Tuesday, February 9, 2010

Chapter 3 - Exercise 15 Completed

A short post and summary today - I've got myself a cold and am not feeling so well.

I got the project box completed - soldered up all the LEDs, button, switches, speaker, etc. I left the power jack on the bottom unfinished... since I don't have a 12V power supply to spare, I'm not sure if I'll complete that part of the project any time soon.

A few notes about the project box - I had to redrill the four holes in the circuit board to mount them to the box - I used a 1/8" bit to enlarge the holes and I purchased 4 #6 bolts to fit in the four holes I drilled in the back of the box. I bought 4 small nylon nuts (#8s) to serve as little posts for the circuit board to sit on... works fine.

The project works... sort of. The green LED does not light up to test the circuit - either I burned it out (I did use a copper clip) or soldered something incorrectly, but I just can't get that part of the circuit to work. The box does work, however. When I have the magnetic switch closed (see video), I can flip the power switch - the red LED lights up. When I break the magnetic switch, off goes the alarm.

I'm ready to move forward (once I get to feeling better) and away from the exercise, so I'm going to put this aside for now and maybe come back to it in the future to try and figure it out. For now, I've learned what I can from this exercise and am looking forward to Chapter 4 that starts us on Integrated Circuits... woo hoo!


  1. I've just completed exercise 15 to this point as well, and guess what? My green LED won't light up either. Everything else works as expected, but no green light.

    In assembling the project, I ran into a run of bad 2.2 mFD capacitors, which make my circuit board look awful now that I have pulled out and replaced them. I also fried one of my PUTs in the process of switching out the caps. A loss since they are getting quite difficult to find.

    Lesson learned...from now on I will leave the assembled project on the bread board so I can test each component in a fully operational circuit as I add it to a more permanent substrate.

    I rearranged the final circuit board for a more compact arrangement, anticipating that I would need room for future modifications.

    I arranged the front panel with room for the keypad so that once I finish experiment 20, I can, hopefully, adapt the switching circuit to control the alarm.

    We are wiring the sensors into my eight year old's bedroom so he can "little sister proof" it. Of course, that means I will eventually have to build a duplicate for his little sister too.

    I added an internal power supply in the form of an old, but healthy NiMH battery that I no longer use in model airplanes. Once I learn a bit more about regulating power, I will construct an external power supply that delivers a very low current trickle charge, although with an 1100mAH battery, I think probably the system won't need a charge all that often. I'm thinking that a power meter of some sort might be cool...or maybe a simple LED blinky when the voltage drops below a set level.

    Anyway, I am enjoying your blog and also enjoying working through Mr. Platt's book.



  2. I couldn't leave it alone. I woke up around 3:00 AM remembering that I had cut a jumper wire to run from the power switch to the test switch for the sensor network, but couldn't remember soldering it in.

    Out to the shop in my pajamas, I opened up the box and found that indeed I had left out the wire. Soldered it in and found that the green led glowed merrily when I pressed the test switch. Then I managed to set off the alarm and wake up the whole house. Oh well. Edison's family had to make sacrifices too.



  3. Still fussing with this project. The alarm is intermittent. Sometimes it begins wailing as expected when the sensor circuit is broken. Other times the hi frequency oscillator begins to wail until the low frequency capacitor charges, then the high frequency cuts out and there is a low frequency click..click..click.

  4. Yeah, I still remember having issues with this one. I think the key to this and every exercise is knowing when it's time to move on... I think as long as you understand WHAT you're supposed to take from the lesson, you've succeeded.

  5. Agreed. Still, it's rather unsatisfying as an alarm if it doesn't reliably wail.

    The 555 timer awaits my attention however...

    Just ordered your CNC book by the way. Hoping I can fit it into the space where my router table currently resides.

  6. I hope you enjoy the CNC book - I can't tell you how much fun it is to have a working CNC machine in your own garage (or workshop). Let me know if you have any questions, and do check the book's forum discussion area as a few errors have been found (and corrected) by readers. I've had about a dozen people tell me they built the machine directly from the book, however.