A2D + SMT50 and now?

Our new A2D adapter together with the SMT50 soil moisture sensor is becoming increasingly popular. But how exactly do you use these and how do you set them correctly?

In order to answer this question, you first have to understand how it works and what purpose you want to use it for. One problem still remains: the moisture is only measured in one area of ​​the garden. This is therefore not recommended for large-area lawn irrigation - the differences are too great due to different soil conditions and uneven water distribution. But it works wonderfully in greenhouses or (raised) beds, because in these cases the irrigation is distributed evenly over all plants and is localized

To do this, you simply have to insert the soil moisture sensor into the ground so that only the part with the cable connection end is visible. The area must be included in irrigation and then represents all plants.

Function:

The A2D has 2 analog inputs, each of which is connected to a trigger via a potentiometer. While the digital inputs on the OpenSprinkler have to be switched to GND in order to switch the signal, the voltage is measured on the A2D. The permissible input voltage is 0..20V. The potentiometer can be used to set the switching voltage from which the OpenSprinkler receives the signal.

One LED per input shows the status. The adapter is designed to use the SMT50, which has 0..3.3V as a signal output. The A2D converts the analog signal into a digital switching point.

Connect:

I use two SMT50 soil moisture sensors in my project garden:

 

These are centrally connected to the OpenSprinkler:

The sensors are of course connected via the A2D.

A2D: from left to right: GND, SN1, SN2, VIN
These are now connected to both SMT-50: WHITE (white) to GND, YELLOW (yellow) to SN1 or SN2 and BROWN (brown) to VIN (or +5V). GREEN is not connected.

Sensor settings:

It should not be overlooked that this is a soil MOISTURE sensor, not a soil DRY sensor. Therefore, you have to activate the “Normally open” option when setting the sensor – we want to water when it is dry, not when it is moist.

The switch-on and switch-off delay is important: Since the sensor also gets wet when watering, the watering would stop immediately. Therefore the switch-on delay must last longer than the program. The switch-off delay should always be greater than the switch-on delay.

Settings program:

In principle, it now works like this: we define a maximum watering level using the program. In my case it's every four hours. The soil moisture sensor then prevents multiple irrigations when the soil is moist. This means that much less water is irrigated than is set. Only when it is so hot that all the water has evaporated after four hours will watering be carried out again straight away.

If it rains or there is simply not much sun, the soil remains moist and irrigation is no longer necessary.

A2D Setting:

Basically you just start turning the potentiometers until the light turns on or off. This “transition point” shows us the current humidity. Now we activate the irrigation and let the program run until it switches off again. Now turn the potentiometer until we find the transition point again, but then turn it back until the light (signal) lights up permanently. Glow means “moist”. For optimal settings we need a hot day so that the moisture evaporates faster. Wait a few hours and then check the soil and judge for yourself:

• If the soil is moist and the signal lights up, ->Ok, check again later
• if the soil is dry and the signal is NOT lit -> check again after the next watering interval
• If the soil is moist but the signal doesn't light up -> readjust until the signal comes on again
• If the soil is dry but the signal is on -> adjust until the signal goes out
• If OpenSprinkler still waters at all intervals on days that are not so hot because the signal is not lit, then you should extend the watering duration
• If OpenSprinkler only waters very rarely, then you should consider reducing the watering time.

Occasionally the LEDs will “flicker” when the humidity is in the transition area. The switch-on and switch-off delay helps ensure that the signal is not activated countless times. This is normal and cannot be prevented.

Questions? Tips?