I’m working on a T3000 home automation system that has many functions but some rain tank levels and demand irrigation. Has anyone experimented with soil moisture using a resistive input? I’m going to experiment with it so I can write a demand based watering system using some kind of probes like this
These will need some electronics to make them work well, I’ll be you can search and find one with a 0-10V or 5V output.
Aaron,
Keep us posted on this. I have a setpoint adjustment on a system that I have not been able to get it to work as desired and it also is just a variable resistive device. I was told I could measure the voltage and use that but was not successful after several attempts. Maurice’s reply to your application makes it sound like a resistive input is not supported but a temperature sensor using a 10k thermistor is supported and I have many of them working.
If you are not able to get the resistive input to work, set an AO to 0-10vdc and set it to 100% in software so you can use it as a power supply. Then add a resistor in line with your device where the value of the inline resistor will limit the current on your power supply and ideally be equal to the probe expected value (I would say at least 10k; if you have lower resistance, then maybe set the output to 50% and use 5vdc). Then connect the controller input ground, output ground and one side of the probe together. The other side of the probe, inline resistor and plus side of the input together and finally the inline resistor to the “power supply” (AO positive). That gives you a basic voltage divider at the input.
When you have a low resistance at the probe, you will see a low voltage at the input since the higher inline resistance will cause a larger voltage drop and when you have a high resistance at the probe, you will see a higher voltage at the input since the voltage drop at the inline will be reduced.
I have done this type circuit with other manufacturers but not on a Temco controller so maybe test the input/output common connection by using a 100k or 1m resistor between them the first time. If they are both truly ground, there will be no current so no difference with or without the resistors. IF one of them has a diode or some circuitry between the terminal and ground where connecting the input and output may be a problem, the resistor will be a current limit to try and prevent any damage.
Let us know if you get this working with just a resistive circuit as my problem is already wired in 80 places above ceiling tiles so I am hoping there is a way to configure an input to read resistance the same as if it were a 10k sensor but different values.
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I will try to get a resistance reading on wet and dry soil here, or i like your 10vdc source idea and i can measure a voltage back through the wet soil maybe
… Maurice, in the T3000 software, can a custom table be made on resistance or only a 10vdc input?
The universal inputs on our controllers uses a 10k weak pullup resistor tied to 3V. This allows it to sense typical 10k thermistors and other passive resistances in this range. The soil meter on the other hand will vary in the Mega ohm range. Also proper commercial soil meters will switch the diriving signal from one terminal to the other to avoid electrolysis.
Here’s a couple decent looking meters on Aliexpress with 0-10V outputs, I will get my crew to buy a few, we’ll test them out and report back here in a week. RS485 version might be useful too for long runs, we’ll try both.
I just ordered this 0-10v one and I will report back. It says they make it 0-10, 4-20 and rs485
I may also lay out a small pan with a small cheap float switch in it. If it rains, the pan will be full and the switch will be tripped and it won’t water that day. If it has been hot and hasn’t rained in a few days, the water will evaporate and the switch will switch and the system will water that day.
There used to be a cork sensor on the market that we used for sprinklers at some of the commercial buildings we did (decades ago) and worked like your float switch idea. The sensor was mounted where the rain or sprinklers would hit it and the cork being wet would swell and make a contact so the next day, if the contact was still made, we skipped the sprinkler routine and saved the water.