A kit?

Subject: [New post] Analog soil moisture alarm
From: "Hack a Day" <donotreply@wordpress.com>
Date: Fri, 22 June, 2012 6:01 am

Post : Analog soil moisture alarm
URL : http://hackaday.com/2012/06/22/analog-soil-moisture-alarm/
Posted : June 22, 2012 at 5:01 am
Author : Mike Szczys
Tags : analog, moisture sensor, op-amp, soil
Categories : green hacks

http://hackadaycom.files.wordpress.com/2012/06/soil-moisture-alarm-e1340298723229.jpg

The lion's share of soil moisture monitors we see are meant as add-ons for a microcontroller. So we're glad that [Miceuz] tipped us off about this soil moisture alarm he built with analog parts (http://wemakethings.net/2012/06/21/plant_watering_alarm/) . It's really not hard to take the concept and build it in the analog world. That's because you're just measuring a resistance value. But for those of us who never really got started with analog parts this is a great project to learn from.

A high-efficiency op-amp is doing the brunt of the work. When the soil is moist the resistance is rather low compared to a reference voltage provided by a separate resistive divider. But when the plant gets thirsty and the soil dries out the resistance increases, triggering the op-amp to illuminate an LED and create some noise on the buzzer (we're a bit confused on how that buzzer works).

Unfortunately this isn't a viable long-term solution as the battery calculations show it lasting only about four months. That's where a microcontroller-based circuit really shines, as it can put it self in low-power sleep and wake infrequently to take readings.

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