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Thread: Arduino Nano thought experiment

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    I2C IC's is definitely an option @DrifterNL for expanding the I/O ports. Some may argue that they are harder to program, but this could be a good time to learn.

    At one point I did explored the use of PCA9685PW chip for adding another 16 PWM pins. If I only needed one, then okay but in the situation I was looking at the costs of these 'extras' was rising quickly.

    Mark

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    Quote Originally Posted by DrifterNL View Post
    I wonder if using the IC bus with 8 * PCF8574 and 8 * PCF8574A would be a solution?
    Hadn't considered I2C, but with those 2 chips, it certainly could be a solution.

    Here are the advantages / disadvantages that I can see:

    Advantage: Lower chip count with I2C. I would eliminate 1 decoder and 2 bus driver chips.

    Disadvantage: Higher chip cost. A PCF8574/A costs more than any of the TTL chips currently in the circuit. I don't think the cost savings on the 3 eliminated chips covers the higher cost of the PCF.

    Advantage: The interrupt feature on the PCF8574 means that the program timing is not as critical. Wouldn't have to constantly poll the inputs.

    Disadvantage: I2C is serial. Probably not an issue given the interrupt capability. Trade-off with having to poll the inputs ?

    Advantage: The I2C communication protocol is already built into a library, so my program would be a bit simpler. I wouldn't have to be concerned as much about the timing issues.

    I think I'll put some of these on order ....


    GDR

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    Quote Originally Posted by Gary Rowan View Post
    I think I'll put some of these on order ....
    Well, the PCF8574 chips arrived a couple of days ago. Unfortunately, it's super-busy time @ work so I haven't had the time to do much more than study the data sheets (anyone speak Greek?).

    I do have one question about the interrupt feature on these chips. If I am using several of the chips as inputs, can I tie all of the PCF interrupts together to one of the Arduino interrupt pins, or do I need to run them through a logic gate to keep them isolated from each other?

    Also found references to the MCP23017 16-Bit I/O Expander with Serial Interface. Anyone have any experience with this chip? Looks like a PCF8574 x 2.

    GDR

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    Quote Originally Posted by Gary Rowan View Post
    I do have one question about the interrupt feature on these chips. If I am using several of the chips as inputs, can I tie all of the PCF interrupts together to one of the Arduino interrupt pins, or do I need to run them through a logic gate to keep them isolated from each other?
    Yes, you can tie all the interrupts together.
    The Interrupts are open drain outputs, all you need is a pull-up resistor on the arduino end.

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    Default Chip, socket cost greater than Microprocessor

    Hi GDR,

    By the time you add the cost of the latch chips, sockets, output connectors and amount of wires required. Microprocessors can be purchased for less than $5, it might be cheaper to use multiple microprocessors tied together using serial communication. Each one can monitor several detectors, drive several signals, has a unique address and can be called from a master microprocessor that handles your "interlocking" logic. You only need three wires for the ground, serial data in and serial data out. All the distributed wiring would be local and much shorter.

    The advantage of a single microprocessor system is only one program is required...but it's a much more complex program to develop and test.

    The advantage of distributed microprocessors is reusing the same small program in all the slave microprocessors and separating the "interlocking" logic as a separate program.
    Happy Modeling

    Bruce

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