Looking at  the schematic for the controller, it consists of no more than a Microchip PIC 16F873, a  rotary encoder with integral pushbutton and of course the SHT sensor.

The Sensirion sensor requires two pins from the PIC, one for bidirectional data and the other for the clock signal. If you use the Parallax part for this sensor, the pull up resistor R4 should be omitted as this is already on the Parallax carrier board.

In parallel with the three trip outputs are indicator LED's to show which output is active. The trip parameters are entered via the rotary encoder, this was used for two reasons,

1. Only one hole would need to be drilled in a box, and;
2. I liked the idea of 'dialing' up the settings. The pushbutton is used to select menus.

The mechanical rotary encoder is a 2-bit incremental type and produces a binary GRAY code output (see panel). The Piher C1-11 encoder has 30 pulses per revolution, as the software only needs to detect clockwise or anti-clockwise information, this can be substituted with almost any encoder you may have lying around.
If you are lucky, that old discarded wheel mouse lying in the junk box may just use a rotary encoder, of course, you'll then need a separate pushbutton switch . Whilst an encoder with a lower pulse/revolution can be used, don't be tempted to use one with higher pulses, you will need to experiment with the size of the knob or drive yourself mad trying to dial in the right data.

Connector JP3 is for in-circuit programming, D1 isolates the ~13V programming voltage from the 5V circuitry during programming, resistor R5 keeps the PIC out of reset during normal operation. If you wish to attach a reset button then you can add one between D1 and ground. R1-3 are the pulldown resistors for the encoder, the encoder pulling the PIC pins high as they are activated. JP1 the LCD header connects to a standard LCD with VR1 the backlight control. JP2 is brought out to a header and is spare. JP4 carries the switched outputs signal.

Heater is the under temperature switch, Humidity for under humidity and OverTemp is -- well for over temperature. As this controller is not really a true closed loop type you can control the window of temperature that is measured. The over temp trip can be no more than 10° above the undertrip temperature setting.

The power supply is standard with a 12V take off point that could be used for the DC controller board. The input to the bridge rectifier can be either via a plug pack or the AC board.

To DC board

Gray Code