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 them, how do you set them correctly?

To answer this question, you first have to understand how it works and for what purpose you want to use it. One problem remains: the moisture is only measured at one point in 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 with greenhouses or (raised) beds it works wonderfully, because with these the watering is evenly distributed over all plants and is localized

To do this, simply insert the soil moisture sensor into the soil so that only the part with the cable connection end is visible. The spot must be enclosed by the irrigation and is then representative of all plants.

Function:

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

One LED per input shows the status. The adapter is designed for use with the SMT50, which has 0..3,3V as a signal output. The A2D converts the analogue signal as a digital switching point.

Connect:

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

These are central to that OpenSprinkler connected:

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 (green) is not connected.

Settings sensors:

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 in the sensor settings - we want to water when it's dry, not when it's wet.

The switch-on and switch-off delay is important: Since the sensor also gets wet during watering, the watering would be stopped 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 per program. In my case it is every four hours. The soil moisture sensor then prevents the large number of waterings when the soil is wet. This means that much less watering is used than is set. Only when it is so hot that after four hours all the water has evaporated, only then is it watered again directly.

If it rains or the sun just doesn't shine, the soil stays moist and there is no watering.

A2D Setting:

In principle, you simply start turning the potentiometers until the light goes 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 back until the light (signal) lights up continuously. Glowing means “wet”. 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 does not light up -> readjust until the signal comes on again
• If the ground is dry, but the signal lights up -> readjust until the signal goes out
• When OpenSprinkler on days that are not so hot Waters at all intervals because the signal is not lit, then you should extend the watering duration
• When OpenSprinkler only very rarely waters, then you should consider reducing the watering time.

Occasionally the LEDs will 'flicker' when the humidity is in the transition zone. The switch-on and switch-off delay helps here that the signal is not activated umpteen times. This is normal and cannot be prevented.

Questions? tips?