a Compact, cheap gas sensor with RS-485 connectivity
24V supplied, Gas detector with half-duplex RS-485 interface. For industrial or home use and application ready product, containing a current or voltage output for reference measurment. a sinlge LED used for showing cominucation or Error state. The small footprint makes it ready for most plastic enclosures. the PCB can be hand-solderd with a bit of skill. Use cases can be in Garage systems (linked with the vents and gas alarm system), hobbyist workshop or any other room such as Office spaces and schools.
A STM32G031K8 is the logical unit. Is is cheap and readily available. The very most components use standart fooprints. Thus, they are easily exchangeble in case of a shortage. All parts are SMD, except for the Sensors, DCDC converter and Connectors. All PCB components can be sourced by Mouser, except for the Gas Sensor. For developement purposes (TAG v0.1) a gas sensor type MQ-X were used (MQ-7 and MQ-135) TAG v0.2 makes use of the nemoto sensor, that uses low current and is more gas specific. The I2C conection gives a possibility, to further extend with more sensors, such as the Sensirion SHT4X.
Hardware is developed in KiCad 7.0.
everything is programmed on STM Cube IDE. The Sensor and trim potentiometers are read-in using DMA. The max and minimum values of the potentiometers can be set by the Modbus. the specific address are found in the excel-table "Modbus-memorymap" in the software folder.
Low pass filter for the PWM (from uC to OpAmp to voltag eand current output) has been simulated using LTSpice.
- PWM filter simulations
- build and test prototype
- Prgram IC for analog measurment and analog output
- Find better sensor supplier and include it on second version PCB -> nemoto sensors
- implement Modbus via RS-485
- create Bill of material
- Make second physical prototype