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.
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.
Step 3: Modification Process
- locate the humidity sensor and remove it using the soldering iron.
- take the plastic cap of an empty plastic box cutter container (that's what I had lying around, but any small gadget will do).
- drill several 1.5 mm holes in 3 sides of this cap: front, left and right side. No need to drill the top or back.
- glue the RH sensor into the cap with a tiny bit of super glue, so that it will hold in place. Do not spill any glue on top of the humidity sensor (the side where the metal contacts show).
- solder 2 wires from the cable to the 2 leads of the humidity sensor.
- solder the other end of these wires to the PCB (Printed Circuit Board) where you removed the humidity sensor. There is no polarity to be observed: it doesn't matter which one is soldered left or right).
- hot-glue the cap to the cable, taking care that no glue covers the sensor element (the metal strips on one side of the sensor) and let the glue cool/harden.
- within the meter housing, guide the new cable so that it can exit next to the temperature probe cable, enlarging the existing hole in the casing with a cutting knife.
- re-assemble the unit and put the battery back in its compartment.
- test to see if it functions correctly by blowing onto the remote humidity probe. This should result in a temporary increase of the RH% reading.