Friday, February 19, 2010

Chapter 4 - Exercise 18 Almost Done

So I finished wiring up the other two 4026 chips... still careful about grounding myself before touching them.

As you can see from the pictures, my breadboard isn't nearly as pretty as the author's version (see page 178). Doing this exercise really makes you appreciate the author's hard work with trimming all those wires to make it look pretty - and trimming... and trimming... and cutting... and trimming.

On the positive side, I'm done with most of the wiring... on the negative side (get it - positive, negative) I'm almost out of green wire! Next time I visit ACK I'm going to invest in blue, yellow, and any other colors they may have... red, black, and green are fine, but I wouldn't have minded wiring up the 2nd 4026 chip with yellow and the third 4026 with blue... just to keep everything easy to find.

Anyway, here's a video showing the circuit working... press S3 and it zeroes out the LED. Press S2, and it increments by 1 (most of the time)... holding down S1 locks the LED and any further presses of S2 while holding down s1 don't add to the increment.

One somewhat tricky part of the schematic on page 174 (Figure 4-37) is the jumping of pin 15 on all three 4026 chips and then throwing in a 1k resistor and pushbutton (for S2). I did it on the first try, but you really have to examine the schematics to see how best to make things work.

I'm almost done - now I need to wire in some 555 timer chips and some capacitors to create the reflex tester game. When done, I'll have completed 50% of the book's experiments. Have a great weekend, everyone!


  1. It worked! Well, that's a relief!

    Congrats, James. The projects get easier from this point on (I think).

    Incidentally, neater wiring is easier when you use thinner wire. Looks to me like you used 20 gauge. In any future edition I think I will recommend 22 gauge. Stripping the insulation is a little more difficult, but manipulating it is easier.

  2. Thanks, Charles - I was very happy to see it work, too.

    As for wire - all the wire in that circuit is 22 gauge solid core. It inserts into the breadboard easily and can be molded. I just didn't do as good a job with the presentation :)

    Question: When I powered up the circuit, the LED display 009 and sometimes 005 but never 000 or any other numerals for the 3rd digit... any idea? Once I hit S3, it zeroed out and all digits displayed fine... it's just weird that powering it up seems to have some sort of effect on the initial LED display.

  3. I can't remember the factors affecting the initial state of the counters. My guess is that the registers inside the counters have an arbitrary initial state relating to small manufacturing variations. You could try swapping two of the counters, see what happens.

    The circuit badly needs an initializing routine. I think I mentioned this in the book. I just didn't want to make it any more complicated, and in any case, I had run out of room on the breadboard. But ideally you would have another 555 timer that would send a pulse to the counter reset pins...something like that...and that would be its only function.

  4. Finished this one this morning. Was running short on wire when I realized I had a roll of 4 conductor telephone wire on the shelf. The 24 awg solid wire fit nicely in the breadboard and allowed me to dedicate a different color to each counter and its respective digit.

    I had one bad 4026 counter that wouldn't reset its assigned digit when powered high. Glad that Component Pack 2 contained an extra, though I wonder that the 4026s weren't shipped in conductive foam given the warnings in the book about fragile CMOS chips.

    My frustration however is with capacitors. When I started the book I bought several bags of assorted ceramic and electrolytic capacitors figuring that surely they would contain the ones I needed, but I continue to come up short of the ones most needed for these projects.

    I do wish the book contained a section on how to read the markings on capacitors. The electrolytics are marked clearly enough, but the ceramics and the tantalums give me fits, especially since my eyes are getting old, and I seem to have an inordinate amount of difficulty getting the decimal point in the right place when changing from micro to nano to picofarads.

  5. Jim, thanks for blogging this. I've been working through the book and just found your site. It is great to have some folks to walk through this with, albeit a year later.

    I just finished this circuit, everything works fine now. My problem has been that I was relying too heavily on salvaged parts. I was not aware of common anode (CA) and common cathode (CC) seven segment displays. Now I know. Once I sorted that out and actually bought the correct part I was fine. Thanks again.