1. Post #281
    Gold Member
    demoguy08's Avatar
    February 2005
    3,910 Posts
    Just a quick reminder, the MIT 6.002 free electronics course has now started, if you've not enrolled you best do so right away.
    https://6002x.mitx.mit.edu
    This. Also, I created a thread in General about it: http://facepunch.com/threads/1168312

    Figured it sits better there than here in the programming forum.

    Edited:

    Well, if it dies in General then I'll ask a mod to transfer it here I guess
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  2. Post #282
    LoneWolf_Recon's Avatar
    May 2011
    1,318 Posts
    Crud, school still got me. Guess I'll just stick with their youtube videos
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  3. Post #283
    Gold Member
    VistaPOWA's Avatar
    October 2008
    8,370 Posts
    Damn, electronics is a very danhgerous hobby.

    I just broke my finger accidentally...




    By dropping a 5kg transformer on it.
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  4. Post #284
    Gold Member

    December 2009
    1,322 Posts
    I found a nifty chart to decode resistors from this guys site
    http://worrydream.com/#!/ResistorDecoder
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  5. Post #285
    Gold Member
    VistaPOWA's Avatar
    October 2008
    8,370 Posts
    Just learn the colour coding, way faster than visiting a site every time you need to know the value of one.
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  6. Post #286
    RISC MASTER RACE.
    MIPS's Avatar
    August 2010
    7,077 Posts
    Wasted the evening and a 9V battery dicking around with that tube. It's a total bitch to photograph.





    Hmm. The image is displayed in reverse. Probably because the viewfinder was angled. I'll have to find another one where the tube was inline with the viewfinder which means I'll be looking for an even SMALLER tube.
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  7. Post #287
    Gold Member
    Tw34k's Avatar
    January 2012
    622 Posts
    Could you somehow mirror the input feed or un-mirror the output?
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  8. Post #288
    RISC MASTER RACE.
    MIPS's Avatar
    August 2010
    7,077 Posts
    Everything on the analog board revolves around a BA7125L. That I'm aware of, the only way to flip the video back is through a scan reverser but there must be a way to do it on the PCB.
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  9. Post #289
    Gold Member
    ddrl46's Avatar
    October 2007
    3,629 Posts
    Everything on the analog board revolves around a BA7125L. That I'm aware of, the only way to flip the video back is through a scan reverser but there must be a way to do it on the PCB.
    Or you could just flip around the deflection coils.
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  10. Post #290
    Gold Member

    March 2005
    3,028 Posts
    Or you could view it through a mirror.
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  11. Post #291
    Gold Member
    Chryseus's Avatar
    February 2009
    2,271 Posts
    Well I've had a play around and I thought I'd give you guys my impression of MITx's 6002.

    The course layout is pretty good and covers quite a bit of content, the emphasis on circuit analysis in particular is excellent, however it does assume that you have a decent knowledge of electricity, physics and mathematics, regardless you will need to do quite a bit of independent study.
    Doing the exercises and homework that's assigned each week is pretty easy, it even includes a very nice little circuit simulator.
    To prevent cheating the questions are randomized which is quite nice, although it certainly does not prevent you from using the circuit simulator to get the correct answer.
    The textbook 'Foundations of Analog and Digital Electronic Circuits' is provided for free as well, you can only view it online however as the book is still sold and goes for a whopping 55~ on Amazon, almost worth enrolling just to read the book.

    Overall I'm pretty impressed with it because it has given me more motivation to improve my circuit analysis skills, for absolute beginners however it may be rather difficult to keep up.
    The first homework needs to be in by 16 March so you still have time to enroll.

    Also I got the best question ever:
    How many Joules are there in a BigMac?
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  12. Post #292
    SirCrest is my life, so is yours.
    Goz3rr's Avatar
    October 2009
    7,097 Posts
    Also I got the best question ever:
    What's wrong with that?
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  13. Post #293
    Gold Member
    Chryseus's Avatar
    February 2009
    2,271 Posts
    What's wrong with that?
    Nothing ?
    I just was not expecting it.
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  14. Post #294
    phazmatis's Avatar
    December 2009
    67 Posts
    Hey I have one of those tiny CRTs someplace... I'm glad someone figured out how to wire them up.
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  15. Post #295
    Gold Member
    FoohyAB's Avatar
    July 2009
    928 Posts
    Overall I'm pretty impressed with it because it has given me more motivation to improve my circuit analysis skills, for absolute beginners however it may be rather difficult to keep up.
    I found it really difficult, I was hoping I would be able to get more out of the first few lectures than I did. Then again, I haven't taken any of the prerequisite courses yet, (Well, currently taking physics but we haven't gotten to electricity yet) so I guess I'll just stick with online guides/resources for now
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  16. Post #296
    Gold Member
    SteelReal's Avatar
    May 2009
    1,394 Posts
    I found a nifty chart to decode resistors from this guys site
    http://worrydream.com/#!/ResistorDecoder
    What if you're colorblind? :(
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  17. Post #297
    chipset's Avatar
    November 2010
    2,225 Posts
    What if you're colorblind? :(
    Multimeter.
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  18. Post #298
    Gold Member
    Lapsus's Avatar
    June 2006
    1,069 Posts
    What if you're colorblind? :(
    Somene made an iphone app for that, no idea if there's an android version though. http://nothinglabs.blogspot.com/2011...-photo-id.html
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  19. Post #299
    Gold Member
    Lapsus's Avatar
    June 2006
    1,069 Posts
    [table][tr][td][/td][td][/td][/tr][/table]

    Finally got something done with the buttons, just a simple game controller, the arduino handles debouncing and assembling the packet to be sent to the 8u2, which is running a firmware that makes it identify as a usb keyboard, basically a mashup of the default Arduino usbserial firmware and the LUFA USB keyboard example code.

    Code:
    // Pins
    int buttonpin[9] = {2,3,4,5,6,7,8,9,10};
    int led = 13;
    
    // Variables
    uint8_t buffer[8] = {0,0,0,0,0,0,0,0}; // This is the packet for the lufa+serial mashup running on the 8u2
    unsigned long time = 0;                // Byte zero is modifier keys, 1 is unused, 2-7 are keys being held
    int temp = 0;                          // The state of the button currently being read.
    int button[9] = {0,0,0,0,0,0,0,0,0};   // The state of all the buttons.
    unsigned long lastChange[9] = {0,0,0,0,0,0,0,0,0}; // When the buttons last changed, to debounce
    int numDown = 0;                       // How many buttons are currently down
    int lastDown = 3;                      // How many buttons were down last time through the loop
    int counter = 0;                       // For constructing the packet
    int debounce = 10;                     // How long to ignore button changes in milliseconds
    
    void setup()
    {
      Serial.begin(9600);         // Serial, yay.
      
      pinMode(led, OUTPUT);       // Gotta have blinky lights.
      
      for (int i = 0; i < 9; i++) // Set up pins, blink lights, etc
      {                           // The delay also gives the 8u2 time to do its thing
        digitalWrite(led, HIGH);
        pinMode(buttonpin[i], INPUT);
        digitalWrite(buttonpin[i], HIGH); // internal pull-up resistors are just the best
        delay(20);
        digitalWrite(led, LOW);
        delay(20);
      }
    }
    
    void loop()
    {
      time = millis();
      
      for (int i = 0; i < 9; i++)
      {
        temp = !digitalRead(buttonpin[i]); // Buttons are active low, so invert the reading
        
        if ((button[i] == 0) && (temp == 1) && (lastChange[i] + debounce < time))
        {  // If the button been pressed, and the debounce time has expired
          lastChange[i] = time;
          button[i] = temp;
          numDown += 1;
        } 
        else if ((button[i] == 1) && (temp == 0) && (lastChange[i] + 10 < time))
        {  // If the button been released, and the debounce time has expired
          lastChange[i] = time;
          button[i] = temp;
          numDown -= 1;
        }
      }
      
      if (!(numDown == lastDown))
      {  // Something's changed
        digitalWrite(led, HIGH); // make the light blink
        
        for (int i = 0; i < 8; i++)
        {
          buffer[i] = 0; // empty the buffer
        }
        
        counter = 2; // make sure not to put garbage in the modifier keys
        
        for (int i = 0; i < 9; i++) // and build a packet!
        {
          if (button[i] == 1)
          {
            if (counter < 8) // if we're not out of space. I think we'll be fine with 6 max for now
            {
              buffer[counter] = i + 4; // +4 makes it start a a, so we get a-i as outputs
              counter++;
            }
          }
        }
        Serial.write(buffer, 8); // Send the packet
        digitalWrite(led, LOW);  // turn off the LED
        lastDown = numDown;      // update the change tracking thing
      }
      
    }
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  20. Post #300
    www.bff-hab.de
    Dennab
    February 2009
    7,832 Posts
    looks pretty cool
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  21. Post #301
    SirCrest is my life, so is yours.
    Goz3rr's Avatar
    October 2009
    7,097 Posts
    I'm in need of some help with switches and an arduino actually. It's a DPTP switch, with 6 pins on the bottom (two positions for the switch, i'm guessing two separate channels). So to make this work properly with an arduino, I should apply 5V to the center pin, then wire the top or bottom pin to a digital pin on the arduino and a 10k resistor to the GND right?
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  22. Post #302
    Gold Member
    Lapsus's Avatar
    June 2006
    1,069 Posts
    Assuming you mean DPDT, which is likely because of the 6 pins, the easiest way to wire it up would be to connect the centre of the switch to ground, and the pin to the left or the right of it to whichever pin you want to connect it to.
    From there, when you're setting up your pins in the code, after you set the pin as an input, use digitalwrite to set the pin high, and it'll activate an internal pull-up resistor, meaning when the switch is open, reading that pin will give you a 1, and when it's closed, it'll read 0.

    Looking at the switch from the bottom, each period being a pin, you'd wire it like this.
    Code:
    +-------+
    | . . . |
    | . . . |
    +-|-|---+
      | |
      | +-- Ground
      +---- Arduino pin
    And in your code,
    Code:
    void setup()
    {
      pinMode(yourpin, INPUT);
      digitalWrite(yourpin, HIGH);
    }
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  23. Post #303
    SirCrest is my life, so is yours.
    Goz3rr's Avatar
    October 2009
    7,097 Posts
    Neat, thanks!
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  24. Post #304
    RISC MASTER RACE.
    MIPS's Avatar
    August 2010
    7,077 Posts
    Managed to trace down the +5V and ground pins for certain on that damn resistor network. Started building the replacement network board today.





    Need to double check the rest of the lines before I solder the rest down. This could get nasty.

    Edited: Finished it!


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  25. Post #305
    www.bff-hab.de
    Dennab
    February 2009
    7,832 Posts
    That looks fucking neat, good job man
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  26. Post #306
    LoneWolf_Recon's Avatar
    May 2011
    1,318 Posts
    Pro-MacGuyver'd, I give you kudos MIPS
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  27. Post #307
    chipset's Avatar
    November 2010
    2,225 Posts
    So some years ago my parents replaced the kitchen 19" flatscreen TV because the picture was starting to get sort of wavy, not incredibly noticeable but irritating nonetheless. I took it since wavyness aside it was still working and had a VGA port.
    Some time later I cracked it open looking for faults but knowing terribly little about circuits or TV's I basically just looked for scorchmarks and exploded capacitors.
    I found nothing and it ended up in a closet, recently I had a late night brainwave and realized it might be the power supply. It has an external power brick so that the TV can be easily used in like a caravan where you have 12V unless you're at a trailer park. First thing though I connect the 12v rail of a PC PSU to the TV and hook up my laptop to it, sure enough no wavyness. Following that, I connect the power brick to the oscilloscope and theres noticeable noise plus a disturbingly large spike every once in a while. I crack it open and inspect it and where I expected to find a filtering cap is a 1N4744 15V zener diode.
    Is there a good reason for this or did they just cheap out?
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  28. Post #308
    www.bff-hab.de
    Dennab
    February 2009
    7,832 Posts
    cheap out
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  29. Post #309
    chipset's Avatar
    November 2010
    2,225 Posts
    cheap out
    Good to know. While waiting for a reply I replaced it with a 1000u cap that fit and the noise is significantly reduced but not gone entirely (~50% reduction I think, forgot to write down actual values).
    I just tested it with the modified PSU and the wavyness is gone though I spoke to dad and the reason they replaced it was cause the TV tuner wasn't working, guess I got a new project.
    But hey, fully functional backup monitor, awesome!
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  30. Post #310
    Gold Member
    Chryseus's Avatar
    February 2009
    2,271 Posts
    The winners of my postage only PCB giveaway are:

    Subby
    DrLuke
    marcin1337

    I should be able to take orders by the end of next week.
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  31. Post #311
    www.bff-hab.de
    Dennab
    February 2009
    7,832 Posts
    Yay!
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  32. Post #312
    Gold Member
    Chryseus's Avatar
    February 2009
    2,271 Posts


    First attempt was kind of a major cockup, the photoresist did not spread evenly so next time I'm going to spin it while drying, the exposure was either too short or my developer is shit.
    Etching worked quite well however.

    Hopefully second attempt will give better results.

    Edit

    Turns out I need to mix my developer with NaOH as well, off to ebay I go.
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  33. Post #313
    Gold Member
    0lenny0's Avatar
    March 2010
    387 Posts

    I (hopefully) made a 24V psu. Testing it tomorrow.
    I think i'll better redo the connections when i get some new tin, i really did a messy job on this.
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  34. Post #314
    Gold Member

    March 2005
    3,028 Posts

    I (hopefully) made a 24V psu. Testing it tomorrow.
    I think i'll better redo the connections when i get some new tin, i really did a messy job on this.
    If that's mains coming in on the left, you've got your rectifier/filter on the wrong side. Also, nothing is soldered properly or insulated or mounted. And I'd avoid using a disposable plastic food container as an enclosure on something like this.

    Sorry to be blunt, but mains electricity is serious business. You should really start over from scratch with a proper case, a good iron and new solder/flux. Or work on some low-voltage stuff, then come back to this when your construction skills have improved.
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  35. Post #315
    chipset's Avatar
    November 2010
    2,225 Posts

    I (hopefully) made a 24V psu. Testing it tomorrow.
    I think i'll better redo the connections when i get some new tin, i really did a messy job on this.
    I love the enthusiasm and by all means keep at it, we all had to start somewhere but...
    This is just plain unsafe, if you don't electrocute yourself on that you're bound to start a fire somewhere. Not to mention it won't work cause it's rectified before the transformer as Robo donut said.
    Don't lose heart though, it's a valiant first attempt! At least you got the components right, if in the wrong order...

    Check out some books on the basics of electronics and as a tip, avoid working with mains until you really know what you're doing, that stuff's potentially lethal!
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  36. Post #316
    Gold Member
    Chryseus's Avatar
    February 2009
    2,271 Posts
    What the fuck am I looking at, as Robo said you've completely done it wrong.
    Don't play around with mains until you really know what you're doing, either your going to get shocked or you will cause a fire.

    The only time having a transformer out like that is acceptable is when the primary input is fully insulated.
    Also don't use freeform construction like that, get some pad / strip board and solder it all down, otherwise it's going to look like a total mess (which it does) and greatly increase the risk of shorts.

    Edit

    I rated you zing since you're going to be in for a shocking experience.
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  37. Post #317
    Gold Member
    0lenny0's Avatar
    March 2010
    387 Posts
    I believe that i understand my mistake. I should first go through the transformer and then connect the diode bridge. I understand that it is a mess, all that i usually do is swap components such as replacing a capacitor. I admit that i am kinda ashamed of it but i'm in need of a 24V DC psu so i figured that i could try to build one myself from some stuff i got laying around here. I also plan on using a different enclosure once it's finished. I thought about just vacuum forming one.
    Also i have been working with main power before as i learn how to build infrastructures at school, but we only see a very small amount of stuff about electronics themselves. I might sound like a fool when saying this(i hope not) but i don't expect any of these parts to cause to much harm as i always test stuff outside with a small separate fuse box(don't know if i'm using the right word for it) which should offer protection against short circuiting.

    I'll give it another try later.
    Thanks for the heads up!
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  38. Post #318
    Gold Member
    ddrl46's Avatar
    October 2007
    3,629 Posts
    I believe that i understand my mistake. I should first go through the transformer and then connect the diode bridge. I understand that it is a mess, all that i usually do is swap components such as replacing a capacitor. I admit that i am kinda ashamed of it but i'm in need of a 24V DC psu so i figured that i could try to build one myself from some stuff i got laying around here. I also plan on using a different enclosure once it's finished. I thought about just vacuum forming one.
    Also i have been working with main power before as i learn how to build infrastructures at school, but we only see a very small amount of stuff about electronics themselves. I might sound like a fool when saying this(i hope not) but i don't expect any of these parts to cause to much harm as i always test stuff outside with a small separate fuse box(don't know if i'm using the right word for it) which should offer protection against short circuiting.

    I'll give it another try later.
    Thanks for the heads up!
    Mains -> Fuse -> Transformer -> Diode Bridge -> Capacitor -> Output
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  39. Post #319
    Gold Member
    Chryseus's Avatar
    February 2009
    2,271 Posts
    Mains -> Fuse -> Transformer -> Diode Bridge -> Capacitor -> Output
    nonono

    Mains -> Fuse -> Transformer -> Recitifer -> Filter -> Regulator -> Output
    A 24V Transformer does not output 24V DC.
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  40. Post #320
    Gold Member
    ddrl46's Avatar
    October 2007
    3,629 Posts
    nonono

    Mains -> Fuse -> Transformer -> Recitifer -> Filter -> Regulator -> Output
    A 24V Transformer does not output 24V DC.
    Nononono,
    Mains -> Fuse -> Mains Filter -> Transformer -> Rectifier -> Filter -> Regulator -> Filter -> Output -> Sparks
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