PIC Choosing

Discussion in 'General Electronics Chat' started by R!f@@, Sep 17, 2010.

  1. R!f@@

    Thread Starter AAC Fanatic!

    Apr 2, 2009
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    Hey guys.
    C the image

    [​IMG]


    I like to know which PIC is suitable for this job.
    It's for my PSU, the big one I was making.
    Was about order some PIC's, so thought I'll ask around from more experienced guys.

    key pad and switches are separate. Keypad is used to enter any set value at any given time.
    The LCD will display all the Values.
    Thanks
     
    Last edited: Sep 17, 2010
  2. S_lannan

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    Jun 20, 2007
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    the PIC 16F84A might be a good place to start.
    The PIC 16F88 Has ADC.
     
  3. t06afre

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    May 11, 2009
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    Recommending the 16f84a is like, telling people to use the Ua741 OPAMP. By the way is the PIC meant to a pasive element, or do you want it to take an active part in the voltage/current regulation.
     
  4. tom66

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    May 9, 2009
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    For expansion, why not pick one that has almost everything? Examples that come to mind are the 16F690 and 18F4550/2550.
     
  5. R!f@@

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    Oh !!! I missed that.
    I intend to use a port to control a digital pot for VI adjustment.
    Is this the better way.
    Do you have any other method in mind?
     
  6. t06afre

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    I was asking because Microchip do have series of MCUs designed for power control http://www.microchip.com/stellent/i...AGE&nodeId=2524&param=en027097&redirects=SMPS
    But I guess your design will be more a traditional setup. And The MCU will be used for the Human Machine Interface part
     
  7. hobby16

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    Aug 30, 2010
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    Hi Rifaa,
    It's just me or there is no image ? I know well PICs and may help.
     
  8. R!f@@

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    My bad.....image attached :D
     
  9. R!f@@

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    The Supply is already in use. It's a linear supply
    Here's the post
    http://forum.allaboutcircuits.com/showthread.php?t=35039

    The Microchip shows SMPS.
    I don't need that. Even a DAC port is enuf to control the V and I...no?
     
  10. Markd77

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    Sep 7, 2009
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  11. hobby16

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    @Rifaa
    If you need 2 DACs for I & V setpoints (I say "if" since I don't know the final details of your PSU), you'll need two PWM. I agree with Mark a 28 pin uP is required. So you can start with the very ubiquitous 16F876A, I've designed this circuit years ago with a rotary encoder : http://faztech.free.fr/uploads/accu.PDF
    There are many upgrades of this old uP but it's a good start : large Flashrom to program in C, good availability...

    P.S. I don't see the need of a keypad since a rotary encoder with 2 or 3 pushbuttons & LCD is a more than complete user interface. Ensure the rotary encoder is connected to an interrupt driven port (RB4...RB7) since polling it by firmware without missing steps would be really ressource consuming !
     
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  12. R!f@@

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    I was hoping to get 16F877. Will this suffice

    Mark, How does this compare to ur suggested PIC's
     
  13. Markd77

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    It should be plenty. That one doesn't have an internal oscillator, so would need a crystal/resonator. The 887 is an updated version with an internal oscilator
     
  14. R!f@@

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    then 887 it is
     
  15. SgtWookie

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    PIC16F877 is an obsolete uC. PIC16F887 is a current IC. However, it's a 40-pin IC.

    Look at the PIC16F193x class of uC's - they're a quantum leap ahead of the PIC16F88x uC's. They're very new, and there is not a lot of support for them yet, but B. Kneutsen's CC5 does support it; it's available in freeware, it interfaces with the Microchip dev env, and it's available as freeware. Did I mention free? Free is a good thing.
     
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  16. R!f@@

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    40 pin is too much.

    Is B. Kneutsen's CC5 a new compiler
     
  17. Markd77

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    For 28 pin go for 886. Or one of the new ones maybe 16F1933.
    The new ones are a definate improvement, but there will be less code examples for them and less people who have used them.
    I will probably get one of the smaller ones when I need enough stuff for another order.
     
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  18. t06afre

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    As I have understand you will be using LM723 as the regulator. For the voltage setpoint you may use ad digital pot or a DAC. Do you have a link to your schematic. The thread you pointed to is quite big. And I need to see your current limiting setup, in order to decide what is best. But I think I will place my bet on a digital pot. I do not think you will need 40 pins. The best thing is to use a chip you know you can replace easy.
    I also think the HI-tech C compiler is the best. The Hi-tech C compiler is free to download from here http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1406&dDocName=en542849
     
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  19. R!f@@

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    I have Hi-tech C installed already but I am not familiar with it yet.
    I see most people are using Hi-tech.
    I guess I have to study it.

    As for the schematic, I will upload it and let u guys know via a PM.
    I haven't yet set up the current limit stage. My design is based on 723. So will the current limit stage.
    I guess I have tested the voltage power regs enuf without a current limit.
    I've had dead shorted the out puts, but only once the driver blew only.
    Other times the primary fuse blows. I did not have a secondary fuse before, but now it's already in circuit.

    Now I realize the advantage of having genuine power transistors. They are pretty rugged. The wiring is pretty heavy gauge too. When a short occurs nothing smokes like in other PSU's. Only fuse blows :D.

    Current limit stage is based on 723. I'll show u after completing it.

    I am searching for a μC ahead because, on sunday retched will be getting me a pickit3 and the TI kit, so with it I planned to buy some PIC's.

    I have a question though. Instead of using a digital pot, what if I use a DAC port to control the Vadj of the Voltage reg. This way I can have a higher resolution.
    With a pot, the voltage resolution is based on the pot resolution, which is it's step, right?

    I wish to change the Vout in 10mV resolution. Cause I wish to have a autoranging 4 digit voltmeter. from 00.00VDC to around 40.00VDC.
    At lighter loads My design can go upto 40VDC without losing regulation.
    But for heavy loads I plane to stay at 30VDC

    What do u say abt the control technique I am choosing. Should I use a DAC directly connected to the 723 or via a digital pot.
    Based on this method I like to choose the PIC.

    I think 28 pin will do, but which PIC has the necessary DAC ports.
    I think I need a PIC with two ADC's and two DAC ports.
    Is such a PIC available?
     
  20. SgtWookie

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    Well, the PIC16F193x series have both a multiplexed 10-bit ADC and a multiplexed DAC; but the DAC has only 32 steps.

    Keep in mind that with digital pots, your output will be limited to the Vcc that is supported by the digipot. For example, if it's rated for operation at 5v, that's the highest output voltage you'll get.

    Digital pots are usually also quite limited as to their current source/sink ability.

    Instead of PMing people with the address, just post a link directly to your post that contains the current schematic. That way everyone can follow the discussion.
     
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