Cheap Projector Tells Time, Invades Space

Building a video projector isn’t something that most people do casually, but [Dominic Buchstaller] isn’t most people. As part of an ongoing street art  project, he built a rather neat scrap video projector/bedside lamp/clock device he calls Great Balls of Fire. It is made from a Nokia cell phone screen and a small projector mechanism, mounted inside a frosted glass light sphere.

One of the most interesting parts of the build is the projector mechanism. Rather than build one from scratch or tear apart an expensive Pico projector, [Dominic] found another source: a cheap car logo projector from eBay. These are designed to show a car manufacturer logo on the ground when you open your car door. It came with all of the parts he needed, including an LED light source and optics. He tore that apart and replaced the car logo with the phone screen, creating a very cheap projector. It isn’t that bright, but it is bright enough that when he mounted it inside the glass sphere, it could project the time and the odd space invader. It’s a great example of how sometimes it makes sense to look for a cheap solution rather than a free one: buying the car logo projector saved him a lot of hassle in building the optics. [Dominic] was also responsible for this awesome old-school tube radio hack, where he replaced the guts of an old radio with an internet radio player.

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Embed with Elliot: We Don’t Need No Stinkin’ RTCs

A lot of microcontroller projects out there need some sense of wall-clock time. Whether you’re making (yet another) crazy clock, logging data, or just counting down the time left for your tea to steep, having access to human time is key.

The simplest solution is to grab a real-time-clock (RTC) IC or module. And there’s good reason to do so, because keeping accurate time over long periods is very hard. One second per day is 1/86,400 or around eleven and a half parts per million (ppm), and it’s tricky to beat twenty ppm without serious engineering.

Chronodot uses a Maxim TXCO
Chronodot uses a Maxim TXCO

Good RTC ICs like Maxim’s DS3231, used in the Chronodot, can do that. They use temperature correction logic and a crystal oscillator to get as accurate as five parts per million, or under half a second per day. They even have internal calendar functions, taking care of leap years and the day of the week and so on. The downside is the cost: temperature-compensated RTCs cost around $10 in single quantity, which can break the budget for some simple hacks or installations where multiple modules are needed. But there is a very suitable alternative.

What we’re looking for is a middle way: a wall-time solution for a microcontroller project that won’t break the bank (free would be ideal) but that performs pretty well over long periods of time under mellow environmental conditions. The kind of thing you’d use for a clock in your office. We’ll first look at the “obvious” contender, a plain-crystal oscillator solution, and then move on to something experimental and touchy, but free and essentially perfectly accurate over the long term: using power-line frequency as a standard.

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Modern Spin on an Old Technology

It seems that the longer a technology has been around, the more likely it is that all of the ideas and uses for that technology will be fleshed out. For something that’s been around for around 5500 years it must be especially rare to teach an old dog new tricks, but [Sebastian] has built a sundial that’s different from any we’ve ever seen.

Once done with all of the math for the sundial to compute its angles and true north based on his latitude and longitude, [Sebastian] used Autodesk Inventor to create a model. From there it was 3D printed, but the interesting part here is that the 3D printer allowed for him to leave recesses for numbers in the sundial. The numbers are arranged at such angles inside the sundial so that when it’s a particular hour, the number of the hour shines through the shadow of the sundial which creates a very unique effect. This would be pretty difficult to do with any machine tools but is easily accomplished via 3D printing.

[Sebastian] wanted a way to appreciate the beauty of time, and he’s certainly accomplished that with this new take on  the sundial! He also wonders what it would be like if there was a giant one in a park. This may also be the first actual sundial build we’ve featured. What does that mean? Check out this non-pv, sun-powered clock that isn’t a sundial.

Thanks to [Todd] for the tip!

A Colorful Clock for Toddlers

[Don] and his wife were looking for a way to teach their two-year old daughter how to tell time. She understood the difference between day and night, but she wasn’t old enough to really comprehend telling the actual time. [Don’s] solution was to simplify the problem by breaking time down into colored chunks representing different tasks or activities. For example, if the clock is yellow that might indicate that it’s time to play. If it’s purple, then it’s time to clean up your room.

[Don] started with a small, battery operated $10 clock from a local retailer. The simple clock had a digital readout with some spare room inside the case for extra components. It was also heavy enough to stay put on the counter or on a shelf. Don opened up the clock and got to work with his Dremel to free up some extra space. He then added a ShiftBrite module as a back light. The ShiftBrite is a high-brightness LED module that is controllable via Serial. This allows [Don] to set the back light to any color he wants.

[Don] already had a Raspberry Pi running his DIY baby monitor, so he opted to just hijack the same device to control the ShiftBrite. [Don] started out using a Hive13 GitHub repo to control the LED, but he found that it wasn’t suitable for this project. He ended up forking the project and altering it. His alterations allow him to set specific colors and then exit the program by typing a single command into the command line.

The color of the ShiftBrite is changed according to a schedule defined in the system’s crontab. [Don] installed Minicron, which provides a nice web interface to make it more pleasant to alter the cron job’s on the system. Now [Don] can easily adjust his daughter’s schedule via web page as needed.


Binary Clock Would Make Doc Brown Proud

[Brett] was looking for a way to improve on an old binary clock project from 1996. His original clock used green LEDs to denote between a one or a zero. If the LED was lit up, that indicated a one. The problem was that the LEDs were too dim to be able to read them accurately from afar. He’s been wanting to improve on his project using seven segment displays, but until recently it has been cost prohibitive.

[Brett] wanted his new project to use 24 seven segment displays. Three rows of eight displays. To build something like this from basic components would require the ability to switch many different LEDs for each of the seven segment displays. [Brett] instead decided to make things easier by using seven segment display modules available from Tindie. These modules each contain eight displays and are controllable via a single serial line.

The clock’s brain is an ATmega328 running Arduino. The controller keeps accurate time using a DCF77 receiver module and a DCF77 Arduino library. The clock comes with three display modes. [Brett] didn’t want and physical buttons on his beautiful new clock, so he opted to use remote control instead. The Arduino is connected to a 433MHz receiver, which came paired with a small remote. Now [Brett] can change display modes using a remote control.

A secondary monochrome LCD display is used to display debugging information. It displays the time and date in a more easily readable format, as well as time sync information, signal quality, and other useful information. The whole thing is housed in a sleek black case, giving it a professional look.

Hacklet 18 – Tick Tock, it’s Time for Clocks


In three words, Hackers love clocks. Not only do we think that digital watches are still a pretty neat idea, we love all manner of timepieces. This episode of The Hacklet focuses on the clock projects we’ve found over on

xkcdHardwareWe start with [rawe] and [tabascoeye], who both put the famous XKCD “now” clock into hardware. [tabascoeye] used a stepper motor in his xkcd world clock. [rawe] didn’t have any steppers handy, so he grabbed a cheap wall clock from Ikea for his clock in hardware. The now clock needs a 24 hour movement. Ikea only sells 12 hour movements, so [rawe] hacked in a 555 and some logic to divide the clock’s crystal by two. He’s currently using an EEVblog uCurrent to verify his modified clockwork consumes about half a milliwatt.

touchscreenclockNext up is [Craig Bonsignore] and his Touchscreen Alarm Clock. [Craig] got sick of store-bought alarm clocks, so he built his own. Then he modified it, added a few features, and kept building! The current incarnation of the clock has a pretty novel interface: a touchscreen over a bicolor LED matrix. The rest of the clock consists of an Arduino, an Adafruit Wave shield, and a Macetech Chronodot. [Craig] is currently mashing up these open source designs and building a single Arduino shield for his clock.

irisledclock[Warren Janssens] took the minimalist route with The Iris Clock. Iris is a ring of WS2812 RGB LEDs. The LEDs are mounted behind a wall colored piece of wood in such a way that you can only see their glow on the clock frame and the wall beyond it. This helps a with the eye searing effect WS2812s can have when viewed directly – even when dimmed with PWM. The code is mainly C with some AVR assembly thrown in to control the LEDs. [Warren] has given Iris 8 different time modes, from hour/minute/second to percentage of day with sunrise and sunset markers. With so many modes, the only hard part is knowing how to read the time Iris is displaying!

stargate[David Hopkins] also built a ring clock. His Stargate LED Clock not only tells time, but is a great replica of the Stargate from the TV series. [David] used four Adafruit WS2812 Neopixel segments to build a full 60 RGB LED ring. The Stargate runs on an Arduino nano with a real-time clock chip to keep accurate time. A photoresistor allows the Stargate to automatically dim at night. With some slick programming [David] added everything from a visual hourly “chime” to a smooth fade from LED to LED.

bendulum[dehne1] gives us something completely different with The Bendulum Clock. A bendulum is [dehne1’s] own creation consisting of an inverted pendulum built without a pivot. The inverted pendulum swings by bending along its length. In [dehne1’s] design, the bendulum is made out of a spring steel strip rescued from a car windshield wiper. The Bendulum doesn’t have a mechanical escapement, but an electromagnet sensed and driven by an Arduino. The amazing part of this project is that  [dehne1] isn’t using a real-time clock chip. The standard 8MHz Arduino resonator is calibrated over various temperatures, then used to calibrate the bendulum itself. The result is a clock that can be accurate within 1 minute each day. [dehne1] mounted his clock inside a custom wood case. We think it looks great, and want one for Hackaday HQ!

We’ve used enough clock ticks for this episode of The Hacklet. As always, see you next week. Same hack time, same hack channel, bringing you the best of!

Still want more? Check out our Timepiece List!

Wristwatch measures your perception of time; also tells time

This wristwatch is hiding a lot of features in its hardware and its software. It’s called the TicTocTrac and it’s a Senior project for a pair of students at Cornell University. Judging from the sheer volume and quality of the project documentation we wonder if someone has a science writing career ahead of them? Be we digress… It’s a clock and we love it!

First off, this does more than just tell the time. In fact, that’s almost an ancillary function in this case. The wristwatch is more of a metering device to record your own time-based behaviors. Find yourself checking your watch frequently as the lunch break approaches? This watch records that activity and you can later graph the data. This allows you to analyze how you percieve the passage of time. The more often you check the time, the slower you feel time progressing. The documentation does a much better job of describing this than we have time for, so check it out.

On the hardware side of things we’re quite impressed. The housing is 3D printed. It hides two half-circle PCBs below the full-circle PCB face plate. The half-boards leave space for a tiny rechargeable battery, and host a vibrating motor and RTC chip. Instead of using buttons, there’s a piezo sensor which detects when you tap on the top of the watch.