Chapter 17 — Wind Village Robot Team

"TCS3200 color sensor costs one hundred and twenty thousand, but you have to order online, it takes a week to ship here." Gia Han read information from a website selling electronic components, sounding disappointed. "I still have eighteen days. Once the order arrives, half of my training time will be over."

The whole team sat around a wooden table in the warehouse, three small wooden blocks painted red, blue, yellow - painted by Uyen Nhi herself from scraps of wood obtained from a carpentry workshop near the market - placed in the middle of the table like an unsolved puzzle. Without a specialized color sensor, how can the robot distinguish these three blocks using the recycled components on hand?

"Or should I mark it with shapes instead of colors?" Phong proposed. "The red block cuts one hole, the blue block cuts two holes, the robot uses ultrasonic sensors to detect different shapes."

"No, the law clearly states that the block must maintain its standard shape, the surface cannot be modified." Gia Han shook her head and pointed to a paragraph in the regulations. "The organizers must have expected teams to cheat like that."

The group was silent, thinking. Khanh Dan tried to hold back from giving an answer right away, even though she already had a solution in her mind from what she had read about in a research project at NovaTech - but she wanted to see if the team could find a way forward on their own, because she knew that a self-found solution is always more ingrained in the memory than a given solution.

"We have some red, green, and blue LED lights from the broken Christmas lights the other day, right?" Uyen Nhi suddenly spoke up, her eyes still staring intently at the three wooden blocks on the table.

"Yes, why do you ask?" Nam replied, rummaging through the parts box to find a small intact LED light strip.

"I remember when I was studying Fine Arts, the teacher taught about color and said that when red light is shined on it, it reflects brightly, but when blue light shines on it, it looks dark." Uyen Nhi spoke, her voice gradually becoming more confident when she saw the whole team starting to listen attentively. "So if I shine three different colors of light on a wooden block one after another, then measure when that block reflects the brightest, can I guess its color?"

Khanh Dan laughed, unable to hide her surprise mixed with pride. "Uyen Nhi, you just re-invented the exact same principle that people use in industrial color sensors. That's exactly how a TCS3200 chip works inside - it uses a white LED to shine through a color filter, measuring the intensity of reflected light."

"So can I really do it?" Uyen Nhi asked, her eyes shining.

"It can be done. I need a light sensor to measure the intensity of reflection — a photoresistor, a type of device that changes resistance according to the intensity of light shining on it. This is cheap and easy to find." Khanh Dan explained, quickly drawing a diagram on paper. "Attach three red, green, and blue LEDs around a photoresist. Each time I measure, I turn on each light in turn, read the photoresist value, and compare those three values to deduce the color of the wood block."

"Do I have a photoresistor?" Gia Han asked.

"Yes, two were removed from the yard sensor light that broke last year." Phong responded immediately, remembering the exact location in the parts sorting box.

The whole team started working that evening, not waiting until the next day. Phong used a short cut piece of PVC pipe as an outer light cover to prevent environmental light from entering and disturbing the measurement. He attached three colored LED lights around the mouth of the pipe at an even thirty-degree angle as outlined in Uyen Nhi's drawing. Gia Han wrote the control command: turn on the red light, wait five milliseconds for stability, read the photoresistor value, turn off the red light; Repeat the same with green and blue lights; Compare the three readings, and the lowest value — meaning the photoresist receives the most light reflected through that color — will be the color of the block of wood.

On the first try, the red wooden block was inserted into the sensor tube. The laptop screen temporarily connected to view the log displays three numbers: the red light shows the lowest value, as expected.

"Correct red!" Gia Han shouted, continued tapping with the green block, then the yellow block. All three times gave correct results.

"Wait, how can a block of gold be distinguished, because gold is a mixture of red and green?" Nam asked, frowning trying to understand the logic.

"Yes, that's the hardest part." Khanh Dan nodded, satisfied that his question touched the essence of the problem. "The yellow block will reflect strongly both red and green lights, only darkening when shining blue lights. I programmed it so that if both red and green values are almost equally low, while blue is completely high, then the conclusion is that it is yellow."

Gia Han adjusted the command according to that logic and tried again. The block of yellow wood is inserted into the sensor tube, and after a second of processing, the screen displays the text: "Detected color: YELLOW."

The whole warehouse burst into cheers, for the first time after many tense evenings, the atmosphere became completely relieved. Nam lifted the homemade sensor tube high like he was holding up a trophy, Phong patted Uyen Nhi's shoulder repeatedly, and Gia Han hugged her laptop as if that device had just helped her pass a difficult exam.

"I just made a color sensor using broken Christmas lights, hand-cut plastic tubes, and a photoresist removed from an old sensor light." Khanh Dan said, her voice unable to hide her pride. "I think, this is worth much more than a pre-purchased chip of one hundred and twenty thousand."

"Why?" Uyen Nhi asked, even though she seemed to have guessed the answer.

"Because if we buy it ready-made, we just need to know how to plug the wire into the correct pin, we don't need to understand why it works." Khanh Dan replied. "But this one, each person on the team clearly understands why it works, from my idea, to Phong's mechanics, to Gia Han's command. If it has any problems on exam day, we know exactly where to fix it, not blindly guessing like when using pre-purchased items."

Nam placed the sensor tube on the table gently, as if placing a treasure, looking at it with a respect that was different from his usual careless attitude. "So does this have a name yet?"

"Not yet." Khanh Dan shook his head and smiled. "But I think Uyen Nhi deserves to be the one to name it, because the original idea was yours."

Uyen Nhi blushed, looked at the sensor for a moment, then blurted out a name, her voice completely confident, without any trepidation from the afternoon she met Uncle Hung a few days ago. "Wind Eyes." she said. "Because it sees colors through light, just like my eyes see things through sunlight, and my team is the Mountain Wind."

The whole group nodded in agreement, no one objected, and from that moment, "Wind Eyes" officially became the name of the most important part that helps their robot see the world with exactly what they have in hand.

***

While Gia Han and Uyen Nhi continue to refine the command to make "Mat Gio" operate more stably, Nam and Phong focus their efforts on the most unfinished part of the whole robot: the picking arm. The first version, made from two aluminum bars taken from an old TV frame connected to the hinge by screws, was able to pick up the wooden block, but the gripping force was uneven - sometimes the handle was loose and dropped the block midway, sometimes it was too tight, causing the servo motor to vibrate due to overload, emitting an unpleasant hissing sound.

"There has to be a way to know when the grip is tight enough without having to guess." Nam said, rubbing his temples after the fifth consecutive evening of unsatisfactory editing.

"I use the servo motor itself to sense the force." Phong suggested, his eyes lighting up with a flash of an idea. "If the servo has to use more electricity to stay in position, it means it is encountering greater resistance, meaning it has already clamped onto the object. I measure the current through the servo, and when I see a sudden increase in current, I immediately stop closing the gripper, without needing to close it all the way."

Gia Han, even though she was busy with "Wind Eyes", still heard the story and turned to give comments. "That's called electric current feedback control. I read it in the document the other day but didn't understand how to do it. If you can do it, I'll write an additional command to read that value and incorporate it into the main program."

The two started experimenting, using a small resistor in series with the servo power circuit to measure voltage drop — a simple but effective trick for estimating current draw without the need for expensive, specialized current sensors. After a few times of adjusting the threshold, the gripper arm began to close tightly enough to firmly hold the block of wood without causing the motor to overload, a small improvement that made both Nam and Phong look at each other and nod with satisfaction, like two workers who had just completed the most difficult thing to make in their lives.

When it was completely dark, all five of the robot's most important parts — the rubber-coated four-wheeled chassis, the motor control circuit, the ultrasonic obstacle-avoiding sensor, the force-feedback gripper arm, and the color-detecting "Wind Eye" — were assembled into a complete block for the first time, placed in the middle of the table like a strange mechanical creature assembled from countless different pieces of life: a broken piece of television, a Christmas light no one remembers when it was purchased, a servo box. toys were left in the corner of the yard, a coil of copper wire had been in a burned fan. No one on the team said it out loud, but when they looked at the robot under the pale yellow oil lamp light, they all felt the same thing: this was no longer an experimental project, but a living body assembled from the stories of each person on the team.