Tag Archive | "arduino project"

Blinky the one-eyed clock

In this tutorial you learn how to make a blinking clock with a difference!

Updated 18/03/2013

Followers of my website would realise that I tend to make too many clocks in those tutorials. Well, I like making clocks… so here is another one. However this time I have tried to make the most simple version possible. Usually projects will have many LEDs, or perhaps an LCD, buzzers, buttons, all sorts of things. Which looks great and will impress many. But the other day I thought to myself … “how few things do you need to show the time?”

So here is my answer to that question: Blinky the one-eyed clock …

workingsss

It reminds me of the giant killer orb from The Prisoner… Using a minimal Arduino bootloader system, a DS1307 real time clock IC and an RGB diffused LED … we can make a clock that blinks the time, using the colours of the LED to note different numerical values. For example, if the time is 12:45, the clock will blink red 12 times, then show blue for a second (think of this as the colon on a digital clock) then blink four times in green (for forty minutes), then blink three times in red for the individual minutes. If there is a zero, blink blue quickly. Then the clock will not display anything for around forty seconds, then repeat the process. Here he (she, it?) is blinking the time:

Setting the clock is simple. It is set to start at 12:00 upon power up. So for the first use you have to wait until about five seconds before midday or midnight, then power it up. To save cost it doesn’t use a backup lithium battery on the real-time clock IC, but you could if you really wanted to. If you would like to follow my design process narrative, please read on. If you only want the sketch and schematic, 🙁 head to the bottom of this article.

Design process narrative…

So let’s get started!

The first thing to do was test the RGB LED for brightness levels, so I just connected it to the digital output pins of my Eleven via suitable current-limiting resistors. Each LED is going to be different, so to ensure maximum brightness without causing any damage you need to calculate the appropriate resistor values. This is quite easy, the formula is: resistor (ohms) = voltage drop / LED current So if you have a 5 V supply, and LED that needs only 2 volts, and draws 20 milliamps (0.2 amps) , the calculation will be: resistor = (5-2)/0.02 = 150 ohms. To be safe I used a 180 ohm resistor. The LED was tested with this simple sketch:

It was interesting to alter the value of d, the delay variable, to get an idea for an appropriate blinking speed. Originally the plan was to have the LED in a photo frame, but it was decided to mount a ping-pong ball over the LED for a retro-style look.  Here is a short video of the result of the test:

If you are going to use a ping-pong ball, please be careful when cutting into it with a knife, initially it may require a lot of force, but once the knife cuts through it does so very quickly:

cuttingppballss

Now it was time to develop the sketch to convert time into blinks. The sketch itself is quite simple. Read the hours and minutes from the DS1307 timer IC; convert the hours to 12 hour time; then blink an LED for the number of hours, display another colour for the colon; divide the minutes by ten and blink that in another colour; then the modulus of minutes and ten to find the individual minutes, and blink those out. Here is the first sketch I came up with. Finally, the code was tested using the Eleven board and my DS1307 real time clock shield. It is best to use existing hardware while testing, before committing to purchasing new hardware and so on. So here it is on the breadboard:

workingprototype1ss

And telling the time! In this example, the time is 3:45…

But perhaps that was a little bland. By using analogWrite() we can control the brightness of the LED segments. So now there are two more functions, whiteGlow() and blueGlow(); whose purpose is to make the display “glow” by increasing then decreasing the brightness. And scale back the amount of blinking, to increase battery life and make blinky less obvious. So now the display will glow white to announce the forthcoming display of time, wait a second, blink the time (with a blue glowing colon) then stay dark for ten seconds before repeating the process. Here is a quick demonstration of this display style:

Here is the sketch for the above demonstration, and the final one I will use with the hardware prototype. Once happy with the sketch, I put a fresh ATmega328 with Arduino bootloader in the board and programmed it with the blinky sketch, to be used in the final product.

Next was to build my own hardware. My last hardware unknown is the amount of current the circuit draws. Once I know this the correct voltage regulator and power supply can be decided upon. I had a fair idea it would be less than 100 milliamps, so I put a 6V battery onto supply duty via a 78L05 5V regulator (data sheet), and recorded the result:

So it varies, between 20.5 and 46 mA. As it only reaches 46 mA for a short time, we could consider the constant draw to be averaged out at 30 mA. I really want this to be able to run from a battery, but without having an external lead-acid battery lurking around, it will need a plug-pack with an output voltage greater than 7V DC. Another alternative would be to run it from a USB socket, a nice source of 5V. If doing so, there wouldn’t be a need for the 78L05 regulator. Which brings us to the  circuit diagram, which includes the power regulator:

blinkyschematicss

 

It does not allow for programming in the circuit, so you will need to program the microcontroller on another Arduino or compatible board, then transfer it to the blinky circuit board as described above. At this stage I tested it again, but using a solderless breadboard. In doing so you can make final hardware checks, and  generally make sure everything works as it should. This is also a good stage to double-check you are happy with the display behaviour, default time and so on.

breadboardedss

Time to solder up the circuit on some stripboard. Blank stripboard varies, but luckily I found this and a nice box to hold it in:

boxandpcbss

Stripboard does vary between retailers and so on, so you will need to work out the layout with your own board. In doing so, please double-check your work – follow the layout against the schematic and so on. Have a break, then check it again. There is nothing worse than soldering away to realise you are one strip too far over or something. My hand-eye coordination is not the best, therefore my soldering isn’t pretty, but it works:

solderedfrontss

 

solderedrearss

One would say that there is a good argument for making your own PCBs… and I would start to agree with that. The LED is soldered to some short leads to give it a bit of play, and some heatshrink over the legs to keep them isolated:

heatshrinkledss

 

And finally, to add a DC socket to feed blinky some power…

finalbaress

 

The last thing was to check the soldering once more under natural light, to check for bridges or shorts, then have a cup of tea. Upon my return I drilled out a hole in the enclosure lid for the LED, and one one the side for the DC socket, and fitted the lot together… and success! It worked 🙂

So there you have it. The journey from a daydream to a finished product… well a prototype anyway. But it works, and that is the best feeling of all. You can download the schematic from here. And here is the Arduino sketch:

I hope you enjoyed reading this post and hopefully felt inspired enough to make your own.

In the meanwhile have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, subscribe  for email updates or RSS using the links on the right-hand column? And join our friendly Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

Posted in arduino, clocks, ds1307, microcontrollers, projects, RGB LED, tutorialComments (18)

Let’s make another Arduino LCD shield

In this tutorial we make an LCD shield for using 20 character by four row LCD modules with Arduino Uno.

Updated 18/03/2013

In this article you can follow the process of making another LCD shield for the Arduino Uno or compatible boards. In the past (which explains the word another in this title) I made a 16 x 2 character LCD shield, however it was not backlit, nor large enough. Recently I acquired a 20 x 4 character backlit LCD for use in my Arduino tutorials, therein making this project necessary. To refresh your memories, here is the original shield:

p1070054small

However this time, I cannot mount the display on the shield, it is just too large. Furthermore, it is preferable to be able to stack other shields on top of the new LCD shield. Therefore the display will be external and connected with lengths of wire. So time to get cracking. The first step was to assemble all the parts together. The new LCD has a standard 16-pin  HD44780 interface, and is very easy to connect:

partssm

What we have: one 20×4 character backlit LCD, a Freetronics basic protoshield, some stacking pin headers, a button, 10k ohm trimpot for contrast adjustment, and some spacers and matching screws to give the LCD some legs. Afterwards I got some 0.1uF ceramic capacitors as well, to smooth supply current on the 5V rail of the shield. Here is the data sheet for the LCD: 2004 LCD.pdf.

As usual the first thing to do was to make a plan. The LCD interface is easy enough, but I still like to have something on paper to refer to:

schematic12

The next step is to breadboard it – to make sure it works. However I did solder in the wires to the LCD at this stage:

lcdwiressmall

And after assembling the circuit, a brief test:

testingsm

Success. The demonstration sketch is the example provided with the Arduino IDE, modified for a 20×04 LCD. During the test above, I used an external 5 V power supply for the breadboard. Remember to connect the ground line from the Arduino to the ground line of your breadboard, otherwise it will not work. At this point I was wondering how much current the LCD used by itself. The data sheet claimed it was five milliamps… I think not. Mr Multimeter had a different opinion:

ammetersm

Now it was time to finish the soldering work. Instead of trying to jam all the wires together along the digital pins, I used some wire jumpers to spread out the landing points for the wires from the LCD:

solder1s1

Furthermore, I decided to install a power LED and 560 ohm resistor – you can never have too many LEDs. 🙂 The rear of the protoshield was also quite neat, dollops of solder easily bridged pads when required. Then after a visual inspection it was time to solder in the header pins. The easiest way to do this is to use an existing shield:

solder2s

After soldering in the pins, the first attempt of using the display was unsuccessful. I had confused a couple of wires, but some reprogramming of the sketch fixed that. (It was Saturday night and my eyes were tired). But once the error had been fixed – success!

worldclocksm

If this shield/display needed a name, I would call it the Dog’s breakfast. Now, hardware is only half of the solution – there are one or two things to take into account when writing your sketch. Also, when using .setCursor(x,y); to position the cursor, the top left position on the LCD is 0,0; and the bottom right is 19,3. For example, the image below was created by:

abcdsm

Now to make something slightly more useful to take advantage of the screen area – another clock (I like clocks) using my DS1307 real time clock shield. Here is the sketch, (doesn’t allow for DST):

… and an action shot:

worldclocksm

So there you have it. Another way to use an LCD with an Arduino, and show how you can do things yourself. High resolution photos are available from flickr.

In the meanwhile have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, subscribe  for email updates or RSS using the links on the right-hand column? And join our friendly Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

Posted in arduino, HD44780, LCD, projects, tronixstuff, tutorialComments (3)


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