Fubarino Contest: Persistence of Vision clock


The best part of these contests is that we get people to actually show off what they’ve been working on! Check out the POV clock which was sent in by [Taciuc]. He doesn’t have a webpage for it, but he did send a video which you can see after the break.

The project is a home-etched PCB with a long row or surface mount LEDs. The board is spun by a stepper motor which takes a little while to stabilize. But once it does it’s a twirling package of awesomeness. A PIC 16F628 drives the device, with a separate RTC chip to keep time. There’s also an IR receiver to facilitate user control. Our URL is displayed on the clock face itself and we think it’s always shown. But there is an easter egg in the code itself. If you try to dump the firmware from the chip you’ll see our web address in the hex output. Here’s his project archive if you want to the HEX, ASM and DipTrace schematic.

This is an entry in the Fubarino Contest for a chance at one of the 20 Fubarino SD boards which Microchip has put up as prizes!

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Persistence of Vision Planetary Map

POV planetary map

Looking at the looping GIF above you’re probably thinking, oh, another hard drive POV setup… Well… Not quite.

This is one of [Dev’s] latest projects, and it is a planetary map that shows the angular positions of all 8 of the major celestial bodies from any given date between 1800 and 2050. It’s also capable of showing analogue clock hands, the phases of the moon, and other simple graphics.

The main unit is a hard disk, but [Dev] milled off many of the features on it to give it a more exposed, purpose-built look. He designed the LED bearing PCB from scratch using EagleCAD, which sits on the back of the drive, with the spindle poking through. It has 8 rings of 5 surface mounted LEDs, which shine through opaque plastic diffuser rings that he printed using Shapeways — they feature small recesses to fit snugly on the board over the LEDs. On the top level is a 1mm thick black disc of some unknown material that [Dev] had sitting around, which now has 8 holes machined into it in the exact position of the LEDs.

A Cortex-M0 drives the LEDs using an LPCXpresso board which allows the LEDs to sit across only one byte of a hardware I/O port. On the software end, each rotation of the disk is segmented into three hundred and sixty 1 degree slices. This system allows him to achieve a circular resolution of 8×360 pixels at 25 frames per second. Not bad for a persistence of vision device!

Stick around after the break to see the rather entertaining demo video of the device.

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[Kyle] wanted to try something new. A Persistence of Vision Clock using a CD-ROM drive.

We have covered lots of POV Clocks that make use of hard drives, but we think this is the first time we have seen a CD-ROM drive used instead. [Kyle] points out that CD-ROM drives are typically much quieter than hard drives, which is the main reason he chose the CD-ROM route.

At the heart of this project is a good old ATMEGA168 and an RGB LED strip for the lights. To measure and maintain the rotational speed of the clock [Kyle] used an IR photodiode that detects a reference mark on the disc. An elegant build of a classic POV Clock, with a new twist!

The cool thing about this project is he did not actually use the CD-ROM drive like you think he would — he chucked the spindle motor and instead is spinning the disk using the tray ejection motor! He did this so he could control the motor by PWM straight off the microcontroller, whereas the spindle motor would require an IC and a varying control signal with specific voltage amplitudes.

He also experimented with different backgrounds and background lighting, which you can see in the video after the break!

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Ghostly images captured only on camera

is that a logo

A while back our good buddy [Ch00f] built a QR code clock, unreadable to both humans and computers. A human couldn’t read the clock because of the digital nature of a QR code, and because the clock used persistence of vision in driving the LEDs, a digital camera can’t capture all the pixels in the QR code at the same time. It’s a highly useless but impressive art piece. Now, [Ch00f] is turning that build on its head. He created a rudimentary display that is invisible to the human eye, but easily detected with a digital camera.

This build exploits a basic property of CMOS digital cameras – the rolling shutter. Because it takes time to get pixels off a modern digital image sensor, each picture is actual a composite of many different strips, each taken slightly out of sequence. You can see this for yourself by taking a picture of something rotating very fast with your camera phone; a picture of an airplane propeller will make the blades appear curved, or look like [Dr. Seuss] has an aeronautical engineering degree.

To create his display, [Ch00f] found a few inexpensive fiber optic lights. By aligning a few of these into columns and lighting them up in a precise sequence, he can exploit the rolling shutter and make an image appear. To the human eye, it looks like a solid wall of illuminated fiber optics.

As for how practical this build is, [Ch00f] says not much. For cell phone cameras, you’d need to have a very, very short exposure time for this to work. The only way to do that is to make this display unbelievably bright, or just put it out in the sun. We can’t see that being practical for any potential use case, but we’d be more than happy to see a large-scale attempt at displaying images with this technique.

POV clock spins light filter instead of LEDs

This hard-drive based POV clock is a treasure trove of great design choices. Now, we’ve seen a bunch of spinning clock builds. Several of the hard drive versions use slits cut in the platters to create a display by illuminating an LED behind those slits at just the right moment. This is a similar idea but [Jason Hotchkiss] ditched the platters all together and replaced them with a light filter. The filter disc has digits 0-9 as well as a colon (not seen above because the colons blink each second). As this disc spins, the Arduino compatible controller lights up LEDs in the eight digital positions to illuminate the correct number.

The filter is made from an etched copper-clad disc. This is a great choice because the fiberglass substrate is strong, light weight, translucent, and available. The filter idea also means you don’t need to get power or data to a spinning platform. [Jason] has also designed a very impressive controller board that is the same size as the footprint of the laptop hard drive he’s using. Check out the video after the break to see his description of what went into the hardware choices he arrived upon. Continue reading “POV clock spins light filter instead of LEDs”

Bending a printer control board to output POV messages

Confronted with the issue of finding a use for his mounting pile of junk electronics, [Rue] set out to build a persistence of vision device using a hardware state machine. We have a suspicion that his original link may go down if there’s too much traffic so here’s a cached link just in case.

Any board that is MSC-51 or MCS-48 based would have worked for his purposes. This is because the addressing scheme of the hardware makes it an easy hack. The image above shows him cutting off the processor from this board. It was chosen because of a 74HC373; it was a mistake at first but since it’s pin compatible with the 74HC374 that he needed a simple swap did the trick. From there a clock source was added, and the address information necessary to display the message was burned into an EEPROM.

Step twelve of his writeup shows a Morse Code message created by attaching the board to a broomstick and twirling it around in an arc. We took  just a minute to decode the message and believe it’s a shout-out to Hackaday. Nice, thanks for reading [Rue]!

Reverse engineering the Icebreaker POV toy

[Ch00f] spent some serious time figuring out how the Icebreaker POV toy works. This is a pretty cool device about the size of a toothbrush holder. It’s in a clear plastic case, which lets the row of 32 surface mount LEDs shine through. But making light isn’t their only function. You can use the device to scan in a high-contrast design, then ‘play it back’ using the persistence of vision display properties of the LED strip.

Perhaps the biggest question on [Ch00f’s] mind was how the sensing is done. He made a series of observations, then started monkeying around with the LEDs to investigate them. It seems that one LED is lit up while the ones around it are used as light sensors. This becomes more confusing once he realized that the display was multiplexed.

His write-up includes a collection of schematics that can be pieced together to conceptualize the entire circuit. The image above was taken during this process, using an LED to check the connections on a part. This let him prove that it’s an N-channel MOSFET. He plans to take what learned and roll it into his own project.

[via Reddit]