Thursday, February 18, 2010

Chapter 4 - Exercise 18 Debugging

I'm uploading a few closeup shots here of my circuit as I've assembled it. Ignore the color of the red and black wires I'm using to connect the top of my breadboard to the lower part. I haven't yet purchased blue and red Sharpie pens to color code the columns but if you're looking at the photos, the right-most column is positive voltage and the left-most column is negative voltage. I've also used wires to mimic the setup you see in Figure 4-34 so I can have a positive column running down the 2nd from the left side and a negative column running 2nd from the right.

I've also used my multimeter to check the 9V on the 100 microfarad capacitor at the top of my breadboard AND along the bottom - voltage is consistent across the entire breadboard. I also tested my LED again before rebuilding this circuit and all the segments that should light up are working.

At this point, the circuit is still not working. I substituted a 2nd 4026 chip and no luck. According to ACK Supply where I purchased these chips, they are Thomson Consumer Electronics chips - part # "CD4026BE RCA" - I wasn't able to find a data sheet on this particular chip with the Thomson name, but I did find this one from Texas Instruments. I'm assuming here (maybe incorrectly) that all 4026 chips are supposed to have an identical pin layout... but since I can't find one specific to Thomson chips, this may very well be my problem... but I'm guessing that it wouldn't make sense for different chip makers to switch around the pins. Again, maybe I'm wrong.

If you see a wiring problem, let me know... I used black wires to connect the 4026 chip to the negative voltage and red wires for positive. Green wires are used to connect all the other pins to the LED with the exception of pin 9 where I used a black jumper wire. I'm really hoping this is user error and that I'm just being blind to something really really simple... otherwise, I'm going to have to go and purchase additional chips from a different maker just to rule out bad chips or bad pin layouts.

For right now, I'm stuck...


  1. Have you tried moving the circuit to a different part of the board? Maybe there is a broken connection in the bread board somewhere. Or maybe you can use the multimeter to make sure all of the points are receiving current.

  2. James, you do not show the top of the breadboard, but I am assuming you are supplying positive and negative down the pair of left-hand buses, and also positive and negative down the pair of right-hand buses.

    Unfortunately you have only jumpered one of the pair of buses on the left, and one of the pair of buses on the right, to connect power to the bottom half of the breadboard. Therefore your pushbutton is not receiving any power, and your counter chip also isn't receiving all the power that it should have. Add the missing jumpers to connect both of the buses on each side, and you should find a marked improvement.

  3. If there is a second edition of the book, I may include an advisory specifically warning people not to buy breadboards where the power buses have a break midway. This already gave you grief in a previous experiment, and it has caught me out too, in the past. The idea is that you can apply a different voltage to the bottom half of the board, but that creates its own opportunities for error. I really think it's a bad design.

  4. AHHHHH! Charles! I'm running up now to test that! I cannot BELIEVE I made that kind of serious goof! ARGH ARGH ARGH!

  5. I'd also suggest always wiring with 3 wire colors:

    Red == Always Vcc -> Circuit
    Black == Always Circuit -> Ground
    Green == connections within the circuit that are between components, but not directly to Vcc or Ground.

    This sort of convention, even though it can be a hassle to cut wires to the right lengths when you need them, will also go a long ways towards preventing fried LEDs, capacitors, etc.

  6. The nice thing is, you'll never forget it now. I had a chip the wrong way around in a breadboard once. I had left it in so long, that when I went to pull it out, it had gotten so hot that I burnt my finger.

    Lesson learnt and it's now the 1st thing I check every single time :)

    I'll echo, red:+ve, black:-ve and any other colours for everything else