Urgh ... Homework project maybe?

Discussion in 'General Electronics Chat' started by SlowCoder, Apr 2, 2012.

  1. SlowCoder

    Thread Starter New Member

    Mar 25, 2012
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    Ok, so I'm currently stuck reading my Radio Shack electronics books and building electronic by the book. Unfortunately, I feel like I'm not getting the practical knowledge I need to move forward with developing my own circuits.

    As I stated before, I am very hands-on learning. Book reading and instructions following often leave me empty. So, I'm hoping it's ok to ask for some homework from you guys. Something simple and practical, that will require me to do some equations. Of course I'll ask some questions during the process.

    You guys up for it? What kind of small circuit should I attempt to build? Remember I'm VERY beginner here. But I think this will help.
     
  2. crutschow

    Expert

    Mar 14, 2008
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    What type of stuff have you built from the Radio Shack book?
     
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    I was just in a Radio Shack the other day and was delighted to see a decent assortment of kits, from simple flashing LEDs to some real micro controllers. You may try looking thru some of those and find something you like.

    Even the simplest of kits can teach you something practical.
     
  4. SlowCoder

    Thread Starter New Member

    Mar 25, 2012
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    Well, I'm up to about page 50 in the workbook (1) for my project kit. I build the circuit from instructions and it works. Yay! Then I look at the associated schematic, and I try to understand why it works. And that's where I'm doing a whole lot of head scratching. I can even build the circuits looking directly as the schematic. But I still don't understand enough of the "why".

    I have a kit. It has plenty of projects, but I think I need to go a different direction.

    I understand multiple programming languages. I understand the logic and structure behind it. When I was vanilla, I started by reading and typing code from magazines. But that didn't explain HOW it worked for me. The way I ended up learning, for the most-part, was by coming up with a program to write, and building from there.

    This is effectively what I may have to do with electronics. Come up with a project and start building. No pre-drawn schematics or instructions. Just me and my components. Force myself to use the equations involved, and as LOTS of questions. Just like school!
     
  5. SlowCoder

    Thread Starter New Member

    Mar 25, 2012
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    Ok, I'm going to assign myself something ...

    I will try to build a simple 555 timer-based LED dimmer. I will get to understand how a 555 timer works. Will get to use some resistors, and I believe some caps. As it seems to me the 555 is the heart of a circuit like this, I suppose that's where I need to start.

    There are lots of "tutorials" on the web, but I found that they only showed how to connect, but didn't explain HOW the 555 works.
     
    Last edited: Apr 3, 2012
  6. strantor

    AAC Fanatic!

    Oct 3, 2010
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    I would suggest building things you need. Necessity is the mother of invention. I think you learn more by designing things than by building from instructions. You learn what things do, by seeking them out because you need something to do a certain thing. Plus, you have added incentive. It's more rewarding making something functional. What are you going to do with that LED dimmer once it's done?

    EDIT
    why don't you build a PCB milling CNC machine? That would be a good trial by fire. You would be in over your head for 75% of it (that's a good thing - that means you're learning) and the other 25% would be familiar ground for you - coding. You would learn all sorts of stuff about motors, microcontrollers, PC interfacing, sensors, mosfets, all kinds of components, how they work, etc. Once you're done, if you don't want or need the CNC machine you could sell it.
     
    Last edited: Apr 3, 2012
  7. MrChips

    Moderator

    Oct 2, 2009
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    I don't know what your level is but if you have to start from square one I would begin
    with powering LEDs without burning them out. Use Ohm's Law to determine the proper resistance to use.

    Make an LED logic level sensor using one transistor and two resistors.
    Next build an LED flasher using two transistors.

    Move up to LED flashers using 555 timer.
    Add a speaker for audio output.
    Use two 555 timers and make a siren.

    Build a crystal radio.
    Add an audio amplifier to the crystal radio.
    Build a regenerative radio receiver.

    That's as good as any place to start.
     
  8. bretm

    Member

    Feb 6, 2012
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    Instead of using a 555, try making a 555. Get three 5k resistors (the three 5's) to make a voltage divider, a dual-comparator chip to compare the input with the 1/3 Vcc and 2/3 Vcc levels, a flip-flop to remember the state, and a transistor to switch the drain, and make a 555.
     
  9. Wendy

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    Mar 24, 2008
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  10. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    You are not shy in suggesting strantor!

    Knowing the so many things to be solved the idea sounds discouraging to me!
     
  11. strantor

    AAC Fanatic!

    Oct 3, 2010
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    There's another reason I suggested it - lots of people do it. there is even a forum dedicated to doing it somewhere on the internet. He wouldn't be totally without help in unfamiliar territory.
     
  12. SlowCoder

    Thread Starter New Member

    Mar 25, 2012
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    Yes,my philosophy also. I work with retro gaming systems and could use them to "spice up" some of my extra systems. For instance, Atari 2600s have speaker holes in the grills that are prime for installing rotating RGB LEDs.

    Yes, these would all be interesting. Especially the radio. That's one if the projects I've been considering for some time. I eventually want to build a retro-esque wood radio box with large speaker.

    I'd also considered this idea.

    Yes, reviewing now.
     
  13. SlowCoder

    Thread Starter New Member

    Mar 25, 2012
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    Ok, the basics of a 555 timer:
    pin 1: GROUND
    pin 2: TRIGGER. When the voltage is less than 1/3 of the input (pin 8) voltage, it will allow output voltage through pin 3.
    pin 3: OUTPUT. when enabled by trigger, outputs same voltage as is input on pin 8.
    pin 4: RESET. if it drops lower than .7v, cuts off output voltage. Sometimes needs to be connected to V+ directly.
    pin 5: CONTROL. Sometimes used to modify the threshold voltage. Not often needed.
    pin 6: THRESHOLD. When 2/3 input voltage applied, set output to 0v.
    pin 7: DISCHARGE. Not yet understood how it functions.
    pin 8: INPUT VOLTAGE.
     
  14. SlowCoder

    Thread Starter New Member

    Mar 25, 2012
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    Please note that I am doing my best not to look at other schematics, as I am attempting to logic out this circuit on my own.

    This is what I have so far for an LED dimmer. I've attached my schematic, and a picture of the real circuit on a breadboard that should match the schematic.

    Pin 3 (output): I calculated the resistor going from 555's output to LED as: (9v-2v)/.015=466ohm. The 2v is what I believe I'm told is a safe forward voltage, and 15mah is a safe current for the LED.

    Pin 5 (control): At this time I don't know if there's a need to connect it to ground. At this point I'm assuming not.

    Pins 2 (trigger) & 6 (threshold): I think it makes sense that these pins should be connected to receive a variable voltage, probably coming from a charging/discharging capacitor, which should toggle the output on/off.

    This is where my lack of understanding really shines. I don't know where to go from here. Any advice?

    I want to think possibly connecting a capacitor to output, then 2 and 6. My logic is that the cap would charge while 2 is down, then when the when the cap charges and voltage triggers 6, it will cause output to toggle off. Then cap will discharge until it triggers 2 again, toggling output on again. Way off? Yeah, I thought so.
     
  15. Wendy

    Moderator

    Mar 24, 2008
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    You have no voltage source connected to pins 2 and 6.

    555 Schmitt Trigger

    There's that pot again, as a variable voltage source.
     
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