Thursday, October 7, 2010

Chapter 5 - Exercise 32 Debugging

Suggestions are coming in on ways to test or fix the problems I'm encountering. Let me explain what's happening now.

I've inserted the diode that j suggested... works! The buzzing has disappeared (see video below). So we're getting close. Right now, pushing either switch (that will serve the robot as a trigger to stop and back away from an obstacle) does not stop the motor from spinning - pushing either button is SUPPOSED to cause a drop in voltage on pin 2, so I think my next step is to use a chip tester to see if pin 2 is being triggered. (Right? No?)

I'm including some pictures here - one is the schematic and the rest are close-up photos of my circuit - maybe I've got an unseen error in my wiring. Be warned - my use of the breadboard is obviously that of a newbie, so I've got wires running all over the place. If I can't figure this out soon, I think I'll start over and try to rewire a bit cleaner and closer to the layout of the schematic.

Thanks in advance for all your comments and suggestions - I love learning by doing... and making mistakes is another favorite technique of mine as I tend to remember what I did wrong versus what I did right... and that's what drew me to this book in the first place!

First video below is WITHOUT the diode.

Second video is WITH the diode.

(FYI - family visiting this weekend so I may not get much more work done on this circuit until early next week.)


  1. It's hard to tell from the photos whether all the wiring is correct but I think you have a definite problem with the relay wiring.

    You appear to have the motor connected between pins 6&11 instead of 4&13 (& vice versa)
    See for numbering.

    If you add the diode it should be connected across the coil (Pins 1&13) and not in-line with the connection to IC1 pin3. Looking at the picture it doesn't appear connected anyway as it is shown connected to the non-existent pin 15.

  2. ... *cough* obviously I meant pins 1 & *16* for the coil.

    See for an explanation of why the diode might be used and which way round it should be connected.

  3. After looking at that Twitpic, I think you're totally correct about my wiring of the relay - will take a look at that shortly. Thank you!

  4. Ooops again.
    I changed my original picture to reduce the amount of rework you needed to do but this would actually result in the motor running in reverse until a microswitch is activated. For numbering that actually matches the circuit see the picture at

  5. As an afterthought. While the motor direction may not matter in a tabletop exercise if you planned using it in a real robot situation you might prefer to choose the option where the coil is not energised by default. Thereby reducing power consumption by that last little bit.

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