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4 bit Adder - Construction & Testing

My first build of this circuit was on a breadboard to see if it worked. As I hadn't ever breadboarded anything before I planned it out, but really this was a stage I could have skipped given the basic design of the circuit. Here's the layout that I came up with:

(click to enlarge)

And here it is built. If you look carefully you might be able to see that some of the pull up resistors are missing as I ran out of components. Electronics is expensive you know! :D. The odd breadboards are also a reflection of what I had to hand, hence using two small ones rather than one large one.

(click to enlarge)

Once I was satisfied that the design worked, I then decided to make a more permanent version. I invested in a Weller WHS 40D solder station after reading/watching some guides on what to buy (and what not to buy). This EEV blog video was especially helpful (many thanks Dave!). Also purchased some 60/40 lead-free 0.5mm solder and the components for the project.

My soldering skills have never been great - in fact they've been awful in the past - so Iwas a little nervous of soldering my project together. However, after watching the above EEV blog video and using my new Weller solder station suddenly my soldering looked a lot better (although still not great - but things have gotten better since). Goes to show that buying deceent tools and looking up the basics can make a huge difference.

Here's the final result (top side to the left, underside to the right):

(click to enlarge)
(click to enlarge)

Now, in some places it may look as if there is too much solder. This is due to my choice of trackless perfboard and me trying to link pads together by using solder alone. Since this project I still use the same perfboard (I just don't get on with the tracked type), but I will now tend to use cut off component legs to link pads side-by-side rather than only groups of 3 or 4 or more.
I also tend to use 30AWG wire-wrap (Kynar) wire as well, rather than the thicker 22AWG stuff I used here.

Speaking of the wires, the colour coding is:

Colour Connection
Blue SW1 to Adder inputs
Orange SW2 to Adder inputs
Green Adder ouput to LEDs
Red +5V rail
Black Ground / 0V

On the component (top) side you can see that I used a DIP socket for the Adder IC. This is so that I could safely solder that in without the heat from the soldeirng iron damaging the IC itself. Also, removal is much easier in the event of a faulty component or if I ever need to borrow the IC for something else.

One slight flaw that I spotted whilst typing this page was that the 100nF smoothing capacitor next to the Adder IC has it's ground leg connected via a long circuitous route to the 0V rail. Ideally, this should be connected as close to the VDD/VCC and GND pins of the IC as possible. With a project as small as this with only one IC it's not a major issue, but for larger projects with multiple ICs it becomes more important.

Well, that's about it. As minor and less-than useful as this circuit is, it gave me a great sense of satisfaction designing & making it and it taught me quite a lot.

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