Wood Water Density Sensor

This is more of a electrical component questions and not a Particle specific one, however a Particle Photon is part of the system. I’m trying to measure the water density of wood while it dries in a kiln. Fresh cut lumber is typically about 40% water content and needs to dry slow and steady to about 10% to be used for indoor projects. Measuring the water density is relatively simple, you just drive 2 nail about 1/4" into the wood and 1" apart. Apply 9-12 volts to one nail and measure the voltage drop. Based on the wood species you can calculate the water density from the from the voltage drop.

I’m using 9 volts across the lumber and then need to reduce the voltage to a safe range to measure by the photon (0-3.3volts). I tried using a voltage divider with a 4700 OHM and 1500 OHM resister to reduce the voltage to 1/4, but this isn’t working. When I measure the output voltage of the wood pin with a meter I see 8 volts. When I run it through the voltage divider I would expect about 1.3 volts, but get 0.

I’ve read about and have tried using an Op Amp with no luck and lots of frustration. Does anyone have any ideas on how to make the voltage divider work or an alternative solution?


Could you also show how you’ve wired the job lot?

Just go with this and you can measure up to 26v.

There is a Particle library for this already.


Thank you! I’m happy to buy a component to solve this problem over building it. I’ll give it a go.


It for sure works, I’ve used these sensors in many different applications.