Hi all,

I'm starting a new safety project and need some help planning the circuit design.
The main goal is to create a hydrogen safety alarm system. We have a custom in-house development board called a "Bus Interface" that the circuit will be based on. This Bus Interface board provides us with various power voltages, some GPIOs to work with, and a pre-existing CAN connection.

Here are the specific requirements for the circuit I need to design:

- Sensor Interface: The circuit must connect to a cabled hydrogen gas sensor. Specifically, we are using one of the DFRobot Gravity sensors (details here: Link). The sensor communicates using a digital protocol (I2C or UART), so the circuit needs to be able to read this digital data.

- Status Indication: We need a simple visual indicator (like a standard LED) that shows the sensor is connected, powered, and communicating correctly. This is just to confirm the system is "alive."

- CAN BUS Communication: The sensor information (the hydrogen concentration) needs to be communicated over our CAN BUS.Note: A key point is that we do not need to design CAN Hardware; CAN is provided by the Bus Interface! Our circuit just needs to process the sensor data and pass the information to the Bus Interface's CAN port.

-High-Current Alarm: This is the critical safety feature. If the hydrogen concentration exceeds a specific threshold (1000 ppm), a very bright visual alarm must be triggered. This LED needs to be high-intensity, requiring more than 30 mA of current.

- PCB Constraint: The final design must fit on a two-layer PCB.

I'm trying to figure out the best way to design the schematic that ties all of this together. I need to handle the digital sensor, manage the two different visual feedback LED (the low-power status light and the high-current alarm), and correctly pass the data to the CAN logic on our Bus Interface.
I'm not sure where to start with designing the schematic for the alarm driver and the sensor interfacing (I'm beginner). Does anyone have suggestions for a circuit diagram or block diagram that could accomplish this?

 

I'm not sure where to start with designing the schematic for the alarm driver

For starters the module has a programmable alarm output (ALA) that can power the LED through a driver circuit.
Another option is using the analog output (VO) to activate an Alarm function and "In Use" function.

 

THis sounds very much like the sort of project I would do at one place of employment quite a few years ago. This is a good project for a good applications engineer, electrical/electronic. From the description of the existing universal interface PCB, the harder part is done.

Commercial rates applied then. Commercial rates would still apply.

 

Where would high concentrations of hydrogen occur, that you have to monitor?

 

Another option is using the analog output (VO) to activate an Alarm and "In Use" function.
As VO increases or decreases will be indicated by LEDs 2 -10 in the form of a bar graph.
LED10 indicates and alarm condition and activates high current LED1.

 

Since the sensor board has to be connected via UART/I2C you need a small microcontroller with integrated UART or I2C plus CAN to connect to your bus interface. The STM32 Familiy for example has a lot of parts that will fit your needs.

You can connect your signalling LED to an output port of the controller via a BJT or FET.

 

Thanks for the schematic!
Does this design also ensure that the sensor is actually connected and working, or does it only react to the VO signal?
And if I want to reduce the display to just five stages instead of ten, how should I modify the LM3914 connections?

 

Does this design also ensure that the sensor is actually connected and working, or does it only react to the VO signal?
And if I want to reduce the display to just five stages instead of ten, how should I modify the LM3914 connections?

Reacting to the VO signal does indicate the sensor is working.
From the spec sheet for the SEN0473 H2 sensor and my calculations the VO ranges from 0.6V at 0ppm to 2.0V at 1000ppm.
Edited version:
LED1 = appx 0ppm to 142ppm
LED2 = appx 143ppm to 427ppm
LED3 = appx 428ppm to 713ppm
LED4 = appx 714ppm to 999ppm
LED5 = appx 1000ppm or higher

 

Hi all,

I'm starting a new safety project and need some help planning the circuit design.
The main goal is to create a hydrogen safety alarm system. We have a custom in-house development board called a "Bus Interface" that the circuit will be based on. This Bus Interface board provides us with various power voltages, some GPIOs to work with, and a pre-existing CAN connection.

Here are the specific requirements for the circuit I need to design:

- Sensor Interface: The circuit must connect to a cabled hydrogen gas sensor. Specifically, we are using one of the DFRobot Gravity sensors (details here: Link). The sensor communicates using a digital protocol (I2C or UART), so the circuit needs to be able to read this digital data.

- Status Indication: We need a simple visual indicator (like a standard LED) that shows the sensor is connected, powered, and communicating correctly. This is just to confirm the system is "alive."

- CAN BUS Communication: The sensor information (the hydrogen concentration) needs to be communicated over our CAN BUS.Note: A key point is that we do not need to design CAN Hardware; CAN is provided by the Bus Interface! Our circuit just needs to process the sensor data and pass the information to the Bus Interface's CAN port.

-High-Current Alarm: This is the critical safety feature. If the hydrogen concentration exceeds a specific threshold (1000 ppm), a very bright visual alarm must be triggered. This LED needs to be high-intensity, requiring more than 30 mA of current.

- PCB Constraint: The final design must fit on a two-layer PCB.

I'm trying to figure out the best way to design the schematic that ties all of this together. I need to handle the digital sensor, manage the two different visual feedback LED (the low-power status light and the high-current alarm), and correctly pass the data to the CAN logic on our Bus Interface.
I'm not sure where to start with designing the schematic for the alarm driver and the sensor interfacing (I'm beginner). Does anyone have suggestions for a circuit diagram or block diagram that could accomplish this?

Start by dividing your circuit into four blocks: the hydrogen sensor interface, MCU, LED indicators, and CAN interface. Connect the DFRobot Gravity sensor to the MCU using I2C or UART, adding pull-up resistors if using I2C. Power the sensor from the Bus Interface’s regulated voltage. Use a GPIO to drive a low-current status LED through a series resistor to indicate the sensor is powered and communicating.


For the high-current alarm LED, use a logic-level N-MOSFET or NPN transistor driven by another MCU GPIO. Place a current-limiting resistor in series with the LED and ensure traces can handle >30 mA. The MCU reads sensor data and sends hydrogen concentration to the Bus Interface for CAN communication. Keep the PCB layout compact, with sensor, LEDs, and transistor close to the MCU, and use wide traces for high-current paths.