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Half way done and wish I had made a PCboard

Discussion in 'General Electronics Chat' started by MrDEB, Jul 20, 2014.

  1. MrDEB

    MrDEB Active Member

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    Building a 8 x 32 led matrix using 4 - TPIC6B595 chips (similar to 74hc595 but handles higher currents) 1 - uln2803, 4 - 8x8led matrix and one 40 pin pic.
    All done with point to point wiring but wish I had done a PCboard. MIGHT have been easier.
    One jumble of wires. Just wish I had a wider choice of wire colors so I could do a better job of color coding but it is what it is.
    Been using a continuity tester after each section is done. LOTS of daisy chains as well.
    Tomorrow we insert chips and hopefully write code to test. Using Swordfish.
     
  2. JonSea

    JonSea Well-Known Member

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    I don't have a clue how you have your circuit arranged, but...

    The TPIC6B595 can only sink current.

    The ULN2803 can only sink current.

    If the TPIC6B595s sink current for each column and exactly one column is ever illuminated at the same time (as should be the case when multiplexing an LED matrix), one port of the PIC can drive the rows (each port pin through its own current-limiting resistor) at up to ~20mA as long as the overall limits of the PIC aren't exceeded.

    I'm not sure where the '2803 is in your circuit, but I'm almost certain it's not going to do what you want it to.


    You might be better off using one of the 32x8 LED arrays from Sure Electronics on eBay for around $15. They use an HT1632C LED driver chip to handle all the busy work of multiplexing. You just send the data to be displayed over and SPI- like interface and the chip handles the rest.


    image.jpg
     
  3. MrDEB

    MrDEB Active Member

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    Dang it I took the long way around for sure. Wish I had knowen about the HT1632C setup.
     
  4. dave

    Dave New Member

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  5. MrDEB

    MrDEB Active Member

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    Here is what I did for connections. Hopefully it will work.
    http://ts3.mm.bing.net/th?id=HN.608022886628919322&pid=1.7
    researching I found several references to using the 74595 or the TPIC6B595 in this manner.
     
  6. throbscottle

    throbscottle Well-Known Member

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    I built a jumble of wires recently with pic and logic to test display and switching - was ok until it developed a fault!
     
  7. JonSea

    JonSea Well-Known Member

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    No. The TPIC6B595 has a similar function to the 74HC595 in that it's a shift register. Its outputs are designed differently for high current/ high voltage operation (from TI):

    This is going to be the case for any logic chip that can handle >5 volts.
     
  8. JonSea

    JonSea Well-Known Member

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    Just to head off any "but you suggested the TPIC6B595..." comments, recall:

    I suggested the TPIC6B595 as an alternative to '595 shift registers controlling ULN2003s...meaning they would sink current.

    Sorry for your confusion, but it's not going to work as you layer it out.
     
  9. MrDEB

    MrDEB Active Member

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    EGADS this is getting confusing at best. Going by the data sheet it appears that I have it right but perhaps my voltage is wrong?? but the link I posted shows it should work??
     

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  10. JonSea

    JonSea Well-Known Member

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    No. The TCIP6B595 can only sink current. No matter how you want or expect it to work, this chip can only act as a ground in the same manner as a ULN2003.

    That would be the meaning of the word drain in the data sheet.

    image.jpg

    You can also see in the data sheet that the chip can only provide a ground connection on the output.

    image.jpg
     
    Last edited: Jul 21, 2014
  11. MrDEB

    MrDEB Active Member

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    Not to be argumentative but the data sheet shows the load between the DRAIN outputs and GROUND
    http://www.electro-tech-online.com/attachments/rev-595-jpg.87426/
    I have it all connected up and in process of trying to write some code to get it working if indeed it will but??
    Having used SHIFT.bas only once I need to perhaps assemble a one chip circuit on a breadboard with 8 leds. I viewed a website that showed using similar. Will try and locate and re read.
     
  12. tronitech

    tronitech Member

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    The loads are between the positive of a battery, presumably representing the power load supply and the drains!
     
    Last edited: Jul 21, 2014
  13. JonSea

    JonSea Well-Known Member

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    The data sheet is clear about this. It's an open drain chip. It can ONLY SINK CURRENT.

    Of course, you're welcome to imagine anything you like.
     
  14. JonSea

    JonSea Well-Known Member

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  15. JonSea

    JonSea Well-Known Member

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  16. ronv

    ronv Well-Known Member Most Helpful Member

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    Your circuit needs to put 5 volts on the anode of the LED while the 2803 puts ground on the cathode. Your chip can not put 5 volts on the anode the way it is hooked up. You may be able to salvage your work by using the chip to turn the LED off instead of on.
     
  17. MrDEB

    MrDEB Active Member

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    I see my error. Now to see if I can salvage as per ronv's suggestion or purchase said unit Jon suggested BUT I need this up and working by August 17th if I can or else forget the project. As I stated we spent $4100 on new refrigeration equipment and I wanted to "brag" about how cold our beer is during the county fair.
    Getting a componet from China takes a long time sometimes 3 weeks.
     
  18. Pommie

    Pommie Well-Known Member Most Helpful Member

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    You could order some max7219 chips. Each one will drive one 8x8 display.

    Mike.
     
  19. JonSea

    JonSea Well-Known Member

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    You can probably still make this work. Arrange the anodes in rows and the cathodes in columns.

    Drive each row via a current limiting resistor from one pin of a port (one port used for the rows). Use the shift registers to SINK current from each column, one at a time. Only one column is illuminated at a time, so each port pin only drives one LED at any instant. Much like the illustration below, with the ULN2803 replaced by the high power shift resister.

    image.jpg
     
  20. JonSea

    JonSea Well-Known Member

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    Well, you could make a label "The beer temperature is:" and use two seven-segment digits.
     
  21. JonSea

    JonSea Well-Known Member

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    It's unfortunate that you don't carry over any knowledge from one project to the next; it's as if you flush anything that might have been learned down the drain.

    Because in fact, I already discussed exactly what you're trying to do now way back when you were trying to scroll a message across a single 8x8 matrix.

    If you had continued along the same path, expanding on the method I'd explained back then, you'd have a working circuit and a head start on the software development.

    In general, the options for adding matrices (or seven-segment digits for that matter) are:

    1. Multiplex more matrices. The down side is that for each matrix you add, the smaller percentage of time each column is illuminated, and the dimmer the display gets. You can increase the LED current to compensate for this (with most arrays) since each LED is on for only a short period and off for most of the time, but if the software stalls and stops scanning columns, continuous high current through one column will destroy LEDs.

    2. Use a dedicated driver chip per array as Mike suggested. This has the advantage that the display can be driven at full brightness no matter how many arrays are used. Dedicated driver chips like the MAX7219 take care of all the busy work. The downside is that update speed may fall off if many arrays are used.

    3. Use a single chip solution like the HT1632C. This takes care of many details and makes it easy to address any dot.
     

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