soil sensor

9 Articles

Vintage Ammeter Becomes Plant Moisture Gauge

August 15, 2020 by 15 Comments

It’s not uncommon to happen across vintage measurement equipment at the local flea market or garage sale. Often with an irresistible aesthetic, and built to last decades, these tools nonetheless tend to be sidelined when modern multimeters are available. [Build Comics] had just such a piece on hand, and decided to repurpose it with some modern hardware instead.

The build begins with a Hartmann & Braun 60 amp ammeter. Replete in a nice wooden box, it’s the perfect candidate for a modern refit. The device uses an indicator of the moving iron type. Intending to turn the device into a soil moisture monitor, [Build Comics] began by removing the original heavy-wound coil. In its place, a custom coil was installed instead, wound on a 3D printed bobbin using a modified sewing machine. This allows the meter to be easily driven by an Arduino with little more than a transistor on a GPIO pin. To detect moisture, a Iduino ME110 moisture probe was used. Complete with cloth-covered wire to maintain the vintage look. The original meter plate was also photographed, modified, and reprinted, to read moisture levels instead of current.

If you’re interested in these gauge restoration techniques but don’t have a green thumb, no worries. [Build Comics] used similar tricks to put together a gorgeous weather station that would look great on your desk.

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A Capacitive Soil Sensor Hack For Lower Voltage Supplies

July 27, 2019 by 24 Comments

A frequent beginner project involves measuring soil moisture levels by measuring its resistance with a couple of electrodes. These electrodes are available ready-made as PCBs, but suffer badly from corrosion. Happily there is a solution in the form of capacitive sensor probes, and it is these that [Electrobob] is incorporating in to a home automation system. Unfortunately the commercial capacitive probes are designed to run from a 3.3 V supply and [Bob]’s project is using a pair of AA cells, so a quick hack was needed to enable them to be run from the lower voltage.

The explanation of the probe’s operation is an interesting part of the write-up, unexpectedly it uses a 555 configured as an astable oscillator. This feeds an RC low pass filter of which the capacitor is formed by the soil probe, which in turn feeds a rectifier to create a DC output. This can be measured to gain a reading of the soil moisture level.

The probe is fitted with a 3.3 V LDO regulator, which is simply bypassed. Measurements show its output to be linear, so if the supply voltage is also measured an accurate reading can be gleaned. These probes are still a slightly unknown quantity to many who might find a use for them, so it’s extremely useful to be given this insight into them.