Circuit Overlay Modules

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  • idbruceidbruce Posts: 6,134
    edited 2020-09-06 - 15:02:48
    Peter
    if only you could put down that mind-numbing beer :)

    For the last 10 years, my drinking tendancies have varied due to various circumstances, such as trying to build a business, my mother's illness, my mother's death, and getting back on track. At the current moment, I imbibe maybe once a month. I was overdue for a beer :)
    Now when I say an RC circuit, then that's all it is, a series resistor from a Prop I/O connected to a cap to ground. This forms a simple filter that averages the duty cycle of the high-frequency waveform so at a 25% duty cycle produces 1/4 of the 3.3V or 825mV approx. So effectively it's like a DAC. I'd use something like 1K and 0.1uF.

    There are two counters per cog and setting up a counter for duty cycle mode is dead simple and even if you just set it once in software you can do away with a trim pot. But if you can vary the current dynamically you can overdrive the stepper during acceleration and reduce the current when you are stepping slowly etc. This also helps the chip thermally too. Having options, especially when they are so simple never hurts.

    As I said, I liked your suggestion, but I did not want to be tied to it. So how is this for a compromise?

    EDIT: I suppose in reality, I could just eliminate JP11, because JP10 ultimately determines whether Propeller I/O Pin 0 is used or not.

    schematic.jpg

    board.jpg
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  • Hey, it's up to you. I know what I have done and will do and I'm only empowering you with what I consider a better choice, not a compromise :)

    BTW, I've used Prop RC DACs for audio and LCD contrast and also through opamps for 0..10V stuff etc. They work really well. To not use them would be like adding a 555 timer to the Prop rather than using a counter to generate a frequency etc.
  • idbruceidbruce Posts: 6,134
    edited 2020-09-06 - 15:13:29
    Hey, it's up to you. I know what I have done and will do and I'm only empowering you with what I consider a better choice, not a compromise :)

    BTW, I've used Prop RC DACs for audio and LCD contrast and also through opamps for 0..10V stuff etc. They work really well. To not use them would be like adding a 555 timer to the Prop rather than using a counter to generate a frequency etc.

    I hear ya loud and clear :)

    However, considering what I am proposing in this thread, there are only 16 Propeller I/O pins available, but of course an I/O expander module could be added. I can easily imagine 10 modules stacked on top of each other, and without an I/O expander, the Propeller I/O pins would be getting scarce :)

    It is always nice to have options :)
  • idbruceidbruce Posts: 6,134
    edited 2020-09-06 - 15:28:34
    However, considering what I am proposing in this thread, there are only 16 Propeller I/O pins available, but of course an I/O expander module could be added. I can easily imagine 10 modules stacked on top of each other, and without an I/O expander, the Propeller I/O pins would be getting scarce :)

    However, modules that are created with I2C compatible IC chips could help to alleviate I/O pin availabity problems.
  • However, modules that are created with I2C compatible IC chips could help to alleviate I/O pin availabity problems.

    That is actually a VERY good idea :) If I do say so myself :)
  • I dug back into my projects and found a board from 8 years ago that I did for my L6470 microstepper modules. It looks like one of my test prototypes. I had done up a pcb that fitted the case, fitted the connectors that needed to be fitted and it did everything I wanted. So rather than stacking upwards which sounds great but in practice you need to package it, access it, and connect to it, I choose to go sideways with a simple I/O bus. I had a whole series of different Puppy modules that I could swap around.
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  • I dug back into my projects and found a board from 8 years ago that I did for my L6470 microstepper modules. It looks like one of my test prototypes. I had done up a pcb that fitted the case, fitted the connectors that needed to be fitted and it did everything I wanted. So rather than stacking upwards which sounds great but in practice you need to package it, access it, and connect to it, I choose to go sideways with a simple I/O bus. I had a whole series of different Puppy modules that I could swap around.

    Very nice :)
  • If you redesigned your L6470 puppy into an overlay for this thread, it would be nice :)
  • This thread and concept will eventually catch on :wink:
  • idbruceidbruce Posts: 6,134
    edited 2020-09-06 - 16:01:13
    I have visions of granduer :)

    EDIT: That is the beer talking :)
  • idbruce wrote: »
    If you redesigned your L6470 puppy into an overlay for this thread, it would be nice :)

    That overlay board was designed at the request of an educator wasn't it. Probably for the purpose of a quick hack in the classroom. I would hope that what you are doing is not a quick hack and that you are not back in school either.

    You can however just add sockets for these modules although I wouldn't want to stop you from making up your own board. I'm kinda busy myself with the P2D2 family of modules at present but even so I just would never want to work with those overlay modules. Why don't you just design your own custom board with the Prop and all the other stuff you need on it? Do you have a block diagram or something, or even a spec on what you are trying to achieve?

    btw, the P2LAB board has pin headers for plugging in matrix boards or custom modules, as well as provision for two mikroBUS modules as well as my Puppy modules. The whole board is designed to drop into a standard 170x120mm ABS enclosure too if need be, complete with industrial screw terminal sockets etc. It is designed to be run by a P2D2 but I am meaning to produce a P1 board in the same format too, or you could do your own that could plug in the same.

  • I was just teasin' you Peter, I know you are busy. It has been nice chatting with you though :)

    My main purpose is the demonstration of a prototype, but I personally think it is a good idea, for breadboard ad-ons, just my opinion. I think they would sell well to the newbies.
  • @idbruce and @Peter Jakacki , Yet another thread full of gold. I would have gone the way of the pot as well. Seems every time one of these threads start up, the experience and ideas just flow from the woodwork. My thanks to the both of you.
  • TY Frank
  • idbruceidbruce Posts: 6,134
    edited 2020-09-08 - 06:21:30
    Peter

    Rather than hijacking frank freedman's thread, perhaps discussing this here would be better. :)
    Now when I say an RC circuit, then that's all it is, a series resistor from a Prop I/O connected to a cap to ground. This forms a simple filter that averages the duty cycle of the high-frequency waveform so at a 25% duty cycle produces 1/4 of the 3.3V or 825mV approx. So effectively it's like a DAC. I'd use something like 1K and 0.1uF.

    In my scenario, with the overlay modules, particularly with this driver I am working on, would it be better to use the RC circuit that you suggest or should I use one of the D/A pins that these modules will have access to? In my particular situation, I am designing these modules to plug into a Propeller Activity Board WX. The Propeller Activity Board WX provides (2) access sockets for D/A and the datasheet has this to say:

    Digital to Analog access sockets — D/A 0, 1
    o Output voltage range: 0 to 3.3 V
    o D/A 0 is the digital to analog voltage from P26 after it has passed through a low-pass
    filter and buffer amplifier (but before it has passed through the coupling capacitor to the stereo output jack’s right speaker channel).
    o D/A 1 is the same as D/A 0, but the duty modulated signal is provided by P27.

    In the attached picture, the pins surrounded by the blue rectangle represent the access to these D/A sockets.

    DA%20access.jpg
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  • Yes, this is the same RC filter but it is buffered. However the vref input on the DRV8825 doesn't need buffering as it is 3ua load worst-case, so I would just pick the I/O that is most convenient and place an RC right next to the chip. You can always change the values to suit later but I can't see you having any problems with 1k and 100nF.
  • You can always change the values to suit later but I can't see you having any problems with 1k and 100nF.

    I was just wondering since they were available. Thank you. I hope you are have a good day or night, whatever time it is there :)
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