In this part of the series we’ll cover the electronics. I’ll show you how I planned to build the internals of the clock and how I built it afterwards. Just like in the first part of the series I wrote this article while the build was in progress. I planned to leave errors I might make during this build in the articles, so that me and others can review them and don’t make the same mistakes again. If I find out that something is wrong, I’m going to mark it as wrong in the article and correct it afterwards:
mistake I made
However in the last part we planned our clock in general. So now it’s on to planning the electronics that’ll give the clock a function.
Choosing the right parts
We’ll obviously need some LEDs to light up the letters that display the time, so We’ll start here. This depends on how many rows and columns your design has. Mine has 12 x 12 = 144 letters in total. So I’ll need 144 LEDs. You can basically choose any ‘conventional’ LEDs you want (You’ll see in a second why it doesn’t matter a lot). Any 5mm through-hole LEDs should do the job just fine if you don’t know how (or simply don’t want) to deal with SMD-LEDs. Just make sure they are bright enough. The colour basically doesn’t matter that much either. Just choose anything you like. However I’d suggest bright colours like white, yellow or light blue. Dark blue just wouldn’t look right in my opinion. However it’s a DIY project, so just go for it if you like it!
I drilled 144 holes with a diameter of 5mm each (You could also drill 288 holes for the little legs of the LEDs). Yes, it was as frustrating as it sounds like. So after I did this, I mounted 144 RGB-LEDs in the holes, each in the same direction. Afterwards I started to solder together the corresponding pins on the LEDs. Each column and each row has to be connected either on the anode or the cathode, depending on what kind of system you want to build.
I have to admit that after two hours I gave up and made a PCB design instead. However it’s the first revision and I have to say that it’s not that well made, but it should work. It was more or less just a quick design I made in under an hour. I’m currently working on a nicer and easier to manufacture/build revision. I’ll post updates here. I actually can’t guarantee you at this moment, because I’m also just building it and I will continue the build next week, because I’m still missing parts of my order.
However the design consists of three separate PCBs and each of them is 260 by 90 mm large. Basically it’s three times the same PCB. Each board has one MAX7219 LED-Matrix driver on it, that controls 48 individual LEDs. You could basically manufacture one board that is 260x270mm large, but it’s easier to make three separate ones and daisy chain them together. This way you could create (almost) whatever size of clock or Panel you want.
I want to control the chips with an Arduino Nano. I’m going to talk about this aspect in the Software-part of this series.
However, you can download the design here.
The package itself contains a high-res printable PDF-File, if you want to manufacture the PCBs yourself, and all the eagle design files for you to change/review or for manufacturing. If you redistribute the package please leave the original text on the PCB design intact or supply a link to this page. Thanks!
As requested in the comments, here are some pictures that show how my PCBs turned out. You don’t have to worry too much. The details look tiny on the image but the PCBs can easily be etched!
The PCB design got updated! You can read all about revision B here!
Complete list of parts
Okay so if you want to build the electronics this way, here are the parts I used. You might want to consider using stronger LEDs or switch the package in the PCB design, because the ones that I intended to buy are not manufactured anymore and other ones are quite expensive and not as bright. However here is my list:
Broadcom PLCC2 Amber SMD-LED Link
|Quantity / Total price||Part||Supplier|
|150 / 28€||Broadcom PLCC2 SMD-LEDs (Amber)||Link|
|5 / 0,70€||Panasonic electrolytic capacitor (10µF)||Link|
|5 / 0,75€||WE electrolytic capacitor (0.1µF)||Link|
|5 / 0,80€||1000 Ohm resistor||Link|
|5 / 2,20€||eCon IC-Socket 24 Pin-DIP||Link|
|10 / 0,80€||5-Pin header||Link|
|2 / 17,78€||PCB-material||Link|
Just a quick note: The PCB-material is 1-2€ cheaper at reichelt.
The LED-matrix control IC is not on this list, because I found it to be hard to get at a reasonable price. However from time to time you can find LED matrix kits on ebay/amazon where most of the time a MAX7219 is used. I bought 5 kits, named “MAX7219 Dot matrix module MCU control Display module DIY kit for Arduino” for 15€ total. You might need to look around a bit until you find a reasonable price.
You’ll also need some kind of time keeper, as the arduino is not capable of properly doing so itself. I ordered this RTC module, but anything with similar functionalities should work fine.
Update 29th of April, 2017
Currently I can recommend this auction on eBay. You can get them very cheap for 1,50€ per kit and you can use the kits to control the matrix board later, without having to craft an extra daughterboard!
Table of contents
Part 1 – First steps
Part 2 – The Electronics (You are here)
Part 2.1 – Quick update and Board Rev. B
Part 3 – The Software
Part 3.1 – Updated Revision
Part 4 – Completing the build (Not released yet)