I visited our local home improvements store and found a 3M dehumidifier model which can be hooked to a water pipe. No more emptying the water tank! Unfortunately, there was still the problem of restarting the machine manually, as it would only run for 16 hours at a time.
I took care of this using our TPS2L device. This product belongs to the Tibbo Project System (TPS) family. The TPS uses Tibbits, which are I/O modules houses in color-coded plastic shells.
To "push buttons" on the machine I used Tibbit #3-1. Each such Tibbit has a pair of low-power relays. In my project I am "pushing" two buttons -- "power" and "mode" -- so a single relay Tibbit is sufficient. Relays are connected in parallel with the real buttons of the dehumidifier.
To sense the machine's state I used Tibbit #4-1 (two opto-isolated inputs). I sense the state of a single LED -- "high speed". The LED side of the opto couple inside Tibbit #4-1 is wired in parallel to the "high speed" LED on the dehumidifier's panel.
I also plugged in Tibbit #10 (12V->5V power regulator). Wires are connected through the Tibbit #20 (9 terminal blocks).
The hardware configuration for the TPS2L system can be found here (scroll down to find the "3M_dehumidifier_control" project): www.tibbo.com/buy/tps/tpc.html
I used the more expensive TPS2L device (with the LCD and keypad). You can run the project on the TPS2, which is much cheaper. The LCD and keypad are there for my future enhancements.
The corresponding Tibbo BASIC project is here: www.tibbo.com/basic/resources/dehumidifier_control.html
Step 1: Open the Dehumidifier
Open the dehumidifier while observing the above precautions.
Locate the keypad.
Step 2: Pull Out the Keypad PCB
Step 3: Connect the Wires in Parallel With Buttons and LEDs
Step 4: Optional: Print the Plastic DIN Rail Section
I used my Replicator 2 to print out a "plastic DIN rail" section (I've included the STL file here).
The TPS2L now attaches to the machine's side.
Step 5: Simple Tibbo BASIC Code
My project uses the feedback from a single LED ("high power") to make sure that the dehumidifier is on and is running in the correct mode. There are three operating modes in total. To get to the correct mode the code "pushes" the power button, then "pushes" the mode button up to three times. If the "high power" LED does not light up after any of these steps the program will "push" the power button again, and then the mode button up to three times. The logic here is that maybe the first time the power button is pushed the dehumidifier actually gets turned off.
Step 6: Future Plans
The next (and very obvious) step will be to install the humidity/temperature sensing Tibbit and turn the dehumidifier on and off as necessary.
After that I plan to hook this up to an AggreGate server and enable the remote monitoring and control of my dehumidifier.