Thursday, January 21, 2010

Chapter 2 - Exercise 11 Step 2

This post covers Step 2 (of 4) for Exercise 11.

Step 2 will have you adding some more components to the circuit you built in Step 1. You're also asked to add an 8 ohm speaker to the mix. I built the circuit as shown on page 86, but was unable to get any sound coming from the speaker. I checked and double-checked my wiring, but no buzzing sound... so...

I removed the speaker, added in a white LED (removed R7) and basically built the same circuit found in Step 1. As you can see from my photos, the LED stays lit... and the original circuit (green LED) blinks slowly enough I couldn't get a picture of it flashing... but it did flash at its normal speed. The white LED, as expected, stayed continually lit.

So, I removed the white LED, put the speaker back in (for a photo) and tried to listen for a buzz... but nothing. Either my hearing isn't that great or this little speaker just isn't putting out that much noise. We'll find out tomorrow, because apparently we're going to be amplifying the speaker in Step 3... if that doesn't work, I may have a busted speaker.

A few notes about this exercise:

1. My first try at powering up everything, including the white LED failed... then I remembered. Duh. I needed two small wires to link up the top half of my breadboard with the lower half. Apparently my breadboard's positive and negative voltage columns do not run top to bottom completely... so I stripped off the ends of two small wires (one red, one black) and connected them as you can see in the pictures.

2. I believe I've found an error on page 86 - the speaker's negative terminal wire is shown plugged into the negative voltage column's left-most column... should be the right-most column where R6 and C2 are connected. I tried it both ways (hey, who knows... maybe it's correct, right?) but no luck. I'm fairly convinced it should be tied into the circuit by plugging the speaker's wire into that right-most column.

3. If you don't have a .0047 microfarad capacitor, you'll need one for this exercise. You'll also need two of the 2N6027 PUTs... if you've only got one, you won't be able to finish Parts 2, 3, or 4.


  1. James is correct about the error in the diagram on page 86. But if the speaker wire is connected to the negative source, it should work. You could actually try connecting it to positive, so that Q2 sinks current instead of sourcing it ... this is just a guess, though. Also try the paper-tube trick shown on page 87, which multiplies the volume a lot. If you still can't get it to work, maybe I'll rebuild this little circuit myself just to make sure.


  2. You could also measure the resistance of the speaker with your DMM to make sure it reads around 8ohms. It could be shorted (0 ohms) or "open" (infinite ohms).

    My personal favorite car audio installation speaker trick is to just momentarily tap the speaker wires to a partially dead 9v battery and see if it makes a pop sound. This is particullary useful when you have 4 pairs of wires and no idea which is (front|rear) & (left|right).

  3. There are a couple other exercises before this one where he has them plugged in that way, too. Hopefully they get that sorted out.

  4. Nick,

    Seriously? Where? I've tried my best to watch for this kind of thing, and Charles Platt is wanting errors to be pointed out so they can be fixed in a later edition.

    If you or anyone else find errors, please submit them to O'Reilly or add a comment here.

  5. Yea I ran into the same thing, the diagram in the next part of the experiment also shows it plugged into the left column. But the PHOTO shows it on the right column. When I did as the photo showed, all worked fine.

  6. Ian,

    You're talking about the jumper wire, not the speaker, right? I can see the jumper wire isn't is in the wrong column on the right side... minor bug but could stump someone who hasn't quite caught onto the breadboarding concept and follows the images exactly.

  7. BTW,

    Charles Platt has emailed me and asked for errors to be forwarded to him, so don't worry about speaking up - point out errors if you find them... even if you're not certain. We can help him improve the book and help one another get the most from the book.



  8. Hmm, no, actually I think it was the speaker wire that was in the wrong column. Unless I messed up another part of the circuit, but that somehow fixed it?

  9. Yes okay, we are on the same page. I looked at your photo and you have it the same way I eventually wired it, after I realized the wiring diagram must be wrong.

  10. Sorry... my confusion. In your first comment you said "the diagram in the next part of the experiment" which I took to mean Part 3 - and that has an error, too, which I didn't catch until your comment made me look. But you, too, were talking about the figure on page 86 for part 2... so yes, we're talking about the same diagram.

    And now, for Part 3, the diagrams on pages 88 and 89 both show a single jumper wire (in lower right corner) that needs to be connected to the far-right column.

  11. And for Part 4, the same jumper wire needs to be terminated to the far-right column. I'll try to remind everyone of this in my Part 3 and Part 4 write-ups.

  12. It's my first comment and I want to thank you for sharing your experience. It's been very helpful.

    I think I've found another error on the book. The capacitor used here is 0.0047 micro farad (uF), which should be 4.7 nano farad (nF), but on both page 43 the shopping list, and page 86 the description, it's said to be 47 nF. Seeing this, I made yet another mistake to buy a 47 pF capacitor, which didn't generate any sound. Now I'm using the 4.7 nF one and it all works well. So I don't know if the 47 nF capacitor will actually work but this is a mistake for sure.