1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

15 Channel RGB (45 LED) Color Wave Using PIC16F628A

Discussion in 'Microcontrollers' started by Chipwizard, Jun 15, 2011.

  1. Chipwizard

    Chipwizard New Member

    Joined:
    Dec 14, 2009
    Messages:
    146
    Likes:
    0
    Location:
    Florida, US
    Want to read this new data in details before posting...
     
    Last edited: Jul 16, 2011
  2. Chipwizard

    Chipwizard New Member

    Joined:
    Dec 14, 2009
    Messages:
    146
    Likes:
    0
    Location:
    Florida, US
    Sorry about my previous post as I came across additional and interesting information reading up...
    Before I share what I have found, let me start by saying that one transistor does not make for a TTL device. I stand corrected there. The project deals with individual transistors and not TTL.
    TTL devices are broken down into two major families: Standard TTL, Schottky TTL (Clamp/transistor)
    Standard TTL: Have a high input resistance, fairly low time delay (fairly good speed), low input current (about 1ma), good sinking (21.5ma) and not so good in sourcing (2.6ma)
    Schottky TTL: High input resistance, slightly higher input current (1.4ma), lower time delay (higher speed), do not operate in saturation (operate in active region), excellent for both sourcing and sinking since they have a much higher current gain and a low output resistance, excellent turn on and turn off time for fast speed switching (higher frequency).

    I also found good answers to my earlier questions in regards to availability of higher currents in PIC's:
    By increasing the thickness of supply bus lines in PIC, you increase the internal capacitance of the device compromising switching time. Also there is a limitation of how close internal transistor can get to each other due to power dissipation. Increaing number of transistors or size of the transistors to acoomodate higher currents would require a higher foot-print on the chip (area). With everything else jammed packed into these chips (CPU, CLK, ROM, RAM, Driving Transistors, clamp diodes, and so on), chip real estate is limited.

    Source: Book of "Microelctronics Circuits" by Adel Sedra & Kenneth Smith. Book was used in school of EE in Georgia Tech.
    TTL Logic: Pages 915-934
    Schottky TTL Families: Pages 935-941
     
  3. Chipwizard

    Chipwizard New Member

    Joined:
    Dec 14, 2009
    Messages:
    146
    Likes:
    0
    Location:
    Florida, US
    As much I do not like to hear it, it is true that microcontrollers in general are not designed to be direct-drive devices. They need to sit in command position slaving other devices to drive other circuits and devices.
     
  4. dave

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    -
    Likes:
    0


     
  5. Sceadwian

    Sceadwian Banned

    Joined:
    Oct 27, 2006
    Messages:
    14,047
    Likes:
    141
    Location:
    Rochester, US

    Thank you for confirming what I was saying, the information you provided was great as far as clearing up my confusion about the output current requirements. The language logic in my head had me seeing 16ma for an output of 0 to mean that 16ma had to be flowing to read the 0 output, not that sensible electrical equivalent that it can sink that much current. My experience is with micro controller devices not TTL devices so it makes perfect sense now that that the current requirements are to offset the TTL circuits bias currents. Modern micro controller I/O 'pins' are actually compound CMOS devices in and of themselves, so the translation of technologies threw me for a loop.

    I'm not sure why you don't like to hear that it's true that micro controllers in generally are not designed to be direct drive devices... Micro controllers are all at their heart (in my honest opinion) supposed to be general purpose devices. Microchip makes many different versions of PICs leaning towards one or more specific usages with their peripherals and drive ability, and various other makers market their products on more general or more specific usage considerations.

    It's a hard world for chip makers nowdays.
     
  6. Chipwizard

    Chipwizard New Member

    Joined:
    Dec 14, 2009
    Messages:
    146
    Likes:
    0
    Location:
    Florida, US
    I guess I wished they had more powerful I/O's. That's all. I am glad for your response since it got me looking things up to get to some of my answers. Now I know the specs and limitations of PIC, I can put them to better use.

    By the way before we drift away from the topic. In the same book, I did look up more details on transistors (not TTL) confirming the 8ma base current for switching and partial saturation. They said the same thing as to use 4ma minimum but double it for best results (8ma). This is pretty useful info for common transistor we use (2n3904). It's hfe (current gain) is about 30. (Ib=8ma, Ic=240ma given and take)
    Regards,
    Rom

    P.S.: I posted the begining of RGB18 project and explained more of source code, layout, color mapping of RGB15 in details. If any one is interested to know, look it up. Cheers.
     
  7. Sceadwian

    Sceadwian Banned

    Joined:
    Oct 27, 2006
    Messages:
    14,047
    Likes:
    141
    Location:
    Rochester, US
    I understand your dislike of the I/O limitation, however there are physical considerations involved, the difference between power devices and logic devices are profound from a manufacturing perspective.
     
  8. Chipwizard

    Chipwizard New Member

    Joined:
    Dec 14, 2009
    Messages:
    146
    Likes:
    0
    Location:
    Florida, US
    Here is a programming model for RGB15.
     

    Attached Files:

    Last edited: Jul 18, 2011
  9. militel

    militel New Member

    Joined:
    Jun 26, 2012
    Messages:
    1
    Likes:
    0
    I want make 15 channel led but and I have a request: do you have a functional HEX for the 628?
    I'm not too good at programming
    thanks
    I am from Romania
    [MODNOTE]Link deleted..[/MODNOTE]
     
    Last edited by a moderator: Aug 26, 2012
  10. 4pyros

    4pyros Well-Known Member Most Helpful Member

    Joined:
    Oct 22, 2010
    Messages:
    4,368
    Likes:
    282
    Location:
    Pennsylvania, USA
    This is an old thread start your own.
     

Share This Page