Tag Archives: programming

Binary Clock, Part 2

The long awaited part 2 of this blog post has finally arrived! But first, a video, in case the whole “reading” thing isn’t your bag…

Though I’ve been tinkering on this project for the past two years, I decided to write it up to coincide with the outrageous arrest of 14 year old tinkerer Ahmed Mohamed who was hand cuffed because his teacher thought his electronic clock project looked like a bomb. This binary clock project of mine ended up being a personal electronic circuit design introduction course. You can download all the relevant files here if you want to make your own.
I forgot what the original inspiration was but what I’m ending up with is a working binary clock on a custom printed circuit board. Ultimately, this project will involve fiber optics inside polished cement for a unique time piece but we’re not there yet… Here’s what I learned so far:

Bit shifters

A binary clock needs 20 individual blinky things and the arduino has less than that, so I needed to figure out a way to create more individually addressable outputs. The solution I found is a the 74HC595N chip that can turn two inputs into 8. In fact, you can wire them in series and they can provide you with any number of outputs in multiples of 8. I decided to use one to drive the hours display, one for the minutes, and one for the seconds.

There are tons of tutorials for them so it was fairly straight forward to get it working.

Keeping time

While you can make a timer with just an arduino, it is not very accurate and it has no way to keep the clock going if you unplug the power. I used a rtc1307 chip which is designed for just this purpose. It keeps time accurately and uses a small battery to continue keeping time when the power is disconnected.

Again, there is an arduino library available and a good amount of tutorials out there so it wasn’t too hard to test it and incorporate it in the build.

Removing the arduino

Eventually, since I wanted to end up with a single circuit board, I didn’t want to have to plug anyting into an arduino. Once again, the internet is a wonderful resource which allowed me to figure out how put only the arduino components I needed onto a bread board. I can upload the code onto the chip by putting it on an arduino, and then pull it off of there to mount it directly onto the breadboard.

Code

The clock can be set to one of 4 modes: display time, set hours, set minutes or set seconds. There are two buttons. One button toggles between all the different modes, while the other increments the count of the hours, minutes, and seconds when they are in their respective mode.

Schematic and board

Once the breadboard was working, I set out to sketch the circuit in Fritzing. While it’s not quite as intimidating as EAGLE cad, I ended up using the latter after running into some limitations with the former (I don’t remember what they were). There was a lot for me to learn there but, in the end, it’s conceptually pretty simple: all the pieces have to be connected together correctly. It’s just another way to represent the circuit. Once that was done, I started with the board. I laid out all the components and let the software automatically figure out how to create the correct traces.
One cool thing is that if you choose the correct electronic components in the software, all the size and shapes are properly represented when you are designing the board. It’s a huge pain in the ass to sort through all the libraries of components, though, specially when you don’t know what all the specs mean.

The eagle cad files are included in the download file at the top of this page.

Manufacturing the board

Super simple: just go online and find a service that will manufacture them. For this project, I used oshpark.com and dirtypcbs.com, which allow you to upload your designs right out of EAGLE cad. After a few weeks, you get your board in the mail, ready for you to solder the components on. I order my components from mouser.com, which allows you to save a collection of various components into a project specific list. Again, finding the right components amongst the tens of thousands they have available is really time consuming and annoying. But now, I have my parts list so I never have to go through that again if I want to solder up new versions of the board. The list of parts in included in the download file at the top of this page.

The ugly truth

If you were paying attention, you no doubt noticed in the preceding paragraph that I used two board manufacturers. That is because the first board layouts I had printed actually had shorts. I suppose it’s probably not that uncommon, but it’s really frustrating to upload your designs, order the boards, wait for them to be delivered, spend all this time soldering the board to find out it doesn’t work, and then it can be challenging to figure out where the wires are getting crossed. In the end, I spent about $150 on boards and parts that ended up not working. I guess that’s the cost of learning… My first two board designs were ordered through Oshpark, and the minimum order was 3, for about $50. The third order was done on dirtypcbs and was $25 for 10 boards. They feel cheaper and took forever to get delivered but you sure can’t beat the price.

Flashing Arduino bootloader with Teensy 2.0

What

If, like me, you want to flash the arduino bootloader onto some blank ATMEGA328 chips on a breadboard and only have a teensy 2.0 on hand (because you’ve short circuited all the working ATMEGA chips you had and so can’t use your arduino), and, unlike me, you don’t have hours to spare trying all freaking possible software/hardware/wiring combination to get it working, here’s what worked for me. Also, since I didn’t want to bother with the crystal, capacitors and resistor, I went for the minimal setup.

Why

Because a chip with the bootloader already loaded costs $5 and a chip without costs $2. And also, really, just because…

How

  • I used arduino 1.0.6 on a macbook running osX 10.6 (For those running Yosemite, there are documented issues recognizing the USB port)
  • I downloaded Breadboard1-0-x.zip and installed the contained breadboard directory in the “hardware” folder of my sketches.
  • In arduino, load the ArduinoISP sketch from the examples, change the LED pin to 11 (#define LED_HB 11), select Teensy 2.0 as you board and upload the sketch
  • Wire up the ATMEGA as follows.
  • Relaunch arduino and for your board, select Tools > Boards > “ATmega328 on a breadboard (8 MHz internal clock)” and Tools > Programmer > “Arduino as ISP”
  • Select Tools > Burn Bootloader
  • Done!
  • This is basically the steps outlined in the official Arduino website, except for changing the LED pin to 11 in the ArduinoISP sketch and wiring the ATMEGA to the proper pins on the Teensy 2.0. (Note that you don’t even have to change the code to reflect the different pin numbers since they are referred to by their function rather than their number).

There

Here’s a picture and a schematic…

^[strange]+6\s[regx]+5\s[obseion]+9$

I find regular expressions obtuse, maddening, and at the same time, strangely compelling. For those who don’t know, “regular expressions” (usually referred to as “regex”) is a common way for most computer programs to search text for particular patterns of characters, like for example a date or an address. Regex gives you access to atoms that represent individual character (“a”, “6”, “#”, etc…) or general character types (digits, symbols, uppercase…), as well as a concise grammar defining how these characters appear. Regex is a set of small blocks with specific rules that define how to put all these blocks together to represent something bigger.

A quick example

How to match a date like 2014/12/24?
Digits are represented like this: \d so the following regex will represent any character from 0 to 9:
\d
What if you are looking for a series of 4 digits? You could do this:
\d\d\d\d
But it can get a little heavy if you are looking for 200 digits, so you can use the following notation:
\d{4}
Okay, so now you have matched the first 4 digits, how about matching the “/” character? In this case, since it’s just a specific character, just go ahead and type it in:
\d{4}/
Then match 2 digits, another “/” and two more digits:
\d{4}/\d{2}/\d{2}

It’s a mental puzzle that requires you to visualize how patterns can be broken down into concise nuggets of representative abstraction.

Regulex

The following web site creates a diagram out of a regex expression to give you a useful visual graphic depiction of the logic.

Regexpress

This next one uses similar visuals but allows you to build the expression by stringing along icons that represent the patterns you are looking for.

Regviz

Here’s another one that doesn’t use fancy charts and graphics but it does allow you yo see the matches in real time with text you specify.

How to get a 9 year old interested in programming

Osx has a nifty command line speech synthesizer called “say”. It allows you to type some text and hear it “spoken” by the ubiquitous synthesized robotic voice. First, open the terminal and show him how it works by typing:
say "hello, my name is Robert"
Then show him that you can type different sentences and let him play with that until he gets the hang of it. Make sure to include enough potty humor to ensure sufficient hilarity:
say "Even though I am a computer, I sometimes talk about farts."
That should get his attention. You can also include question marks and nonsensical words for extra extra fun:
say "Are you some kind of flarpy nunckenbarf?"
The next step is to introduce the concept of variables:
friend="John"
say "$friend is a complete idiot"
friend="My hamburger"
say "$friend is a complete idiot"

By this time, tears of laughter should be streaming down his face, but don’t let it stop you. This is where the comedic potential really starts paying off with the introduction of the “for” loop.
for friend in "alfred" "max"
do
say "$friend is a fizzlebutt"
done

And then show him how to pause between the sentences
for friend in "alfred" "max"
do
say "$friend is a fizzlebutt"
sleep 1
done

Finally, once he finally peels himself off the floor and catches his breath, you apply the final coup-de-grace with the help of the “if” statement:
for friend in "alfred" "max" "frank" "dave"
do
if [ "$friend" != "max" ]
then
say "$friend is a total moron"
sleep 1
else
say "$friend has bad breath"
sleep 1
fi
done

After you share these intoxicatingly powerful instruments of distraction with your son, I suggest you steer clear of the technology teacher at the school.