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Binary/POV custom wristwatch

All > Tech > Inventions > Binary/POV custom wristwatch by natetrue

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Kits and preassembled watches are available here.

Recently my good friend Andru Edwards and I got into a heated discussion about watches. My old Fossil Abacus PalmOS watch was getting pretty worn, and I was shopping around for new watches. Having seen a cool video-playing watch over at Gear Live, I was thinking I might upgrade to one of those, purely for geek-bling factor.

Andru, being more grounded than I am as far as fashion is concerned, suggested that the video playing watches I was looking at (I was searching DealExtreme for MP4 Watch) were all profoundly lame. So he told me to go look at the TokyoFlash watches which tell time using discrete LEDs rather than using LCDs or large pixel counts.

Of course, the TokyoFlash watches look amazing. But I wasn't planning to spend $180 on one. I mean, even the video watches maxed out at like $60.

So what does a maker do when he wants something but doesn't want to buy it? He makes a knock-off! I mean, it's much more respectable than that, because of how much work goes into it.

I decided to go with a binary representation, since it would require the fewest LEDs to represent the most information.

Watch features

Binary time display

POV (persistence-of-vision) display when swiped in the air

Super-bright flashlight mode

Want to buy one instead of making it, or buy all the parts from one place as a kit? Check out the Buy page. Got all the parts already or need a parts list? Skip to the Assembly section.

Here's how I made it:

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I started paying with the board layout on a big piece of pre-punched PCB.

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Erythema approved of the design, and I made the first prototype.

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Built on a leather band that my sister had given me, the first prototype used a battery from a Bluetooth headset, taped to the bottom of the band. There was no charger in the prototype; fortunately the battery lasted the whole prototyping stage.

It also used a ceramic resonator as its timebase, as I didn't have the necessary 32 KHz crystal nor the 33pF capacitors to have the accurate crystal timer.

That was just a detail, though. With the prototype I could develop the timekeeping logic and the display details.

I figured the watch should be enclosed somehow, rather than just being a bare board. So I trolled my local fabric store for some material. My eyes fell on this faux-leather brown vinyl with a nice soft cloth backing. It was fairly expensive but I did not need much of it.

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I built a second board with the LEDs elevated somewhat, and punched some holes in a big piece to match the LED layout. The PIC needed to be on the outside, so that I could flash it. If I wanted it below the covering, I would have had to solder it directly to the board instead of using a socket.

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There you see the detail of how the LEDs poke through the covering. The buttons do not poke through, but you can still push them.

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I had to learn to sew for this part. Hemming something that small is very difficult and I did not do it well.

I decided to use push snaps for now but I think a buckle with holes like a normal watch would be better for adjustability.

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Here's how it looks with the cover sewn on. It's pretty thin because the battery is along the band (It's on the left of this photo). The USB port is on the back:

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The USB port is only for charging (the PIC16LF628A is not fast enough to implement USB). It feeds power to a MAX1555 Lithium-ion battery charger chip, which is perfect because it needs no external parts (they say it should have capacitors on its terminals but screw that).

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That little chip is very small so it's very difficult to solder to.

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I decided to go with a 70mAh Li-ion polymer battery, which should power the watch for a pretty long time. Additionally it can supply much larger currents than standard long-life lithium batteries, which enables me to have a bright flashlight mode for the watch.

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The battery is very small, too, which is perfect for a watch.

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I also developed a POV (persistence of vision) capability for showing the time to others, as it's hard to explain binary to people (especially dumb people).

The concept of a POV display is very simple - using a single row of 5 LEDs, the PIC displays each column of the display in turn. When the watch is swiped through the air, each column is spatially separated from the last, allowing a "larger" display area to show with only 5 LEDs.


Assembly

Ready to make your own? Great! Here's what you need. All of these elements are included in the POV watch kit which you may have noticed you can buy from me.

Some pre-tinned hookup wire

A prepunched PCB with standard hole spacing, 14 holes by 9 holes, and a MAX1555 presoldered

An 18-pin socket

A PIC16LF628A programmed with the watch HEX file

A 32.768 kilohertz watch crystal

Two 33pF capacitors

Three 10 kilohm resistors

Fourteen 3mm LEDs (recommended 3mm Bright White LEDs)

3 small pushbuttons

A Mini-USB B-type socket

A MAX1555 Li-ion charging IC (in the kits, it will be presoldered to the board)

A 70mAh lithium-ion polymer battery

Materials for a watch band

A USB-A to Mini-B cable for charging

Got all that? Let's get started!

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Let's begin by placing the 18-pin socket, the 14 LEDs, and the buttons as shown. Insert the components through the NON-COPPER side of the board, so that the leads come out the COPPER side. Make sure the board is oriented so that the MAX1555 on the board is behind the buttons and not behind the IC socket.

You may wish to elevate the LEDs if you're making an enclosure, so they stick up past the buttons and the IC socket. Keep your final container in mind. If you're building from a full kit, you'll want to have the LEDs elevated at least 2 millimeters above where they'd normally sit, and you will want to secure them somehow so they don't bend side to side.

Remember the LEDs are polarized so make sure the cathode leads (the shorter ones) are toward the buttons on the board. Solder the leads to the back side and clip them appropriately.

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Now, flip the board over, and solder on the two capacitors as shown, along with the crystal. Make it so that the crystal comes around the top of the board to take up as little space as possible.

The MAX1555 is VERY tricky to solder. Make sure you have a magnifying glass on hand to observe your work. As shown, one of the pins is not needed, and two of the pins are soldered together to one of the button terminals (this is a ground connection). Make sure you don't bridge any of the other pins with solder!

Since soldering the 1555 is so difficult and the thing is so small, kits ordered from me will come with this part already soldered in.

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Next is the row wiring. The PIC powers the rows by pulling their pins low. Double-check now that you have put in the LEDs correctly, with their cathodes all connected with the row wires.

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Predictably, the column wiring comes next. This is less pretty but it's gotta be done. The PIC activates each column by pulling the column pin high. Using row and column addressing lets us address 14 LEDs with only 8 I/O pins. Theoretically we could address up to 32 LEDs with those 8 pins (even more with external circuitry) but we only need 14 (reader's exercise: how would we wire 32 LEDs to only 8 pins and be able to light up each one in turn, with no additional components?). If this design was pin-grubbing we could use as few as 6 I/O pins for the 14 LEDs but it doesn't have to be that complicated.

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Now to wire up the buttons and power. Simple enough. The red wires are the positive wires, and the black ones are negative. Consult the following image for the correct polarity of the USB connector.

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The negative lead is the leftmost one, and the positive is the rightmost. You can cut off the middle three, as that will make soldering much easier.

Using your watch

What good is a watch if you can't use it? When the watch is first powered on it will think it's 6:57 PM, since being 12:00 AM results in no lights of the display being on and you'll think it's broken. The display automatically turns off after 10 seconds when in clock or POV mode, so press any button to turn it on.

Here's how to tell time in binary mode:

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Each row's right four LEDs is a portion of the time. To tell what number it is, sum up the values of the lights that are on. For example:

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Here you see the upper-left LED is on. That means the time is PM as opposed to AM.

In the Hours area (the top row, right 4 LEDs), only the LED with the value 4 is on. So the hour is 4 PM.

In the Tens of Minutes area (middle row) the LED with the value 4 is on. So the tens of minutes is 4 also.

In the Ones of Minutes, we have the LED with the value 1. So the ones of minutes is 1.

That makes it 4:41 PM.

Watch modes
The watch has several different modes. You can switch modes by holding the center button until the mode changes, then releasing. You can always return to Clock mode by pressing and holding the center button until the watch returns to Clock mode. All modes except Flashlight mode will turn the watch off after 10 seconds. To wake the watch, hit any button.

Do not look directly into the LEDs during Flashlight mode, as they will leave a lasting image on your eye that may interfere with vision for several minutes.

Modes:

Binary Clock mode

POV clock mode

Set hours mode

Set tens of minutes mode

Set ones of minutes mode

Binary counting mode

Button diagnostic mode

Flashlight mode - this mode is last, because technically the watch turns off while it's in this mode

The last two modes aren't very useful and are not interactive in any way.

In Binary Clock mode, you can hold the left and middle buttons together to reduce the brightness, and the right and middle buttons together to increase it.

Press the left and right buttons at the same time to shortcut to Flashlight mode.

In POV clock mode, you swipe your wrist through the air (bringing the watch downward) to write the time in the air.

When in one of the setting modes, pressing left or right will decrease or increase the current number, respectively. To exit setting mode, press and hold the center button until it returns to clock mode. To go to the next setting mode, press and hold the center button until the mode changes, then release.

I hope you enjoyed reading about my watch as much as I enjoyed making it.

Be sure to check out my other stuff!

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