Scientific Oregon WMR300 Temperature and Humidity Sensor THGN300

[mankan]

Trying to get a temperature and humidity sensor THGN300 working. It is connected to the outdoor unit for a Oregon Scientific WMR300 weather station. The rain and wind sensors connected to the outdoor unit is working fine. So I suspect its the actual sensor in the THGN300 that is faulty and to verify this I would need help in identifying the sensor IC first. The IC is marked FEO 11 and is mounted on a small adapter PCB.

Anyone knows what it is?

[ebastler]

This one seems to have the same (unusual) package: Sensirion SHT11. Discontinued unfortunately, but maybe you can find some leftover stock somewhere, or the datasheet helps to find something electrically compatible?

Catalog page: https://il.rsdelivers.com/product/sensirion/sht11/sensirion-sht11-temperature-humidity-sensor-40-c-c/7865551
Datasheet: https://docs.rs-online.com/58dc/0900766b81389d82.pdf

Edit: Sensirion recommends the SHT40 as a successor product. I have not checked whether it is directly compatible (electrically, the package is obviously different).

https://sensirion.com/products/catalog/SHT11/
https://sensirion.com/products/catalog/SHT40/

[mankan]

After removing the weather protective rubber I could measure the PCB and it all fits with the SHT11 datasheet. However I found that 3 of 4 PCB traces had corroded severely and VDD trace was broken. Now that I've repaired the traces with some wires, the next step is to verify the sensors function with an MCU.

SHT11 uses a proprietary 2 line serial protocol and SHT40 has I2C so that would require an MCU with some translation SW to get it backwards compatible with the outdoor unit. However it costs less than 3€ when one SHT11 including shipping would set me back €85.

[mankan]

I found SparkFun SHT15 modules for €40 which I bought and used as donor to the board. Works fine with Arduino at least. Will be a few weeks before testing in the weather station can be done.

[mankan]

Forgot to report back. The temp and humidity sensors are now working fine in the weather station.

[rocchino.palcera]

Hi, i have the same problem. Can You share me the solution adopted? What modules i have to buy? thanks in advance.

[mrcurlywhirly]

FWIW... if anybody is interested in keeping the external temp/humidity on their WMR300 running, I had a similar problem.   My station started transmitting HHs, 100% humidity,  and crazy high temperatures from the external unit.  Resets failed to resolve it....so.   

This may or may not fix your unit, but then - who cares, as this is not functional ..anyway, Proceed at your own risk, and if the PCB moisture protection is required then you will have to improvise.

Obviously you will need a soldering iron, phillips head screwdriver, solder sucker or solder removal braid, some isopropyl alcohol, decent solder, multigrips or a PCB clamp (or somebody gullible enough to hold it while you solder).   

Pull the rj11/12 cable (looks like Rj12 with 5 cores connected to me) out of the enclosure, then disassemble the shield and the unit, pop off the plastic temp/humidity chip cover from the PCB (it will get in the way), and check the chip and its terminations look OK - mine looked fine.  If so check the cable terminations, carefully peel the clear plastic moisture protection layer away from the cable terminations, enough to safely pull through some of the cable, as if it is like my one then probably requires trimming.
 
There are five connections to the PCB, cable looks like rj12 with red - white - yellow - blue - black cores.  I noticed some severe oxidization of the solder on a couple of connectors, so desoldered those then cleaned up the terminations with IPA, trimmed around 10mm off the cables, and carefully cleaned and retinned then reconnected the cores. The job is more fiddly than technically difficult, I enlarged the PCB holes slightly - very carefully,  with a pin.
To test whether it was resuscitated, i have a couple of small zip ties holding the moisture barrier in place, thats a temporary fix.  I suppose it could be siliconed.
Once reconnected, hit the reset in the weather station enclosure, and wait a few hours.. Mine eventually started to transmit again, registered a few 39.6 degree readings when it was about 22c, then settled into normal activity, which it has maintained for a week now. 

FYI - There are alternative temp/humidity boards available using BME280, in 3.3 and 5v, though some hacking would be required if you go down that path with the WMR300.