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  • Help picking a PIC?

    Basicly I need to know which would be best. I'm starting out and alot of the tutorials are for the 16F628(A?). Below are the two pics. Is there any big programing difference between the two?

    16F628A
    16F819

    I'm leaning twards the 16F819 because of fetures (5 A/D converters compared to none on the 16F628A). I was planing on using one to get temps from a 1-wire network (I would like to be able to suport alot of temp sensors is the code space going to be enough?).

    EDIT: Oh I was also wondering which I should use for the clock speed. A Crystal or a Ceramic Resonator?

  • #2
    If you're buying your first set of chips, go with the 16F88. It's a good all around chip and has twice the memory of the 819, supports upto 7 10-bit A/D converters. It also includes hardware support for RS232, I2C, and 1-wire buses. Your other option is to go with one of the 18F chips. They offer a simpler programming model (no bank switching) and are supported by the free version of the Microchip C compiler.
    2004 4runner

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    • #3
      Thanks for the info I'm planing on using one of these from sparkfun.com for programing.

      I will check to see if they have the pic you segested.

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      • #4
        Were you talking about the PIC16F688? They have that one at sparkfun.com and it lists that it has 4k of program space and 8 a/d converters.

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        • #5
          Not familar with the 16F819. I imagine it the main difference will be program memory and the io features. AFAIK, not much else differs in the 16F series (outside of the config bits).

          As far as ceramic vs crystal. I use ceramic for the stuff ending up in my car. They aren't as accurate but are less fragile.
          GE Cache Builder | [email protected] |Coolstuff :autospeed.com | bit-tech.net | Nitemax Ultra Pinouts

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          • #6
            I see that most chips have built in 8mhz ones. I may just use that if some one could tell me how to use the internal insted of the external. 4 or 8 mhz is more than enough to poll some 1-wire temp sensors I'm sure.

            Also if any one could help me write the code to read the temp sensors that would be super great. I have seen examples of it on the net but I need to make sure it is for which ever pic I end up buying.

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            • #7
              Originally posted by hcker2000
              Were you talking about the PIC16F688? They have that one at sparkfun.com and it lists that it has 4k of program space and 8 a/d converters.
              16F88
              2004 4runner

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              • #8
                For picking a PIC, it be based on availability, cost, size, hardware design and your programming skills. No need for a built in UART, I2C or PWM as you can do them all in SW. But this is only to reduce the cost of the PIC.

                If you can run the PIC with its internal OSC then do so, this save you 2 I/Os, 2 caps and an XTAL.

                The internal OSC is set on the fuse, the only thing is they are not as accurate as the XTAL. If speed and timming is not an issue then go for it.

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                • #9
                  I also recommend the F88. Literally, it is an improved version of the F819 which is an improved version of the F628A. It does EVERYTHING that those others do, and more.

                  The BIGGEST advantage of the F88 over the F628A is that you can use a bootloader. That means you only have to deal with programming it for real one time (which is a pain, because you either have to pop the chip into the programmer, or deal with ICSP, which always causes headaches) and then you can load everything with a simple, cheap serial adapter from then on. Sparkfun's site has all the info you need on using a bootloader. Trust me, when you're trying to get code to work, it's a million times easier. You can just leave the serial cable connected, and whenever you want to load new code, you just click "download" in the software, and then reset the PIC and in 2 seconds it's all done and ready to run.

                  Also, be aware that you can very easily and quickly get free PICs from the manufacturer. Microchip allows you 2 sample orders per month, and in each order you can have up to 3 each of 5 different PICs (so, up to 30 PICs per month) This is excellent for people who are using PICs for a hobby... believe me, I've been getting samples on and off for years. Not to mention, they usually ship them really fast (they often come from malaysia, and yet arrive in 2-3 days via fedex)
                  But don't take it from me! here's a quote from a real, live newbie:
                  Originally posted by Viscouse
                  I am learning buttloads just by searching on this forum. I've learned 2 big things so far: 1-it's been done before, and 2-if it hasn't, there is a way to do it.
                  eegeek.net

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                  • #10
                    Thanks I think I will go with the 16F88. Will the internal oscilator be able to handle the 1 wire timings?

                    I tryed to get free samples from them but it denied the request for my area of the country so some one (or alot of some ones) must have messed that up for the rest.

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                    • #11
                      how good ... is 16f72 ??

                      mastero

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                      • #12
                        Originally posted by Mastero
                        how good ... is 16f72 ??

                        mastero
                        It depend where you want to use it for?

                        I consider a chip good when its as close as possible to what I want it to do. Including the price, availabilty and ease of use.

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                        • #13
                          Originally posted by hcker2000
                          Thanks I think I will go with the 16F88. Will the internal oscilator be able to handle the 1 wire timings?

                          I tryed to get free samples from them but it denied the request for my area of the country so some one (or alot of some ones) must have messed that up for the rest.
                          You know the clock speed of the sensor needs to run?

                          The internal OSC run at 4Mhz. The PIC MC would be 1MHz in this case, meaning each MC take 1us. Apart from when a jump is involved, in this case 2us.

                          If you can make a tight ASM code you can cram it all in at 4Mhz.

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                          • #14
                            All the info on the ds1822's can be found here.

                            Basicly I would like to poll as many as I can every x amount of seconds and then send the tempatures along with the id of the temp sensor to my computers serial port. I figure I will need a max232 to do that serial portion.

                            EDIT: I know there is a kit that dose that but it only works with 4 temp sensors and if I go that route I won't get to learn any thing. Which is one of the main things for DIY projects. Oh I was planing on programing this pic in C if I can. I'm not sure the steps to convert the C file(s) to the proper hex format yet.

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                            • #15
                              If you want to go with C then your options are a bit more limited unless you are willing to fork out a few bucks for a commercial compiler. Most of the free compilers for the 16F chips are limited in terms of which PICs they support. There is a free (full) beta version of BoostC available that seems to work ok.

                              As for the temp sensor, you'll very likely be OK with the built-in oscillator. If you use the hardware UART, you'll need a level converter to interface with a PC serial port. If you use GPIO line and bit-bang your serial, you can get away without the converter. Most modern PC serial ports use TTL levels. You just have to remember to invert your all the bits when you bang them out.

                              For reading data from the PC, it's best to use a converter IC or build a simple circuit to do the job.
                              2004 4runner

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