This week, I finally figured out a simple way to build the device for sensing the pingpong table! Although I haven’t collected data for the entire week, I still updated the dashboard based on the existing data. Let’s talk about the creation process.

Objectives

Generally speaking, I want to analyze the usage patterns of the pingpong table on the floor and answer questions like:

• How often do students use the table?
• Which game lasts the longest?
• What is the most popular day for using the table?

So, I don’t need highly accurate data to answer these questions. I also want the technology used in this project to be as simple as possible. I’ve tried the following methods:

• Sensing the vibration of the table with the SW-520D sensor. Too small to detect.
• Sensing the sound of the pingpong ball hitting the table. Requires extra sound processing.

Is there a simpler but effective method besides these two? Based on my experience, I made an observation:

No matter how good or bad you are, there’s always a chance you’ll touch the net when playing pingpong.

From that, the solution emerged: sense the vibration of the net!

Building the Device

I ended up using the SW-520D sensor to detect the vibration of the net.

I modified Tom’s Arduino MQTT code slightly to send the data to the broker:

int sensorReading = digitalRead(VIBRATION_SENSOR_PIN);
if (sensorReading != LOW) return;
if (mqttClient.connected()) {
  // ....
  Serial.print("published a message: ");
  Serial.println(sensorReading); // Send zero!!!
}

I didn’t do much fabrication work because, again, I want this project to be as simple as possible. Plus, people are more likely to engage with things that look fragile! Below is how I connected it to the net.

Testing