Episode Summary: GPS Has a Secret Job

Summary

In "GPS Has a Secret Job," Sean Hodgins welcomes Jeff Geerling to his workshop for a hands-on electronics building session centered around a custom GPS PPS Watch project. The episode opens with Sean's philosophical musings on time — "It's the one thing I can't make. But maybe I can get some of it back" — setting up the central theme of precision timekeeping using GPS technology. The show is framed through a humorous "Cooking Circuits with Shawn" format complete with fake studio audience reactions, though Jeff appears skeptical of the theatrical presentation.

Sean reveals he created this watch project specifically for Jeff's visit in typical last-minute fashion, with only 2 weeks to design, order boards, and prepare. The project is a wristwatch that doesn't tell traditional time but instead uses GPS satellites' Pulse Per Second (PPS) signals for extremely accurate timing. As Sean explains, "Most people think GPS is for maps and it is, but the way GPS works is by measuring time very accurately." The watch features LEDs that blink with GPS timing pulses and includes BNC connectors to compare timing accuracy between different GPS sources.

The episode showcases Jeff's first experience soldering a complete surface mount circuit board using solder paste and stenciling techniques, with sponsorship from PCBWay. The duo encounters challenges including expired solder paste and the difficulty of soldering large metal connectors. After successful assembly and testing, both watches demonstrate perfect synchronization, revealing the deeper meaning behind the project: that two people wearing these watches anywhere on the planet will see their LEDs blink together as long as both have clear views of GPS satellites — it's time itself that connects them, not proximity.

Conversation

Opening Philosophy and Project Introduction

The episode opens with Sean's reflections on time, where he muses: "Some people like to embrace time. Others are scared of it. I find myself somewhere in the middle. We also tend to waste it. And yet, we're always trying to get more of it. It's the one thing I can't make. But maybe I can get some of it back." This philosophical opening establishes the thematic foundation for the entire episode.

Sean introduces the "Cooking Circuits with Shawn" format with theatrical flair, including fake studio audience reactions. Jeff Geerling appears skeptical of the presentation, questioning whether there's actually an audience and who Sean is talking to. Sean admits to creating this GPS PPS Watch project specifically for Jeff's visit: "Typical Sean Hodgins fashion, uh Jeff is coming in 2 weeks, and I suddenly have the urge to make a project last minute."

GPS Technology Explained

Sean provides an accessible explanation of how GPS technology fundamentally works through precise timing rather than just positioning. The watch doesn't tell time in the traditional sense but uses GPS satellites' Pulse Per Second (PPS) signals — "one electrical pulse every second" — for extremely accurate timing. The project features LEDs that blink with GPS timing pulses, with BNC connectors enabling comparison between different GPS sources. A third LED only lights up when two timing signals are out of sync, providing a visual indicator of synchronization accuracy.

Surface Mount Soldering Tutorial Begins

The hands-on portion begins with Jeff's first complete surface mount circuit board assembly. Sean guides him through the process of aligning the PCB in a specialized jig and applying 5-year-old expired solder paste with a squeegee. The aged paste will need oven reflow since it no longer melts normally. Jeff's first squeegee attempt creates uneven results that Sean humorously compares to making a fish shape.

Sean introduces his workshop tools, including equipment from PCBWay (the sponsor who manufactured the boards), components from Digi-Key, and a vacuum pump from Robbins. He emphasizes making electronics accessible, noting he originally considered having Jeff use a pick-and-place machine but decided manual placement would be more fun, calling it "the modern pick and place."

Component Placement and KiCad Integration

Sean demonstrates KiCad's interactive BOM feature, which generates an HTML guide showing component locations, quantities, and pin orientation — a feature that integrates directly with Digi-Key for ordering. Jeff learns vacuum pickup tool operation, initially struggling with foot pedal coordination: "I have to get my foot communicating with my brain there." He successfully places small discrete components like 0.1 microfarad capacitors, though he accidentally puts red LEDs on the outside instead of green, opposite to Sean's pre-built version.

Reflow Process and Sponsorship

After Jeff completes component placement, Sean loads the board into his Control IO 3 reflow oven, an upgrade from his previous $20 toaster oven method where he manually watched and timed the process. During the reflow cycle, Sean delivers a PCBWay sponsorship message explaining how their manufacturing services "save me the one thing that I can't make, and that's time." He offers viewers the code "shawn.hodgins10" for $10 off orders of $30 or more (first 100 uses).

Hand-Soldering Challenges

Jeff faces his biggest challenge: hand-soldering the large metal BNC connectors. Sean warns him: "because this whole connector is metal, you pretty much have to heat up this whole bottom part before it'll start flowing solder. It's a huge pain." Despite exclaiming "Holy cow. Come on, man," Jeff succeeds and completes his first board, joking: "Yeah, first time complete from scratch. Don't look at the solder too closely."

Sean reveals a pre-built watch in classic cooking-show fashion: "And because this is a cooking show, we already have one pre-built, 3D printed." He notes the LED color reversal will help differentiate the two units.

GPS Signal Acquisition and Testing

The testing phase begins as both watches need GPS satellite acquisition through window placement. The process proves initially challenging as they struggle to get both watches to acquire GPS signals simultaneously due to indoor interference. Jeff tries various positions, including holding his watch up for better satellite reception, while Sean explains that the middle LED will only blink when the timing signals are out of sync.

After moving closer to a window for better GPS signal reception, both watches successfully achieve GPS lock and demonstrate perfect synchronization. Sean notes: "technically to us they are perfectly in sync" — to the human eye, there is no green LED visible, meaning the watches are blinking in perfect sync.

The Deeper Meaning Revealed

Sean delivers the episode's key revelation about the profound implications of synchronized timing: "And the weirdly cool part is that if two people are wearing one of these and they both have a clear view of the sky, the watches should blink in sync. They don't need to be near each other. One person could be here and the other could be on the other side of the planet. As long as both watches can see GPS satellites, they're both listening to the same clock system. So, the LEDs blink together. It's time that connects them."

Closing and Open Sauce Invitation

Sean encourages viewers to build their own GPS watches using the open-source files and bring them to Open Sauce, where they can synchronize with his. The episode concludes with a brief gift exchange where Sean gives Jeff a "more token" he had never given him before. Sean closes with his philosophical statement: "I live my life one extremely accurate second at a time. Nothing else matters. With that perfectly synced one second pulse, I'm free."

Highlights

Opening philosophy on time — Sean sets the thematic tone: "It's the one thing I can't make. But maybe I can get some of it back."
GPS isn't just for maps — Sean explains the fundamental principle: "Most people think GPS is for maps and it is, but the way GPS works is by measuring time very accurately."
Jeff's foot-pedal coordination struggles — While learning the vacuum pickup tool: "I have to get my foot communicating with my brain there."
The BNC connector soldering challenge — Sean warns about the difficulty: "because this whole connector is metal, you pretty much have to heat up this whole bottom part before it'll start flowing solder. It's a huge pain." Jeff perseveres despite exclaiming "Holy cow. Come on, man."
Jeff completes his first surface mount board — With characteristic modesty: "Yeah, first time complete from scratch. Don't look at the solder too closely."
Perfect synchronization achieved — Both watches blink in perfect sync after GPS acquisition, with Sean noting "technically to us they are perfectly in sync."
The poetic revelation — Sean explains the deeper meaning: "And the weirdly cool part is that if two people are wearing one of these and they both have a clear view of the sky, the watches should blink in sync. They don't need to be near each other. One person could be here and the other could be on the other side of the planet... It's time that connects them."
Closing philosophical statement — Sean concludes with: "I live my life one extremely accurate second at a time. Nothing else matters. With that perfectly synced one second pulse, I'm free."