Light Transport And Constructing Images From A Projector’s Point Of View

Imagine you have a projector pointing at a scene, which you’re photographing with a camera aimed from a different point. Using the techniques of modelling light transport, [okooptics] has shown us how you can capture an image from the projector’s point of view, instead of the camera—and even synthetically light the scene however you might like.

The test scene used for the explanation of the work.

The concept involves capturing data regarding how light is transported from the projector to the scene. This could be achieved by lighting one pixel of the projector at a time while capturing an image with the camera. However, even for a low-resolution projector, of say 256×256 pixels, this would require capturing 65536 individual images, and take a very long time. Instead, [okooptics] explains how the same task can be achieved by using binary coded images with the projector, which allow the same data to be captured using just seventeen exposures.

Once armed with this light transport data, it’s possible to do wild tricks. You can synthetically light the scene, as if the projector were displaying any novel lighting pattern of your choice. You can also construct a simulated photo taken from the projector’s perspective, and even do some rudimentary depth reconstruction. [okooptics] explains this tricky subject well, using visual demonstrations to indicate how it all works.

The work was inspired by the “Dual Photography” paper published at SIGGRAPH some time ago, a conference that continues to produce outrageously interesting work to this day.

Continue reading “Light Transport And Constructing Images From A Projector’s Point Of View”

2025 One Hertz Challenge: The Easy Way To Make A Nixie Tube Clock

Let’s say you want to build a Nixie clock. You could go out and find some tubes, source a good power supply design, start whipping up a PCB, and working on a custom enclosure. Or, you could skip all that, and just follow [Simon]’s example instead.

The trick to building a Nixie clock fast is quite simple — just get yourself a frequency counter that uses Nixie tubes for the display. [Simon] sourced a great example from American Machine and Foundry, also known as AMF, the company most commonly associated with America’s love of bowling.

The frequency counter does one thing, it counts the number of pulses in a second. Thus, if you squirt the right number of pulses to represent the time — say, 173118 pulses to represent 5:31 PM and 18 seconds — the frequency counter effectively becomes a clock. To achieve this, [Simon] just hooked an ESP32 up to the frequency counter and programmed it to get the current time from an NTP time server. It then spits out a certain number of pulses every second corresponding to the current time. The frequency counter displays the count… and there you have your Nixie clock!

It’s quick, dirty, and effective, and a sweet entry to our 2025 One Hertz Challenge. We’ve had some other great entries, too, like this nifty hexadecimal Unix clock, and even some non-horological projects, too!

Continue reading “2025 One Hertz Challenge: The Easy Way To Make A Nixie Tube Clock”

The 64-Degree Egg, And Other Delicious Variants

Many of us have boiled an egg at some point or another in our lives. The conventional technique is relatively straightforward—get the water boiling, drop the egg in, and leave it for a certain period of time based on the desired consistency. If you want the yolk soft, only leave it in for a few minutes, and if you want it hard, go longer.

Ultimately, though, this is a relatively crude system for controlling the consistency of the final product. If you instead study the makeup of the egg, and understand how it works, you can elicit far greater control over the texture and behavior of your egg with great culinary benefits.

Continue reading “The 64-Degree Egg, And Other Delicious Variants”

A PC That Uses Hot Coffee As Coolant

Modern computers generate a great deal of heat when under load, thus we cool them with fans and sometimes even water cooling systems. [Doug MacDowell] figured that water was alright, but why not use coffee instead?

Someone tell us how [Doug] made this graph look like it’s right out of a 1970s college textbook.
The concept is simple enough — replace water in a PC’s cooling loop with fresh-brewed coffee. [Doug] fully integrated an entire PC build on to the side of a General Electric drip coffee maker. It’s an absolute mess of tubes and wires, but it’s both a PC and a functional coffee maker in one.

The coffee maker percolates coffee as per normal into the carafe, and from there, it’s then pumped through two radiators on top of the PC. From there, it circulates to the water block on top of the CPU, and then back to the carafe on the coffee maker where the cycle repeats. Doug notes the coffee is initially so hot (90 C) that the PC is at risk of crashing, but after 75 minutes circulating through the system, the coffee and CPU sit at an equilibrium temperature of 33 C.

You can’t really drink coffee from this machine. PC water cooling components are not food safe in any way, and [Doug] notes mold will become an issue over time. For short periods at least, though, it’s possible to sort-of-cool your computer with hot, fresh coffee if you really want to do that.

We’ve featured some great hacks of conventional coffee machines over the years, including this fantastic talk at Supercon 2023.

Continue reading “A PC That Uses Hot Coffee As Coolant”

2025 One Hertz Challenge: An Animated Ferrofluid Display

Ferrofluid is fun. You’ve probably seen all kinds of demos with it bouncing around in response to magnetic fields, or dancing near a speaker. [beastie417] decided to turn the entertaining fluid into a display.

The basic concept of the ferrofluid display. Note the header image of this article shows the electromagnet array without the ferrofluid pane in place.

The concept is straightforward enough. First, construct a tank of ferrofluid with a white panel behind it for contrast. Then, place it in front of a grid of electromagnets. Now you have many “pixels” you can turn on and off. You turn a magnet on to attract ferrofluid to that point, and turn it off to let it fall away. Since the ferrofluid contrasts with the white background, you have a viable display!

[beastie417] notes that while the concept is simple, the execution is hard. Ferrofluid can be very difficult to work with, instantly staining many materials like acrylic and even glass that isn’t properly prepared. It can also be quite expensive to construct a display like this, with [beastie417] noting their 16×12 pixel design costing approximately $700 thus far. Then you have to figure out how to drive all the pixels—this project uses DRV8908 coil driver ICs running off a microcontroller which controls the display and handles animations.

We’ve seen some great ferrofluid displays before, like this neat build that could even create readable glyphs. Meanwhile, if you’re doing rad things with the coolest fluid of the new millennium, don’t hesitate to let us know!

A Robot Controller With The Compute Module 5

The regular Raspberry Pi line is a flexible single-board computer, but sometimes you might find yourself wishing for a form factor that was better designed for installation into a greater whole. This is why the Compute Module variants exist. Indeed, leveraging that intention, [Hans Jørgen Grimstad] has used the powerful Compute Module 5 as the heart of his “Overlord” robot controller.

The Compute Module 5 offers a powerful quad-core 64-bit ARM chip running at 2.4 GHz, along with anywhere from 2 to 16GB of RAM. You can also get it with WiFi and Bluetooth built in onboard, and it comes with a wide range of I2C, SPI, UART, and GPIO pins to serve whatever ends you envision for them. It’s a whole lot of capability, but the magic is in what you do with it.

For [Hans], he saw this as a powerful basis for a robot controller. To that end, he built a PCB to accept the Compute Module 5, and outfit it with peripherals suited to robotics use. His carrier board equips it with an MCP2515 CAN controller and a TJA1051 CAN transceiver, ideal for communicating in a timely manner with sensors or motor controllers. It also has a 9-axis BNO055 IMU on board, capable of sensor fusion and 100Hz updates for fine sensing and control. The board is intended to be easy to use with hardware like Xiaomi Cybergear motors and Dynamixels servos. As a bonus, there is power circuitry on board to enable it to run off anything from 5 to 36V. While GPIOs aren’t exposed, [Hans] notes that you can even pair it with a second Pi if you want to use GPIOs or camera ports or do any other processing offboard.

If you’re looking for a place to start for serious robot development, the Overlord board has plenty of capability. We’ve explored the value of the Compute Module 5 before, too. Meanwhile, if you’re cooking up your own carrier boards, don’t hesitate to let the tipsline know!

Australia’s Space Program Finally Gets Off The Pad, But Only Barely

Australia is known for great beaches, top-tier coffee, and a laidback approach to life that really doesn’t square with all the rules and regulations that exist Down Under. What it isn’t known for is being a spacefaring nation.

As it stands, a startup called Gilmour Space has been making great efforts to give Australia the orbital launch capability it’s never had. After numerous hurdles and delays, the company finally got their rocket off the launch pad. Unfortunately, it just didn’t get much farther than that.

Continue reading “Australia’s Space Program Finally Gets Off The Pad, But Only Barely”