 so it comes in as a percentage.

I will let you know when the firmware is updated on our repo and you can update your MQTT Gateway.

1 Like

Thanks @Bhaskar and @TravisE_NCD_Technica for the explanation. It makes sense now.