Day Fourteen.
The last day of the training camp.
Two p.m.
The sunlight outside was a blinding white, and the cicadas’ chirping from the trees was loud enough to be jarring.
Inside the lab, the air conditioner was on full blast, its cold air whooshing out.
Professor Wang wasn’t sitting in his usual corner.
He stood at the front of the room.
On the desk was a messy cardboard box with no blueprints in sight.
Inside were clockwork springs, brass gears from an old clock, a photogate, capacitors of various sizes, crude relays, and a few splintered wooden strips.
"The final problem."
Professor Wang looked at the six youths, who had shed their immaturity, their gazes now steady and composed.
"No test paper, no hints."
"Use the junk in this box."
"Build me a linked mechanical and electrical alarm device, one that can be precisely controlled for a three-minute delay."
"You are not allowed to use any off-the-shelf digital chips. Only pure mechanical and analog circuits."
Professor Wang raised his wrist and glanced at his old Titoni watch.
"Three hours. Begin now."
He didn’t return to his seat, instead remaining at the front of the room to watch them.
The six of them.
Gathered around the messy cardboard box.
Lin Yi was the first to step forward.
She didn’t pick up a pen. She just reached into the box of junk and rummaged around, her brow furrowed slightly.
’A water-drip funnel? Not precise enough.’
’A pure RC circuit for charging and discharging? The leakage current is too high, and it’s unstable due to temperature changes.’
She tossed both items back into the box. Finally, she reached to the very bottom and pulled out a brass pendulum with a gear, then picked out a massive electrolytic capacitor from a component case.
Lin Yi slapped both items onto the center of the table with a CLAP.
"A pure clockwork spring is too inconsistent; it gets slower and slower."
"The capacitor is too leaky; the discharge is uncontrollable."
Lin Yi dusted off her hands and, relying on her intuition, laid out the core physical contradiction of the system.
"The only way is to have them keep each other in check."
"One provides the rhythm, the other stores the energy. That’s the general direction."
With that, Lin Yi took a step back and leaned against the lab bench behind her.
"My intuition only tells me this much. I can’t calculate the specifics of how to put them together."
As soon as she finished speaking,
Chen Zhuo’s hand was already reaching out.
He took the brass pendulum and the capacitor, his mind instantly visualizing Lin Yi’s flash of inspiration.
"Electromechanical coupling."
Chen Zhuo pulled over a blank sheet of scratch paper and uncapped his gel pen.
"Use the mechanical pendulum to interrupt the photogate, creating a high-frequency pulse."
"Use the capacitor to receive the pulses, performing a stepwise integration."
"Lin Yi, good intuition. I’ll take it from here."
Chen Zhuo’s voice was flat, showing little emotion.
The tip of his pen flew across the paper, and an exceptionally clear system topology diagram took shape within ten seconds.
Immediately after, he issued precise and rigorous commands.
"Pendulum length fixed at 24.8 centimeters for a period of approximately one second."
"We need it to block the photogate 180 times. Each blockage will charge for 0.1 seconds."
"Use the 1000μF capacitor."
He looked up.
"Zhou Kai, calculate the amplitude decay equation for the pendulum under air damping. I need to add a dynamic compensation coefficient to the charging circuit."
"Got it."
Zhou Kai pulled out his fountain pen and immediately bent his head over the complex integral calculus.
"Miao Shian, solder the receiver part. Keep the pins as short as possible to reduce parasitic capacitance."
"Roger."
Chen Zhuo’s gaze turned to the remaining two, his eyes revealing seasoned, practical experience.
"Wang Huashao, build the pendulum stand with the wooden strips. Make it perfectly vertical, without the slightest wobble. After assembly, put two drops of oil where the gears mesh to minimize friction."
"No problem."
"He Gui, connect the multimeter to the main capacitor and report the voltage at all times. Your wiring must run flat against the board, far from the high-frequency oscillation area. Reduce spatial interference to zero."
"Understood."
The commands were issued with clarity.
The lab instantly shifted into a high-pressure assembly mode.
Wang Huashao, holding a saw and glue, deftly assembled the wooden stand.
Miao Shian wore an anti-static wrist strap, the tip of his soldering iron precisely spot-welding the components.
Zhou Kai wrote the last line of the compensation formula on the paper and handed it to Chen Zhuo.
During this frantic race against time,
Lin Yi didn’t pace around like a foreman.
She leaned relaxedly against the lab bench, arms crossed, quietly watching Chen Zhuo.
She watched Chen Zhuo take the formula from Zhou Kai.
She watched him connect a tiny variable resistor in series next to the capacitor.
Then, Chen Zhuo picked up a long, flat-head screwdriver. His gaze was so focused it was devoid of any stray thoughts. With a perfectly steady hand, he gently turned the trimming resistor half a rotation, then locked it tight.
A strange light flashed in the depths of Lin Yi’s eyes.
She knew perfectly well.
’My intuition only gave him a single brick, yet this guy somehow instantly built an entire fortress in his mind, complete with error compensation.’
Two hours and forty-five minutes.
An ugly device, with no outer casing and countless wires exposed like blood vessels, sat silently in the center of the lab bench.
On the left was a brass pendulum held up by a wooden stand.
On the right was a perfboard, densely packed with soldered components and connected to a small red light bulb.
Professor Wang held an old mechanical stopwatch in his hand.
He walked up to the table.
"Finished?" Professor Wang asked, looking at them.
"Finished," Chen Zhuo replied calmly.
"Power on. Get ready."
Professor Wang raised the stopwatch. Chen Zhuo’s hand was on the power switch.
Wang Huashao pinched the pendulum’s brass bob, pulling it back to a precise angle.
"Release."
CLICK.
The switch was pressed.
The pendulum was released.
TICK.
The sound of the stopwatch starting rang out at the same time.
The brass pendulum, driven by gravity, swung smoothly through its lowest point.
It cut through the photogate’s weak beam of light.
On the perfboard,
A tiny electrical pulse was sent into the large 1000μF capacitor.
The only sounds in the entire lab were the rhythmic SWISH of the pendulum cutting through the air and the slow but steady climb of the voltage reading on the multimeter in He Gui’s hand.
One minute.
Two minutes.
Due to air resistance, the pendulum’s amplitude began to show a minute, visible decay.
Cold sweat beaded on Zhou Kai’s forehead.
But Chen Zhuo’s precisely-tuned compensation resistor worked perfectly; the minute change in pulse width offset the delay in the count.
The voltage continued to climb at an undiminished rate.
Two minutes, fifty seconds.
The voltage reading approached the breakdown threshold of the Zener diode.
Zhou Kai, Wang Huashao, and Miao Shian’s breathing grew shallow without them realizing it; they even held their breath.
Two minutes, fifty-five seconds.
Two minutes, fifty-eight seconds.
Two minutes, fifty-nine seconds.
The brass pendulum swung through the photogate one more time.
Chen Zhuo stood before the table.
There was no prayer in his eyes, only the absolute confidence that once the design was set, the laws of physics would not deceive him.
He counted down silently in his head.
’Three.’
’Two.’
’One.’
SNAP.
A crisp sound as the relay engaged.
On the perfboard,
The ordinary small red light bulb lit up instantly.
It emitted a piercing red glow.
CLICK.
Professor Wang’s thumb pressed the stop button on the mechanical stopwatch.
He looked down,
gazing at the needle on the stopwatch’s face.
Zhou Kai leaned in for a look.
His pupils contracted sharply.
Three minutes.
Or rather, three minutes and five-hundredths of a second.
This group of middle school students,
using a pile of simple scrap,
had managed to create an electromechanical timer with an error of less than 0.1 seconds.
The last rays of the setting sun,
shone through the lab’s somewhat grimy windows, falling on the crude, red-lit device.
They also fell on the six sweat-drenched faces.
The indicator light’s red glow
shone steadily in the slightly dimming lab.
Not flickering.
Not going out.
It was as if an incredibly long and torturous dream had finally borne its most solid fruit.

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