I am working on an old Dehumidifier with a built in humidity sensor. This sensor has three wires coming from it: Red, Black, and White. Experimenting I connected the Red-3V3, Black-Ground, White-A0 pin. Now I am reading the pin. It reads an output of 10 in this relatively low humidity room, and 1250 when I breath onto it. Any ideas of what this old sensor is reading/digitizing? Or how to convert?
It is a “SANGSHIN” sensor.
@Dsradley5, do you have a picture of the sensor?
from the pic it looks like this one:
https://www.acalbfi.com/uk/Sensors/Humidity/p/Humidity-Sensor--20-95--RH--5--Accuracy--0-60C--0-5VAC--KSH-02BJL/0000006PIR
KSH-02BJL humidity sensor is a high quality, highly responsive polymer film humidity sensor. At ambient temperature the sensor resistance drops from 30%RH to 90%RH in approximately 1.5minutes.
could it be?
I searched on google for sangshin humidity sensor and from the pictures, I found one similar to yours
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Yes, that appears to be the one i have.
@gusgonnet that may or may not be it! That humidity sensor has two wires but requires 5 VAC! I’ve not interfaced with one of these before but their apparent resistance varies with the frequency applied and the humidity. Perhaps @bko might have some insights.
The device north of it looks like a thermistor. So they appear to share a common (GND?). @Dsradley5 will need to take resistance measurements to characterize the thermistor. Not sure what to do with the humidity sensor.
I have not used one of these before either. From the linked datasheet, it looks like you are supposed to feed the sensor 1V AC at 1 kHz and it will vary its resistance over a range of 5.5Mohm to 1.9kohm so the current will be 0.18uA to 526uA and you can measure that to get %RH.
It looks like a purely resistive device so I suppose you could use a constant current AC source and measure the voltage instead.
@bko, I suspect the second approach is what is used. Not a friendly sensor to use with Particle devices IMO.
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