I was thinking it would be interesting to make a LoRaWan timber
moisture meter. The theory is to apply some volts (10v?) in order to measure the resistance between two
pin probes in the timer, the moister the wood the lower resisance.
As I understand it the resistance for this type of application is measured in megohms, are there any module out there that can measure resistance as an analog value, GPIO? Or is there some other way of more acuratly measuring the resistance ohms?
I also see that many of the hand held timber moisture meter send out 10v into the wood, is a buck converter the way to go since I was planning on using some sort of 3.3v battery driven device? Will amps on the pins factor?
Was planning to put the device in deep sleep waiking it a couple of times a day to get a reading and send it through TTN.
hehe, I think the most common use for this type of sensor would be mounted inside walls where the sun dont shine.
e-peas.com do have some sort of energy harvest chip thingy from RF sources wi-fi, GSM900, 3G, ++ combine that with some supercapasitors you could LoRaWan timber moisture in walls for all times. Must figure out power requirements of this device first…
Well, you cannot directly measure resistance, you need to apply a voltage to the ‘resistor’ and measure the current flow or the voltage that current develops across a resistor.
However looking at the chart the resistances to be measured seem to range from 700,000MegOhm to 0.07MegOhm
I would suggest that measuring such a wide range of resistance is a non-trivial exersize.
If you exclude the out layers for the hard woods at very low moistures it is not that bad, then again it would be nice to measure down to 7-8% moisture a typically a requirement when wood is used in furniture production.
Looks like i need to do some reading up on my ohms, volts and amps…
A couple of thoughts: Resistance soil moisture sensors don’t have a good reputation due to corrosion with the applied current. I have a vague recollection of someone using a capacitance soil moisture sensor for measuring tree or wood moisture. So that may be a better but more expensive option. If you do use a resistance sensor, one thought I had was to reverse the polarity for each reading, using an H-bridge, to minimize corrosion. But I haven’t tried that.
How far apart are the electrodes in the 10V systems? You could always move them to 1/3 of the spacing for 3.3V.
Actually have one of those Capacitive Soil Moisture Sensors laying around here somewhere, I will give it a go and report back. I wonder how deep into the timber they penetrate and to what degree temperature, species, density ++ will effect results. Only one way to find out
Love the idea of reversing the polarity with an h-bridge, corrosion is an defiantly an issue with the resistance sensors. I have seen some people suggesting graphite probes for soil monitors to avoid corrosion, but I think there might be some issues jamming a couple pencil leds into a piece of oak.
Thank you for the tips, will let you know how it goes
