These show views of the Gas Sensor

This is the front view with the cover on. To push the buttons, the cover must be lifted off.
Removing three screws at the bottom allow the Display sub-assembly and attached Main Board to be removed.
This allows access to the Main Board with removal only of the three power, two speaker wires, and the ribbon plug.

Front view

This is the back view with the cover on.
It shows the Sensor sub-assembly with its cover installed. The wire is the antenna.

Back View

This is the top view with the cover off, showing mainly the Main Board and the speaker. The sensor Board cover is installed but you can see the top of the sensor. The thermometer sticks out to keep it away from the hot sensor.
The assembly seen edge-on is the Alarm Board, which attaches to the Main Board with a single screw. It connects with five jumper wires.
Above the Alarm Board is the audio amplifier.
To the right of the Alarm Board is the plug-in RTC. which uses I2C. Hopefully its tiny, soldered-in, battery will last forever.
Next is the light sensor, its circuit, the 1.5V regulator I2C and the sensor heater relay.
Last is the plug-in Arduino processor and a whole mess of jumper wires.

Top virw

This is the wiring side of the Sensor Board. I am not proud of it!


There is another board behind what you can see of the Alarm Board. This contains sockets, interconnections, and some parts. The rgb alarm LED is also connected to it.

The top board is an audio decoder for files with the ogg extension, for which it has internal storage.
It selects a file with a name corresponding to the numbered pins on the top, and makes a sound signal for the audio amplifier when pulsed.

The lower board is an I2C 8-bit port expander wired to directly match the connector of many common LCD displays. In this application three outputs drive the LED and the other five go to the audio board.

The audio amplifier is in front of the Alarm Board

The RTC, the Light Sensor, its circuit, and the 1.5V regulator are in this photograph, but are difficult to make out.

Alarm Board

This is the the default display.

Gas Display

This is the the alternate display, the push-buttons, and their encoding resistor pack. It is wired to the Main Board.

Gas Display