Sunday, January 31, 2010

Chapter 3 - Exercise 14 Part 1

I'm breaking the post for Exercise 14 into two posts. For this first part, I've breadboarded the circuits found on page 118 (Figures 3-75 and 3-76). I initially tried to substitute the 220 microfarad capacitor for C1 because I didn't have a 100 microfarad capacitor... the LED just stayed lit... no blinking. So, yesterday while I was out running errands, I swung in and picked up a few things from Radio Shack. More on that later.

This is the first time we're given a schematic without a matching breadboard drawing - I tried to build the circuit without glancing back to page 85 for help... my first attempt worked, but even with the proper 100 microfarad capacitor, the LED stayed lit... so I knew something was wrong. After checking my circuit again, I found I'd made a few connections wrong with the 2N6027. A quick glance back to page 85 also helped me make sure I'd wired it up correctly. I highly encourage you to try and wire it up without looking at page 85... but if you get stuck, the photo to the left is a closeup of my circuit that works.

After testing that circuit, I moved on to Figure 3-76 and added in C2 and the 330 ohm resistor. I got it correct on the first try... again, try to do this yourself... but if you get stuck, my photo shows a closeup of the breadboard layout that I used successfully.

I'm including two videos here - the first shows the single C1 circuit... the second shows the circuit with C1 and C2. The red LED pulses nicely. After reading ahead in Exercise 14, I found the author is suggesting mounting the LED in some acrylic to make it all look pretty. I think I'm going to try something different... let me explain.

I switched the voltage from 9V to 6V because I found two small watch battery holders (solderable) at Radio Shack for $0.99 each... I also purchased a small project box and a perf board that can be broken in half - one half will fit nicely in the box after I trim the edges a bit. Doing this will also require that I rearrange the layout of the components found in Figure 3-79. I'm okay with that, and I think Mr. Platt would be, too. We're supposed to be experimenting and trying new things, right? I'm including a photo here of the parts - and I'll also provide a parts list and pricing below. No guarantee it'll work, but it should be fun to try.

Up next, I'm going to start the soldering... as you can see, my soldering will differ a bit from Figure 3-79 but I'll try and do my best to photo and explain my layout in the next post.

Coin battery holder CR2032 - Part 270-009 $0.99 each
220 microfarad - Part 272-1029 $1.29
100 microfarad - Part 272-1028 $1.29
PC Board - Part 276-150 $1.99
Project Box Small - Part 270-1801 $2.29

I hope everyone had a great weekend!


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  3. I set up the circuit just like you did based on pg 85 and I could only get the first one to work when I removed R4. For the second circuit I could only get the LED to light up and stay lit. I have my circuit set up the same way you have in you pictures, do you know what might be wrong?

  4. Not sure, Mike... I think it took a couple of tries before I got the circuit to work - this really involved going back over and over and rechecking all the connections.

    For a circuit this simple, my best is guess is one of two things:

    1 - error on your part (more likely, trust me... and I've made tons of errors working through this book)

    2 - a bad components - substitute one item at a time to check the circuit.

    My guess is that it's something fairly simple... good luck, and let us know if you find the error and what it was.


  5. I have the Make Component Packs 1 and 2, and there was a little gap in coverage for this specific experiment-- neither kit has the 330 ohm resistor or the two capacitors (100uF and 220uF). Further, Pack 2(likely accidentally) included two male header strips and no female strips.

    No biggie -- all the above was under $10 from Radio Shack, and at this point the boy and I should begin building fluency in buying specific parts from our local RS. The closest thing they had to the header strips are called 'PC Board Terminals', part 276-1388.

  6. I've had the same problem with the circuit in fig 3-76 as Mike did above. The LED has an initial flash and just stays on when I am using 9V. When I use 6V (or even 7.5V) the LED blinks just fine, and it isn't dim either. So there's something about the 9v it doesn't like.