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The humidity sensor in my Oregon Scientific Weather Station (BAR208HGA) is stuck at 27% in vastly varying conditions. Having declared it dead, I'm looking for a replacement. (Edit: indoor unit; sat on my desk and suffers from old age.)

The white square at the bottom with interlaced traces and a "3" is the humidity sensor. Edit: back side is unmarked. Its legs are connected to 1.5K and 1.5M resistors (by measurement, not color code) above, and then the 1.5K side takes off to an epoxied chip.

Oregon Scientific BAR208HGA Sensors

Digikey shows 2 pin sensors reporting in pico-farads, and in ohms impedance @ 1KHz. Pricing is ~US$6 (and way up) in 1K quantity. Most are polymer based.

Newark has some MULTICOMP HCZ-H8-B (from Europe) at US$0.63 in 1K quantity. These are Polymer on Alumina substrate. Might mine be a previous generation???

Perhaps what I have is ancient and/or Chinese, so not in the current parts catalogs.

Does anyone want to guess at the specifications for my broken sensor?

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  • \$\begingroup\$ Have you tried just reheating every solder joint with some leaded solder? \$\endgroup\$ – winny Dec 9 '17 at 7:48
  • \$\begingroup\$ @winny looks like he tried that at least once. \$\endgroup\$ – Spehro Pefhany Dec 9 '17 at 22:36
  • \$\begingroup\$ Sorry... What you see is Chinese manufacture ("Made in CHINA" on the label, you choose ROC or PRC) at least 5 years, probably 8 years old. All I did was pop off the back to take a picture, and gently lift the sensor to check the back. Afterwards, I followed a couple of the traces from the sensor, measured the two resistors on the right, and wrote the post. What you see is what I got from Oregon Scientific. \$\endgroup\$ – HiTechHiTouch Dec 10 '17 at 2:12
  • \$\begingroup\$ @HiTechHiTouch Interesting. A grotesque amount of solder on those connections. Maybe manually dip soldered (badly) in a pot- I would expect wave soldering to be much better than that, even if badly adjusted. It does not aid the reliability. \$\endgroup\$ – Spehro Pefhany Dec 10 '17 at 18:12
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The board was obviously made in Asia - China or Taiwan probably, with some pretty gnarly touch-up by someone. Did you actually get it wet?

I think it's a pretty long shot to find the specs of an unmarked unit unless you could source a spare part from the manufacturer, however there is something you can do.

Remove the sensor, clean the board with pure isopropanol (not drug store rubbing alcohol) if it got wet and allow it to dry. Then replace the sensor with various (known) capacitors and combinations of capacitors in the tens of pF and note the readings- you will quickly discover the scaling and you can figure out which, if any, is a reasonable sub. These things are not typically all that accurate, a few percent would be good. You can always trim it a bit at one point with a fixed of variable cap.

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  • \$\begingroup\$ Interesting idea! I will definitely give it a try, though I can't say when. PS: Unit always stayed indoors on my desk. It's also a receiver for outdoor stations. \$\endgroup\$ – HiTechHiTouch Dec 9 '17 at 22:27

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