2025 One Hertz Challenge: Using Industrial Relays To Make A Flasher

August 10, 2025 by Lewin Day 8 Comments

These days, if you want to flash some LEDs, you’d probably grab a microcontroller. Maybe you’d go a little more old-school, and grab a 555. However, [Jacob] is even more hardcore than that, as evidenced by this chunky electromechanical flasher build.

[Jacob] goes into great detail on his ancillary write-up, describing how the simple building blocks used by industrial control engineers can be used to make a flasher circuit that cycles once per second. Basically, two relays are paired with two 0.5-second delay timers. The two relays tag each other on and off on delay as their timers start and expire, with the lamp turned on and off in turn.

We’ve had lots of other great entries to our One Hertz Challenge, too — from clocks to not-clocks. There’s still time to get an entry in — the deadline for submission is Tuesday, August 19 at 9:00AM Pacific time. Good luck out there!

2025 One Hertz Challenge: Blinking An LED The Very Old Fashioned Way

August 5, 2025 by Jenny List 10 Comments

Making an LED blink is usually achieved by interrupting its power supply, This can be achieved through any number of oscillator circuits, or even by means of a mechanical system and a switch. For the 2025 One Hertz Challenge though, [jeremy.geppert] has eschewed such means. Instead his LED is always on, and is made to flash by interrupting its light beam with a gap once a second.

This mechanical solution is achieved via a disk with a hole in it, rotating once a second. This is driven from a gear mounted on a 4.8 RPM geared synchronous motor, and the hack lies in getting those gears right. They’re laser cut from ply, from an SVG generated using an online gear designer. The large gear sits on the motor and the small gear on the back of the disk, which is mounted on a bearing. When powered up it spins at 60 RPM, and the LED flashes thus once a second.

We like this entry for its lateral thinking simplicity. The awesome 2025 One Hertz Challenge is still ongoing, so there is still plenty of time for you to join the fun!

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Lamp Flashing Module Is Perfect For Automotive Use

October 1, 2022 by Lewin Day 17 Comments

Modern cars tend to have quite advanced lighting systems, all integrated under the control of the car’s computer. Back in the day, though, things like brake lights and indicators were all done with analog electronics. If your classic car needs a good old-fashioned flasher module, you might find this build from [DIY Guy Chris] useful.

It’s an all-analog build, with no need for microcontrollers or other advanced modern contrivances. Instead, a little bipolar PNP transistor and a beefier NPN MOSFET as an oscillator, charging and discharging a capacitor to create the desired flashing behavior. Changing the size of the main capacitor changes the flash rate. The MOSFET is chosen as running 12 volt bulbs requires a decent amount of current. The design as drawn is intended to run up to eight typical automotive bulbs, such as you might find in indicator lamps. However, [Chris] demonstrates the circuit with just four.

Flasher circuits were in regular use well into the 1990s. The original Mazda Miata has a very similar circuit tucked up under the dashboard to run the turn signals. These circuits can be hard to find for old cars, so building your own may be a useful workaround if you’re finding parts hard to come by. Video after the break.

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ESP32 Turned Handy SWD Flasher For NRF52 Chips

July 1, 2021 by Tom Nardi 9 Comments

Got an nRF52 or nRF51 device you need to flash? Got an ESP32 laying around collecting dust? If so, then firmware hacking extraordinaire [Aaron Christophel] has the open source code you need. His new project allows the affordable WiFi-enabled microcontroller to read and write to the internal flash of Nordic nRF52 series chips via their SWD interface. As long as you’ve got some jumper wires and a web browser, you’re good to go.

In the first video below [Aaron] demonstrates the technique with the PineTime smartwatch, but the process will be more or less the same regardless of what your target device is. Just connect the CLK and DIO lines to pins GPIO 21 and GPIO 19 of the ESP32, point your web browser to its address on the local network, and you’ll be presented with a straightforward user interface for reading and writing the chip’s flash.

As demonstrated in the second video, with a few more wires and a MOSFET, the ESP32 firmware is also able to perform a power glitch exploit on the chip that will allow you to read the contents of its flash even if the APPROTECT feature has been enabled. [Aaron] isn’t taking any credit for this technique though, pointing instead to the research performed by [LimitedResults] to explain the nuts and bolts of the attack.

We’re always excited when a message from [Aaron] hits the inbox, since more often that not it means another device has received an open source firmware replacement. From his earlier work with cheap fitness trackers to his wildly successful Bluetooth environmental sensor hacking, we don’t think this guy has ever seen a stock firmware that he didn’t want to immediately send to /dev/null.

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Jumbo LEDs Make For A Handy ATtiny Beacon

May 1, 2019 by Tom Nardi 3 Comments

Inspiration can come from anywhere. Sometimes it’s just a matter of seeing an interesting part that you want to fiddle around with badly enough that you end up developing a whole idea, and potentially product, around it. That’s how [Bobricius] found himself creating this very slick little warning beacon, and looking at the end result, we think he made the right decision.

The Kingbright DLC-6SRD “jumbo” LED is actually six individual emitters built into a plastic diffuser. Interfacing with the device is simple enough; each LED has its normal anode and cathode leg, all you need to do is power them up. What [Bobricius] has created is a simple PCB design that the DLC-6SRD can plug right into, complete with a 2032 coin cell holder on the opposite side.

Of course, just lighting up all six elements at the same time wouldn’t be very interesting. [Bobricius] is controlling them individually right off of the digital pins of an ATtiny10 with the help of some Charlieplexing. This makes all kinds of interesting patterns possible, and as demonstrated in the video after the break, the current iteration of the project uses some very simple code to “rotate” the LED as if it was the flasher on an emergency vehicle.

The addition of a few blinking LEDs can make a world of difference in terms of nighttime visibility, so a cheap stick-on module that adds such a distinctive light pattern could be a very important safety device. It could also be useful for UAVs, following the FAA’s new rules which would mandate anti-collision lights for night flying.

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Minimal Blinky Project Makes The Chip The Circuit Board

September 25, 2018 by Dan Maloney 16 Comments

We’ve got a thing for projects that have no real practical value but instead seek to answer a simple yet fundamental question: I wonder if I can do that? This dead-bug style 555 blinky light is one of those projects, undertaken just to see how small a circuit can be. Pretty small, as it turns out, and we bet it can get even smaller.

[Danko]’s minimal circuit is about as small as possible for the DIP version of the venerable 555 chip. The BOM is stripped to the bone: just the chip, three resistors, a capacitor, and an LED. All the discrete components are SMDs in 0805. The chip’s leads are bent around the package to form connections, and the SMDs bridge those “traces” to complete the circuit. [Danko] shows the build in step-by-step detail in the video below. There’s some fairly fine work here, but we can’t help wondering just how far down the scale this could be pushed. We know someone’s made a smaller blinky using a tiny microcontroller, but we’d love to see this tried with the BGA version of the chip which is only 1.4 mm on a side.

Cheers to [Danko] for trying this out and having some fun with an old chip. He seems to have a bit of a thing for the 555; check out this cute robot sculpture that’s built around the chip.

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Pavement Projection Provides Better Bicycle Visibility At Night

April 2, 2018 by Dan Maloney 67 Comments

Few would question the health benefits of ditching the car in favor of a bicycle ride to work — it’s good for the body, and it can be a refreshing relief from rat race commuting. But it’s not without its perils, especially when one works late and returns after dark. Most car versus bicycle accidents occur in the early evening, and most are attributed to drivers just not seeing cyclists in the waning light of day.

To decrease his odds of becoming a statistics and increase his time on two wheels, [Dave Schneider] decided to build a better bike light. Concerned mainly with getting clipped from the rear, and having discounted the commercially available rear-mounted blinkenlights and wheel-mounted persistence of vision displays as insufficiently visible, [Dave] looked for ways to give drivers as many cues as possible. Noticing that his POV light cast a nice ground effect, he came up with a pavement projecting display using four flashlights. The red LED lights are arranged to flash onto the roadway in sequence, using the bike’s motion to sweep out a sort of POV “bumper” to guide motorists around the bike. The flashlight batteries were replaced with wooden plugs wired to the Li-ion battery pack and DC-DC converter in the saddle bag, with an Arduino tasked with the flashing duty.

The picture above shows a long exposure of the lights in action, and it looks very effective. We can’t help but think of ways to improve this: perhaps one flashlight with a servo-controlled mirror? Or variable flashing frequency based on speed? Maybe moving the pavement projection up front for a head-down display would be a nice addition too.