In order for us to properly price our products we need to know exactly how long it takes to make things. This is fair for us and our customers. In addition, for our Sixty Second Shop videos, it’s important to know how long I’ve been rambling on.

Up to now we’ve been using things like cell phone stopwatches (which reset whenever a call comes in — ugh!) or just the clock on the wall. After wishing — for about the 100th time — for a big wall-mounted timer, I decided to build one.

I don’t need anything fancy. The timer merely needs to count up the seconds and display them in a very obvious way. Most of the individual steps we perform are under 15 minutes, so I could get by with a three digit display, counting from 1 to 999 seconds (about 16 minutes). Key features: Big. Easy to start/stop. Can survive shop conditions.

After building my LED Christmas Tree I realized I had exactly the correct circuit. A 555 timer could be used to (pretty accurately) tick off every second. As the seconds tick by, the CD4026 7 segment display driver would count up and display the values on the LED display.

Unlike the Christmas Tree, where I was using the 4026 as a pseudo random display, this time I’m actually using it for what it was intended — to translate counts / ticks to a 7 segment LED display. All I need to do is wire the correct LEDs to the appropriate outputs. Should be pretty easy.

If you own a digital clock, or just about any home gizmo, you’ve seen 7 segment displays. They are laid out like this:

When the CD4026 is at tick #3, it’s smart enough to translate that to the display. For example, if three was ticked, it would light up segments A, B, G, C, and D. The translation from counts / ticks to the display is handled by the chip itself. No thinking about logic, and no programming.

Okay, now I had an idea of how to drive the LEDs. Next I needed a display. Typically segment displays are pretty small (under an inch tall) and anything bigger is too expensive. Instead, I’d take a page out of the LEDKit Clock book and use discrete LEDs, wired in pairs, for the display.

First I found some open source clip art of 7 segment displays, resized a bit, and pasted three copies into a Word document. Then I printed it out. (My goal was to get them big enough to fill an 8.5 x 11 piece of paper, landscape.) Here is what it looked like:

At each segment I made two little marks to the left/right or top/bottom of the letter. These are where my LEDs will be located. I used two LEDs per segment because they can be simply wired together and means I don’t need baffles or other complexity between the segments. The holes are 5mm / 3/16″ (roughly) and fit standard 5 mm LEDs.

Note that I’ll be running the two LEDs in each segment in parallel. I don’t often advise this, as you could risk thermal runaway if one dies, but remember that I’m driving this with a CD4026 — a chip that is controlling the current for me. Chances of it blowing LEDs is pretty slim, especially since these are all from one batch.

I took the above template and spray glued it to a thin (5 mm) piece of plywood. Once dried a bit, I took it to my drill press and made all of the holes. The 3/16″ bit is just about the right size for 5mm LEDs. They fit snugly (sometimes requiring a second “wiggle” of the drill to get them in). Once drilled, I peeled off the template. Here’s the results (with LEDs):

For this timer I used super bright 5mm blue LEDs. Blue LEDs are usually very bright, which is what I want for the shop. This is a timer I need to see 25 feet away.

On the underside you can see all of the leads popping up. I’ll be wiring the two LEDs per segment together, then soldering short pieces of wire which will connect to the display board.

Remember: The letter (a to g) on the schematics is viewed from the front. On the back side, the horizontal letters (ex: B and F) are reversed. Don’t confuse yourself!

The LED wiring will probably be the most tedious part, since there will be 21 segments in all. Though, not much worse than the LED Christmas Tree, which had 20 LEDs wired in.

Next up, wiring the LEDs and then building the controller. The controller will be very similar to the Tree version — one 555 timer and three CD4026 display chips.

This version will cascade / carry down to the “downstream” chips. The 555 will trigger the first, and its output will feed the next chip, and so on. (In the Tree, the 555 triggered the clock of all three chips directly — in parallel.) I have to cascade/carry for this display because I want the numerals to automatically increment.  (This makes more sense if you take a look at some of the example data sheets.)

Also, I’ll probably use some potentiometers for the 555 timer instead of fixed resistors. Having a pot will allow me to make finer adjustments to the ticks. The 555 is pretty good at timing, but it depends of the outboard components (resistors and a capacitor) which can be affected by temperature and age. As long as it’s “about” a second a click I’ll be okay. This is a rough timer, so no need for a fancy clock chip or crystals or whatnot.

Here are a couple of video we made about the boxes. At the least, check out the Construction & Quality one.

We’re happy to announce that we have expanded our product line to include Owl Boxes. You can think of them as big bird boxes. The first model is designed for Eastern Screech Owls. It’s about 28″ tall with a 4″ opening. They came out pretty nicely and are very sturdy.

You can find more information at our business blog: Austin Kontore : Owl Boxes

I started on the controller board for the tree yesterday and finished up this morning. In the end I used the combination of a 555 (for timing) and CD4026 (display) chips. I did this because I wanted a simple stand-alone project without any programming. Here is a close-up of the controller board:

The 555 is in the upper left, with its timer capacitor and resistors. It’s timed to cycle about every second or so. The 555 basically sends “ticks” to the CD4026 chips, telling them to do something.

Why the CD4026? Well, those are normally used for 7 segment LED displays. You send X pulses to the chip and it displays digits 0 through 9. Very handy for clocks and meters and whatnot.

In my case, I wired in LEDs at random. As the chip cycles you end up with a pseudo random pattern. (Evelyn used these for the LED Firefly project.) The other nice benefit is that the chips are designed to drive LEDs, so you don’t need any current regulation (a resistor for each LED). This greatly reduces the part count.

The 4026 and the 555 also have wide voltage ratings, so you can feed them DC from 5 V to 15V and they are pretty happy. This is a great reason for beginners to play with these chips: They are forgiving (and cheap). Higher voltage means brighter LEDs, so I’m running on a 9-12V wall wart (it’s a POS, so the measured voltages is  a lot more than the rated).

I’m using one 555s output to drive all three CD4026′s in parallel. There’s room on the board to wire in a 555 for each CD4026 driver, but the display looks good the way it is. The circuit is pretty simple — the mass of wires is due to the number of LEDs (20) that I’m connecting.

The controller board gets mounted in the middle of the tree. All of the wires are connected via Molex connectors, so it’s easy to do work on the setup:

I used a couple of different colors, each of which is wired with the appropriate colored wire (red=red LED). In this setup we are using common cathode (ground). This is unlike the A6276 LED driver, which is common anode (positive / source). This is called sinking and sourcing. The CD4026 “sources”. The A6276 “sinks”.

The final product, lit. It can run off a 9V battery or a wall wart. Since I’m going to keep it on for a while, I’ve got it on the mains.

I just ran across this connector in the latest Newark flyer:

It allows you to terminate a DB9 connector with no crimping or soldering. It’s designed for field installation, but this would be really handy during prototyping.

For example, a lot of our LED displays and custom controllers (buttons, joysticks) use standard DB-9 cables. We use them because they are easy to work with, cheap, and pre-made cables are widely available in various lengths. Sure they are bulky at times, but great for hobby projects.

Up to now we have a couple pre-wired with some short (6-8″) leads, but then get flaky over time. I’m thinking we’ll get a couple of these instead, since the wires are connected via the terminal bocks with screws. Very handy.

You can find them at Newark for about $10 each. Not the cheapest, but you only need one or two for your workbench. Final products would likely be hard-wired–we’d use these during the prototyping phase.

DB9 Female Connector For Field Termination

They also have a HD15 (VGA) version.

Too bad they don’t have a male version of the DB9 — I could use one of each. Though, I could always use a gender changer.

There are many different electronic clock kits / projects out there. It seems that everyone who dabbles in electronics eventually builds some sort of clock. Maybe a binary with LEDs, maybe something electromechanical. Maybe it’s some sort of rite of passage. Like a cook needs to make Coq au Vin at least once.

Once in a while you come across a clock kit that actually looks interesting. This happened a while back when we bought & assembled the Chronulator. That was (and still is) a nice simple kit with an interesting (analog meter) display.

Today I see that another interesting clock kit is out: The Bulbdial from Evil Mad Science. These are the same folks who make the Peggy2 and the Meggy Jr.

The Bulbdial display the time by shining LEDs (forming a ring) toward a center post. The post creates shadows (like a sundial) which you use to read the time. It’s a neat idea and I’m glad to see it available in kit form. (The stacked circular PCBs alone are worth the price of admission.)

The kit, including acrylic face plates, is $85. For some people this may seem high, for me it is ridiculously low. As someone who has spent a great deal of time pricing materials and labor over the past 6 months, they must either be getting really good discounts on the PCBs and plastics, or are taking a bit hit in profits. Make it up in quantities, I guess, but still.

If this kit is anything like the other two I’ve built (Peggy & Meggy) it will be excellent. The folks at Evil Mad Science do an outstanding job packaging and presenting their work. The instructions are clear and logical, even for the more complicated projects. (If you want to see the right way to write an electronics kit assembly guide, look to their work.)

This kit requires some soldering skills. Looking at it, I wouldn’t recommend it for first time kit builders, but if you’ve made a couple of kits already you’ll be fine. If you are unsure, then get one of their neat Larson Scanners ($13) or their Menorahs ($14) to practice on and then put the clock together.

If you are looking for interesting electronics kits, with high build quality, and easy to understand instructions, then take a look at their work. Highly recommended.

Behind every cool LED display is a lot of wiring. Here is the rear view of the tree with wires soldered to the LEDs:

In this design we are running common cathode (negative). That’s a black wire that runs between every LED. Then each LED gets its own wire. Unlike simple strings of lights, each of these LEDs is individually controlled. This means that you can’t wire them in series (one wire lights all).

The display board will be in the middle of the tree. I’m going to run this off a battery (9V).