whats the difference?

Discussion in 'Embedded Systems and Microcontrollers' started by vane, Dec 19, 2008.

  1. vane

    Thread Starter Active Member

    Feb 28, 2007
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    i am making a PIC16F84 serial servo controller, but all crappy maplin had was PIC16F84A, they said it was the same thing so i got one but it doesn't seem to be working, the site i saw it on says it is for a ordinary 84 which brings me to the question, what is the difference?
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    The data sheet from Microchip Technology should make it clear.

    What's not working?
     
  3. Papabravo

    Expert

    Feb 24, 2006
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    All questions of this type can be resolved by consulting the datasheet. Can you be a bit more specific about what does not work? Like do you have an aaplication that works with a 16F84 and not with a 16F84A.

    AFAIK the A version has improved electrical specifications, but is otherwise compatible. Consult the datasheet, that's what it is there for.
     
  4. vane

    Thread Starter Active Member

    Feb 28, 2007
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    the data sheet just looks like a load of graphs and random numbers to me.
    with the serial servo controller, the servo motor just moves randomly around, when you send the information via the serial port to it nothing happens, i have re done it on bread board so i dont ruin the parts soldering and resoldering them onto the strip board, there is no real correlation between what i input and what moves the servos, it is just random positions it moves the servo to, i am really lost :s
     
  5. hgmjr

    Moderator

    Jan 28, 2005
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    Are you building your servo from an existing design?

    hgmjr
     
  6. vane

    Thread Starter Active Member

    Feb 28, 2007
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  7. hgmjr

    Moderator

    Jan 28, 2005
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    Just wondering. Did you download the program into the PIC?

    hgmjr
     
  8. vane

    Thread Starter Active Member

    Feb 28, 2007
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    yeah i did, the servo motor does move, it is just random though, do you want me to upload a pic of the setup?
     
  9. hgmjr

    Moderator

    Jan 28, 2005
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    Sure. It might give us some ideas.

    hgmjr
     
  10. vane

    Thread Starter Active Member

    Feb 28, 2007
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    it iws not allowing me to upload pics, do i need to supply voltage to the DB9 connector? cause i have heard something about supplying power through pin 9 :s
     
  11. hgmjr

    Moderator

    Jan 28, 2005
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    Have you gone through and double checked the wiring? Also check the quality of your connections.

    hgmjr
     
  12. vane

    Thread Starter Active Member

    Feb 28, 2007
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    it is done on bread board so i havent soldered it and i am almost certain it is wired correctly
     
  13. hgmjr

    Moderator

    Jan 28, 2005
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    I suspect that the reason that you were unable to post your jpeg file of the prototype is that the size of the picture exceeded the max file size of 293 Kbytes. Can you reduce the resolution of the picture and try attaching it again?

    hgmjr
     
  14. vane

    Thread Starter Active Member

    Feb 28, 2007
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    i dont have any way of doing that
    the ceramic resonator says 400, does that mean its a 4mhz one?
    also what does bau rate do?
     
  15. hgmjr

    Moderator

    Jan 28, 2005
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    It is a 4 MegaHertz crystal.

    The bitrate is set by the program to be 2400 bps.

    hgmjr
     
  16. hgmjr

    Moderator

    Jan 28, 2005
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    I'm surprised that the design does not include an RS-232 interface device. I think that there may need to be an inversion in the line that may be lacking in the circuit you have.

    hgmjr
     
  17. vane

    Thread Starter Active Member

    Feb 28, 2007
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    ah i think it works now, i think i just needed to set the baud rate in the program they made, although every few times i set it to a different position it wiggles around a random position then after a second of wiggling it goes to that position
     
  18. hgmjr

    Moderator

    Jan 28, 2005
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    The 22K resistor is a good precautionary protective measure to keep the negative going RS-232 input to the PIC from damaging the PIC.

    If you have a diode like a 1N4148 or 1N914, I would connect it to pin 17 of the PIC. The diode will better protect the PIC input and clamp it so that it will not go negative relative to ground. The cathode should connect to pin 17 and the anode would be connected to ground.

    hgmjr
     
  19. vane

    Thread Starter Active Member

    Feb 28, 2007
    181
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    we don't really keep diodes, we don't use them very much. the only diodes i have are LEDs, thanks for all your help so far!

    i have tried to make my own application to control it but it does not work, what they are telling me to send via the serial port
     
  20. Papabravo

    Expert

    Feb 24, 2006
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    Actually you need to read the text. Looking at the graphs comes later.
    Here is the side by side comparison from the microchip website which you could easily have found for yourself
    http://www.microchip.com/stellent/i...eId=2533&product1=PIC16F84&product2=PIC16F84A
    The change in flash memory technology let them put more words on the die so you went from 1K words to a really crappy(your words -- not mine) 1.75K words. some people just don't know when they are well off.
     
    Last edited: Dec 20, 2008
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