So far, the Figaro Journal has introduced methods for acquiring analog data using DC power supply and an evaluation module, acquiring analog data using an evaluation chamber, and acquiring analog data from Gas Sensors and Evaluation Modules during Exposure to Gases.

Analog output allows for the direct acquisition of continuous electrical signals, enabling slight changes to be represented as smooth, continuous values, and conveying the original information with high fidelity.

On the other hand, it also has drawbacks such as being prone to physical limitations and being susceptible to noise.

In contrast, digital output--introduced in this article--represents numerical or encoded values in discrete format that are converted from electrical signals, and has the advantages of making data duplication and transmission easier, as well as offering better compatibility with computer processing.

However, it has limitations in expressing slight changes and requires a microcomputer or dedicated software for transmission and reception.

In this article, we will explain in detail how to acquire gas sensor data using the gas sensor module "FCM2630-J0A," which employs "open collector output," one of the most common digital output formats.

What Is the Difference Between Digital Output and Digital Communication?

In general, digital output refers to a function that expresses two states--on/off (0 or 1)--using electrical signals. In contrast, digital communication refers to the function of transmitting and receiving data via digital signals (0 and 1).

Thus, digital output is used to send electrical signals externally to control devices or transmit information, while digital communication is used specifically for data transmission and reception. Digital communication also employs specific communication standards such as RS232 and RS485.

Let's take a closer look at digital output and digital communication.

◾️Types of Digital Output

There are various types of digital output, including relay output, transistor output (such as open collector output), TTL output, and PWM output.

It is important to select the optimal output format for the characteristics of the equipment used, the intended application, and the operating environment.

◾️Types of Digital Communication

In digital communication, in addition to the difference in transmission methods--such as wired and wireless--there are two main data transmission formats: "serial communication" and "parallel communication."

"Serial communication" refers to "transmission in series," while "parallel communication" refers to "transmission in parallel." Generally, parallel communication is used for data transfer within a device, whereas serial communication is more commonly used for external data exchange, such as communication between devices or signal transmission from sensors.

While parallel communication may seem advantageous in that it can transmit and receive large amounts of data simultaneously, it requires multiple signal lines, which complicates the circuitry and tends to increase costs. Additionally, since data must be precisely synchronized across all signal lines, there are limitations to increasing speed.

For these reasons, "serial communication," which is simpler, easier to handle, and well-suited for long-distance transmission, has become the mainstream approach today.

What Is Open Collector Output?

Open collector output is a type of output method that uses an electronic component called a transistor and is commonly used for controlling external devices. It is called "open collector" because the "collector terminal" of the transistor is used directly as the output terminal.

This method is classified as a "non-contact output," meaning it has no mechanical contacts, which allows for high-speed operation and reliable control.

However, because the transistor's switching action pulls the signal line down to "GND (0V)" for open collector output, an external pull-up resistor is required to pull the output line up to the supply voltage level in order to achieve a logical "High (1)" signal.

◾️Advantages of Open Collector Output

The advantages of open collector output include the ability to wire multiple outputs together using a wired-OR connection, and the relative ease of connecting devices that operate at different voltage levels.

◾️Connecting Pull-Up Resistors and Pin Configuration

In this article, we will take a detailed look at how to acquire data using open collector output, taking the gas sensor module FCM2630-J0A as an example.

Product specifications

As shown in the table above, the product specifications clearly state: "Output signal: NPN open collector (Use in combination with an external pull-up resistor)." Therefore, in order to acquire open collector output, it is necessary to connect an external pull-up resistor.

Pin configuration diagram

Connector type: S05B-PASK-2 (manufactured by JST)

Compatible housing: PAP-05V-S (manufactured by JST)

Specifically, based on the pin configuration diagram of this module, 10kΩ pull-up resistors are externally connected between Pin 3 and Pin 5, and between Pin 4 and Pin 5 respectively  to acquire the output signals.

In the next section, we will explain actual wiring examples and procedures for reading signals based on this configuration.

Acquiring Data from a Gas Sensor Using Open Collector Output

Now, we will explain the equipment required and the procedure for acquiring output data from the gas sensor using open collector output.

◾️Required Equipment

The following items are necessary to acquire data from the gas sensor:

• Digital oscilloscope (2 channels or more)
  ・OWON's SDS1022
  ・Siglent's SDS1052DL+
  ・Tektronix's TBS1052C / TBS2104B
  ・KEYSIGHT's EDUX1052A, etc.

◾️Preparation for Data Acquisition

Now, let's begin preparing for data acquisition.

In this article, to make the data acquisition process easier to understand and as simple as possible, we will explain a method for obtaining signals by directly soldering wires to the lead terminals of the connector located on the back side of the FCM2630-J0A module's PCB.

This approach allows the sensor output to be obtained relatively easily even if you don't have a dedicated connector or jig on hand. To make the process easier even for first-time users, the next section will also cover key points for wiring.

(1) Wiring connections to the gas sensor module

While the FCM2630-J0A comes with a dedicated connector, using it requires special tools and connector parts for crimping the wires. For beginners or those conducting quick prototyping, this may be somewhat cumbersome.

Therefore, in this case, we will explain a configuration that enables signals to be obtained as simply as possible by directly soldering wires to the exposed lead terminals of the connector located on the back side of the module's PCB.

Note that the module's PCB is coated with a protective agent, so be sure to wipe it off using ethanol or a similar solvent before soldering.

(2) External connection of pull-up resistors

① Using a breadboard
To organize the wiring in a visually clear manner, a breadboard is used in this setup. Additionally, a USB Type-C conversion board is employed for conveniently supplying 5VDC power.

② Component placement and wiring on the breadboard
As shown in Figures A to C above, place and connect the following components on the breadboard:

• USB Type-C conversion board
• Two 10kΩ leaded resistors (for pull-up)
• Jumper wires (red, black, yellow, orange)

*For instructions on how to use a breadboard, please refer to the manufacturer's user manual or documentation.

③ Power supply and voltage check
Turn on the USB Type-C power supply connected to the breadboard and measure the output voltage using a multimeter. In this measurement, the voltage displayed was 5.10 V.

*There may be variations among USB power supplies. It is recommended to use one only after confirming that it meets the rated voltage specifications of the sensor module.

④ Connecting jumper wires to the sensor module
With the USB power supply turned OFF, connect the jumper wires on the breadboard (black, red, yellow, orange) to the four lead wires soldered to the sensor module (gray, red, yellow, orange), as shown in Figure D.

*The four lead wires (gray, red, yellow, orange) correspond to Pins 1, 5, 3, and 4 of the module, respectively. (Pin assignments are based on the FCM2630-J0A pin configuration diagram.)

Pin configuration

Connector type: S05B-PASK-2 (manufactured by JST)
Compatible housing: PAP-05V-S (manufactured by JST)

(3) Connecting to a digital oscilloscope

Finally, use a digital oscilloscope to observe the sensor's output signals. In this example, we use Tektronix's TBS1052C.

Prepare two oscilloscope probes for channels CH1 and CH2, and connect them as follows: (Refer to Figures D to F for connection details.)

• CH1 probe → Pin 3 with a pull-up resistor connected
• CH2 probe → Pin 4 with a pull-up resistor connected

This completes all wiring connections.

Finally, turn on the 5VDC power supply and the digital oscilloscope. Then, adjust the oscilloscope settings (voltage range, time base, trigger, etc.) so that the signal waveforms from each of the two channels are displayed correctly.

*For detailed operation instructions, please refer to the user manual of your digital oscilloscope.

How to Interpret the Acquired Data

Figure A shows the waveform monitored in a clean laboratory environment.

• Pin 3 output (Vout2 - Total operating time): H:75msec./L:300msec. (0 to 5 years)
• Pin 4 output (Vout1 - Status mode output): H:75msec./L:300msec. (Monitoring mode)

For both Pin 3 and Pin 4 outputs, it can be observed that Hi/Lo signals are generated with a period of 375 msec, consisting of a high output for 75 msec. and a low output for 300 msec.

This matches the expected behavior described in the FCM2630-J0A datasheet, confirming that the module is in normal (monitoring) mode.

Pin 3 output (Vout2)

Pin 4 output (Vout1)

Priority order of status modes: ①Alarm, ②Malfunction, ③ Initial, ④ Monitoring

Next, the module was placed inside a gas chamber and exposed to a refrigerant gas (R-32) atmosphere. As a result, the output of Pin 3 remained unchanged, while the output of Pin 4 changed as shown in Figure B.

• Pin 3 output (Vout2 - Total operating time): H:75msec./L:300msec. (0-5 years)
• Pin 4 output (Vout1 - Status mode): H:225msec./L:150msec. (Alarm mode)

According to the FCM2630-J0A datasheet, when in alarm mode, Pin 4 outputs a signal of "H: 225 msec./L: 150 msec." This confirms that the sensor correctly entered the Alarm mode upon detecting gas.

By following the above procedure, you can verify that the module is operating normally. Finally, save the data to the digital oscilloscope to complete the procedure.

Analyzing Data Saved on a Digital Oscilloscope

The data saved on the digital oscilloscope can be transferred to a PC using a USB flash drive or similar device. Once transferred, you will find files in formats such as CSV and JPEG, as shown below.

The figures below show examples of how the saved CSV data and JPEG image appear when opened, which were obtained by measuring the output signals from Pin 3 and Pin 4 of the gas sensor module FCM2630-J0A using a digital oscilloscope.

The previously saved CSV data was opened in Microsoft Excel, and graphs were generated for analysis. The results are as follows:

The graphs show the same signal patterns as those captured and saved earlier in the JPEG image from the digital oscilloscope.

• CH1 (Vout2 / Pin 3): High: 75 msec. / Low: 300 msec.
• CH2 (Vout1 / Pin 4): High: 225 msec. / Low: 150 msec.

These results confirm that the output from CH2 (Vout1 / Pin 4) matches the timing specified in the FCM2630-J0A product specifications for "Alarm mode: High 225 ms / Low 150 ms."

Therefore, it can be concluded that this measurement data represents the output from the module after entering alarm mode in response to gas detection.

Conclusion

In this article, we explained how to acquire signals using open collector output, taking the gas sensor module FCM2630-J0A as an example.

By going through the entire process--from wiring on a breadboard and powering the module via a USB power supply, to observing waveforms with a digital oscilloscope and analyzing CSV data--we believe that everyone was able to gain a visual and quantitative understanding of the module's output specifications.

We also covered the basic knowledge of digital output and how to handle open collector outputs, which should serve as a useful foundation for anyone working with sensor applications.

In the next article, we will delve deeper into digital communication, including practical examples.