making a 555?

Discussion in 'The Projects Forum' started by ale2121, Apr 15, 2009.

  1. ale2121

    Thread Starter Active Member

    Mar 20, 2009
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    hi,
    for learning purposes only, i'm curious about making a 555 chip, just to see the internal guts and watch how it works. Has anyone done this, and can you point me to a schematic that will get me started?
    thanks.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    Have you got a data sheet for a 555? The necessary functions are indicated.

    That is sort of interesting, but a 555 is so cheap and available that it would be like reinventing the wheel. As a learning tool, though, duping the IC might be valuable.
     
  3. ale2121

    Thread Starter Active Member

    Mar 20, 2009
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  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    Now you see why it's easier to just buy one. Those transistors are part of the IC, and so don't translate to discrete part numbers. You could grab some 2N2904's for NPN and 2N3906's for the PNP's, and see what happens.

    Another approach would be to work from the functional block diagram. Use components to fill the block functions, like a CD4013 flip flop, and some voltage comparators like an LM311.

    If you wish to follow the transistor design, you would do well to read up on differential amplifiers and current sources.
     
  5. bertus

    Administrator

    Apr 5, 2008
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  6. italo

    New Member

    Nov 20, 2005
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    believe or not all chip are done on a giant screen as a mask and reduced to mm as a silicon chip. the ratio of 639 is done with a laser. you can biult it with dicrete components yes but what you will learn is how descrete conponents work first.
     
  7. mik3

    Senior Member

    Feb 4, 2008
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  8. jorgeron

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    May 28, 2009
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    You can make your own "pseudo" ic . just build the circuit from discrete components (test it and then test it again 10 more times) and then pot it in epoxy or acrylic resin, etc. i have done it. its a waste of money, a waste of time, but lots of fun.
     
  9. Mike Mandaville

    Active Member

    May 27, 2009
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    I used to have sex, but then I discovered that it's easier to pay someone else to perform that function for me. No, seriously, my favorite digital logic book is Don Lancaster's "The CMOS Cookbook", which is laid out much the same as any other college textbook on digital logic. In other words, first the "innards" of the chips are explained in detail, then the chips themselves are explained. I would fall on the side of encouraging anyone who wants to actually understand those innards to put them into hardware.

    Historical recreation is one of my favorite pastimes. I ordinarily do not bother to tell people that what I am actually doing is engaging in fundamental research. Other people do not usually understand. I understand myself, though, and that is what matters.
     
  10. mik3

    Senior Member

    Feb 4, 2008
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    Maybe you can understand the internal structure of an IC described in the book (even simplified) but you cannot make an IC at home.
     
  11. Wendy

    Moderator

    Mar 24, 2008
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    You can do what the chip designers used to do, and build the same circuit with a bunch of descrete components. This was what the OP was wanting to do. Personally I prefer letting the magic smoke out learning the chip (or better yet, not).
     
  12. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    If you want to do something relevant for the 21st century, program a 12F683 to duplicate an LM555. Vss and Vcc will be different of course.

    John
     
  13. radiohead

    Active Member

    May 28, 2009
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    Bertus, that was a great link to the 555 tutorial.
     
  14. mik3

    Senior Member

    Feb 4, 2008
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    What do you mean exactly?
     
  15. jpanhalt

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    Jan 18, 2008
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    I mean a 555 emulator using an 8-pin PIC. I am not sure it can be done, but the analog inputs of the 12F683 may allow it to be done. The power pins are different between the two. It was just something I thought of trying to help me learn the analog functions.

    Whether it works or not, I view the attempt as more challenging and educational than simply duplicating a published circuit for the 555 using discrete components.

    John
     
  16. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    It would be pretty easy to to a simple 555 emulation with a PIC, you only need 2 analog inputs for the two threshold voltages pin 2 and 6. However top speed of the "E555" would be linited as the PIC can only read one ADC input at a time so there is a need to switch between the 2.

    If it's just emulating a typical 555 oscillator it's easier as you only need to monitor pin 2 on the way down and pin 6 on the way up.

    Maybe a faster "E555" could be made using a PIC with inbuilt comparators and somehow setting the comparators to 1/3Vcc and 2/3Vcc either internal or external referenced.
     
  17. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    That was my point, but I couldn't find any examples on searching the Internet. Thus, it might be easy, relatively unique, and a good learning exercise. One would have to learn how the 555 worked, not just solder some pieces to gether.

    I hope someone will spoil my fun and post the assembly code here. Bill Marsden may even include it in his 555 section.

    John
     
  18. bundick

    Active Member

    Dec 19, 2007
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    mik3 answerd my question; what'd they do for timers before the "busy chips" came along? Thanks mik.
     
  19. SgtWookie

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    Jul 17, 2007
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  20. mik3

    Senior Member

    Feb 4, 2008
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    What was the question?
     
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