Displays and Transmits RF messages of measurements of certain gases

This device measures the local air for traces of Carbon Dioxide (CO), Methane (CH4) and Liquid Petrolium gas (LPG). It is more sensitive than those alarms commonly sold for household use. It cannot discriminate between these gases, and it also seems to respond to cooking vapors and solvents.
It also measures ambient temperature and light.
The measurement results are displayed on an LCD backlight display and are transmitted in two RF messages.
It is self contained and has a line-operated switching power supply. It uses a 2 row by 16 column character LCD display.
It consists of four sub-assemblies which are housed in a transparent plastic case with a sturdy base and a closely-fitting top, intended for foods. All structural elements are made from aluminum extrusions.
The Base Frame sub-asembly attaches to the plastic base by two screws.
The Base Frame is fastened directly to two of the other three sub-assemblies: the Sensor Board and the Display. The Main Board connects to the Display.
The number of fasteners and electrical connectiond are minimised

A. The Base Frame sub-assembly includes the power supply and a speaker. It has a line cord, three DC output pins for the plug of a cable to a connector block on the Main Board, and a two-wire pigtail for the speaker.

B. The Sensor Board Sub-Assembly is attached by a long screw and a threaded tube (as used for table lamps) to the Base Frame. It contains the gas sensor, the temperature sensor and the transmiter, all of which need to be outside the enclosure.

C: The Display sub-assembly is connected to the base frame by three screws. It has many jumper wires from the display to the processor on the Main Board.

D: The Main Board connects to the Display sub-assembly by two screws.
The processor, a Pro-Mini Arduino, plugs into it.
It has three other atachments: the Real-Time Clock (RTC), the Alarm Board, and the push-button board.

Block Diagram


These are the photos of the finished clock.

Here is the Arduino sketch.

Here are the circuit diagrams.