I'm doing an automatic watering project where low power consumption and low cost are important. I'm planning to use YL-69 soil moisture sensors but I have a few questions about them:
1- When it comes to analog reading it looks to my [amateur hobbyist] eyes that this guy actually does nothing. VCC is connected to a 10K resistor, resistor connected to one "leg" of sensor and the other leg is connected to ground. This creates two series resistors: soil + 10K. And analog output is just the voltage at the 10K resistor. So I don't know why I should even pay money for this when I can make something (probably even better quality) with a couple nails and a 10K resistor. I might even be able to get my hands on some galvanized sheets. Is there any reason I shouldn't DIY it?
Specially because I need to minimize current draw as much as possible, and if I'm doing analog reads then the comparator will be drawing unnecessary current. (I'm planning to only turn on the device when I want to measure, but still).
2- Everywhere it is stated the input voltage is 3.3-5v. Now the only real component that this guy has is a LM393 comparator. The datasheet of LM393 says it has an input voltage range of 2-36 volts. So I don't understand where 3.3-5v is coming from. If I decided to use the digital output, is there any reason I shouldn't give this guy 2.5-3 volts? Because I'm planning to use a couple of AA batteries and they're gonna provide somewhere between ~2.5-3 volts depending on how depleted they are.