Instructables

Digital Temperature/Hygrometer modification

I have a temperature/RH (Relative Humidity) meter which reads the inside temperature and humidity. An outside wired probe measures the outside temperature.
Since I needed to know the RH in my "wine cellar" refrigerator (where I ripen my homemade cheeses), I needed an outside probe for measuring the RH.
This instructable describes the easy steps it takes to accomplish this.
 
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Step 1: What you need

- digital Thermo/Hygrometer.
- a length of (preferably) shielded cable (e.g. from an old PS-2 mouse).
- cap of empty cutter blades box (see pic in step 3, anything similar will do).
- drop of super glue (10 seconds glue).
- soldering iron.
- hot glue gun.
- small screw driver.
- cutting knife.

Step 2: Preparation

- begin by taking the battery out of its compartment.
- turn around the thermo/hygrometer and remove the back cover.
- find an unused PS-2 mouse and remove its cable, cut of the PS-2 connector. Any other thin cable with 2 wires will do. If more than 2 wires, cut off the extra ones.
HoldOnTight3 years ago
Wow, good job. Can you comment about the accuracy change before and after adding the extra wire? Your initial photo showed 50% RH and then, I saw another that said 65%. I believe adding the wire added capacitance to the sensed input, and as a result, the RH reads (15%) higher. To improve accuracy, you could recalibrate the meter or you could shorten the wire as much as possible.

I like your idea and I'm going to try to do this project!!

Thanks for the 'ible.
memkuk (author)  HoldOnTight3 years ago
Sorry for the very late reply. I actually started checking the accuracy after I made the modification, using one of those wet/dry double bulb thermometers, from which it is possible to calculate the RH %. I hope you know what kind I'm talking about, because I had never heard about it myself before either. It turned out to be pretty accurate, at least for my purpose (cheese ripening and curing meat). Maybe its accuracy is also due to the fact that the wire I used to make the modification is very well shielded.

Take care.