I have been seeing these "Word Clocks" all over the internet for the past few years, but they never really impressed me much. Mostly because there is nothing special about them (from the electronics point of view) but after seeing QlockTwo made by Biegert&Funk I simply couldn't resist making one that looks that nice. But of course, in my local language. Aside from different language, I wanted it to be able to display full time - every minute of an hour - so I ended up using 248 white LEDs. To keep that stealthy look I used two capacitive touch sensors under the glass (near left and right LED dots) as buttons for the user-input.
UPDATE: There is a discussion about constructing the clock of the forum here!
The project is open source and you can download all files by clicking on red download button just under the article. Note: to "translate" the clock into other languages, you will need to make a front vinyl foil with your own word/letter combinations and to edit the language header file in the source code.
1. time display, obviously 2. date display 3. temperature display 4. seconds display 5. configurable times of showing for all of the above (for example, the clock can display time for 20 seconds, and move to next thing to display: date, temperature or both and go back to time. It can even be set to display only the temperature) 6. automatic LED brightness adjustment according to ambient light (with automatic sensor calibration) 7. corner LEDs (dots) blinking at 1/2 Hz rate (or even turned off) 8. sleep mode - shutdown until next button (sensor) press
Structure The build itself was a real motivational rollercoaster mainly because it involved gluing a "letter mask foil" with all the letters which was the most nerve consuming process, a lot of woodwork, lots of soldering and some programming.
The clock is made from 5 layers: a) Glass, b) Vinyl graphics, c) Tracing paper, d) Wood, e) Back side. Layers "a+b" are called The Front, "c" is just a paper to diffuse LED light, "d" is The Middle, and layer "e" is The Back.
The Front (glass + vinyl graphics) To make the front for the clock I decided to use 3mm glass with machine-polished edges in so called "flat polish" which leaves a nice small bevel. Glass is more scratch resistant, durable and cheaper then plexiglass so that's why I have chosen it. The foil with letters is a self-adhesive black glossy foil by SERILUX™ which was cut by vinyl graphics cutter machine. The idea was to glue it to the back of the glass (for that extra glossy finish), so it was very important not to "trap" any dust particles between the glass and the foil since it would ruin the entire look. The best way to do it is under the water, and if some dust falls on to our working surface it would stay on top of the water. Much easier way is to simply use a spray filled with water and just a drop of dishwashing liquid/soap. This solution is sprayed on the glass and on the sticky side of the vinyl during positioning on the glass. The water+soapy solution will lubricate the entire process and make it possible to re-position the vinyl even after the sticky side touches the glass. The water is then carefully squeezed out with a credit card.
Pool of water for underwater vinyl gluing - the unconventional way
Underwater vinyl gluing - the unconventional way
The process/tutorial of attaching vinyl graphics to the glass can be found all over the internet so I will not be explaining it here in detail, I will just say it is a two-man job for graphics of this size (17.7 x 17.7 inches). Foil graphics/letters are created and arranged using Inkscape - an open-source vector graphics editor. Font used is identical to the one used in QlockTwo - "DIN".
Vinyl graphics attached to the glass - currently incomplete letters
The Front is glued to the wood permanently by using transparent silicone. When cured, silicone can hold heavy loads and is usually used to attach glass to glass or other materials. I used small amount of silicone in case I ever need to remove it from the wood, but hopefully that will never happen.
The Middle (wood) Entire clock electronics are embedded in standard 18mm thick MDF wooden panel with edges banded with glossy white PVC band. I simply ordered 17.7x17.7 inches MDF board with glossy white PVC edges from the local kitchen cabinet manufacturer. After it arrived I had to make 248 cone-shaped holes and spray them with reflective paint, which took me few days do complete.
Widening the holes at the top... I didn't have the cone-shaped drill bit at the moment
Next step was to make the grooves in the wood for the electronics, PCBs with LEDs, all the wiring, and capacitive sensor PCBs on the front.
Making grooves on the other side
Grooves for electronics and holes for dots - done
Painting LED holes with reflective paint
Painted edges in black because the vinyl sticker was smaller than glass by 1mm, so "white" was visible
There is also a small 5mm hole through the PVC band in the bottom of the clock for the CdS light sensor.
Electronics The whole thing is a dot-matrix display with 244 LEDs and 4 corner LEDs. Microcontroller used in this project is ATmega328P but the code can fit into ATmega168P just as well. Time keeping is done by DS3231 (or DS3232) i2c RTC IC from Maxim. It is a very good and accurate IC that also has a temperature sensor inside so we can read the temperature from it too. There is no power supply regulator in the electronics because I wanted to avoid any unnecessary heating. There is just one 5.1V Zener diode for over-voltage protection. Everything is powered from a 220V/5V 1A "wall wart" SMPS AC adapter and I strongly rely on it's voltage output accuracy.
Main board schematics - click to enlarge
Main PCB drilling
Main PCB completed, still dirty
Main PCB done - soldered on top side as SMD components
Controlling all those 248 LEDs is done with four daisy-chained MAX7219 ICs. These ICs can control 64 LEDs each so I needed 4 of them for the entire display. The display is divided into 4 parts, one for each MAX7219 used.
LED matrix - the clock consists of four of these matrixes, one for each MAX7219
The PCB that holds LEDs - there are 56 of these in total
All 56 LED strips with LEDs soldered - placed into their groove
Now it is ime to connect the MAX7219 breakout boards
LEDs used in the project are SMD White PLCC-2 LEDs (eBay) that require just around 4-5mA each for total brightness. Since LEDs are multiplexed by MAX7219, the worst case scenario of current consumption is around 8*4*5mA = 160mA + few mA for the Atmel and surrounding ICs. In normal operation mode the entire clock consumes only ~40mA!
MAX7219 breakout board schematics - click to enlarge
MAX7219 PCBs soldered - 4 required for this project
MAX7219 PCB in its groove - time to solder them to LED matrices
All four MAX7219 PCBs soldered to their matrices
Later I added four corner dots. They are connected to two upper MAX7219 ICs since there are two unused LED rows for each upper IC
Just a note for soldering the LED matrices to MAX7219 ICs - no matter how you solder/arrange them, you can re-map them in the source-code. For example, if you mix Dig0 with Dig5 it is not a problem - there is a part of source code where you can change these references. I had to make that part of code because I freestyle-soldered these also. For user input I didn't want to put simple push-buttons simply because there is nothing special about them, so I ended up using two Atmel AT42QT1011 capacitive touch sensors which work excellent through vinyl+glass.
AT42QT1011 touch sensor schematics - click to enlarge
Capacitive touch sensor PCBs
Capacitive touch sensors soldered - AT42QT1011
Capacitive touch sensor panel - a piece of PCB, sprayed with PLASTIK 70 to prevent oxidation
Capacitive touch sensor panel - PCB will rest in it's groove
Touch sensor PCB in place
All parts are connected with wires like in the picture bellow, and power cable is the only thing left unconnected.
Main PCB connected to everything else
The Back (hardboard) The back cover is made from Hardboard, a 3mm thick wooden material 17.7x17.7 inches in size. I will probably leave the clock without it, maybe I will just put a white glossy vinyl instead, just to protect everything from dust coming in.
Testing the LEDs From all 248 LEDs I found that only one of them didn't actually work, three were badly soldered - oops!
LED matrix test
Images of completed clock
Videos of clock working
Normal clock operation, with date and temperature request
Clicking through the menu, turning off corner dots blink
Testing the automatic brightness and re-calibrating the CdS sensor
Videos made during development There are several videos I made during the development.
Display matrix test with one really BAD led
Since we have a dot matrix display, we can print text on it
Now all that is left to do, is to hang it on the wall permanently.
I know, but these LEDs that I have light up at 90 percent brightness with only ~5mA. The rest
~15mA will give them full brightness. Anyway, now I have changed the resistor for 20mA from the
MAX7219 datasheet - there is a table for your reference. IP: n/a
would like to ask how u choose Rset resistor for Max7219? And how is that possible that LED
needs just 5mA? Mine i got (1210 PLCC2) needs 20mA.
So the worst case scenario is 640mA for LEDS.. IP: 18.104.22.168