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  1. How cheap? Compare them to the Analog Devices...

    How cheap? Compare them to the Analog Devices eval board paying particular attention to the power supplies.
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    It depends on the power supplies. If both have...

    It depends on the power supplies. If both have their power output returns connected to safety ground then some of that LED current is going to want to take the route of your ground connection between...
  3. First dig up a copy of "The Art and Science of...

    First dig up a copy of "The Art and Science of RS-485" which appeared in Circuit Cellar Magazine some time ago. A pdf usually turns up in a Google search. 200 feet is fairly short for RS-485 although...
  4. The SDFAT code that I have looked at doesn't...

    The SDFAT code that I have looked at doesn't disable interrupts. At least at the SD interface level. I can't think of any good reason to disable them in any case.

    For a parallel interface I would...
  5. It depends on the library. On the 3.6 I can write...

    It depends on the library. On the 3.6 I can write about the same amount of data (and more) using my own interrupt driven code. (Warning: I use Forth rather than C.) I use the SDHC DMA system while...
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    Some information is missing: 1) Is there a common...

    Some information is missing: 1) Is there a common ground connection that you didn't mention? 2) What about pullup resistors?
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    The Arduino style pin names A0- map to Teensy...

    The Arduino style pin names A0- map to Teensy ports in strange ways. From the schematic they appear spread across all of the GPIO ports. Certainly not all on GPIOC.
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    I am not the person to answer any questions on...

    I am not the person to answer any questions on the Teensy libraries. I skipped those and programmed the hardware directly in Forth. So I have a fair understanding of how the SD interface works (I...
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    The card data in version 2 appears to be from the...

    The card data in version 2 appears to be from the CID and CSD registers. These registers are read using just the CLK and CMD signal lines. Reading actual card data on the other hand requires the DAT...
  10. I am reminded of an old DATAQ DI-194 data...

    I am reminded of an old DATAQ DI-194 data acquisition system I have. It used an ADC with a 0-5V input range but had a resistor input network that let it measure -10 to +10V.
  11. If you write that as: v33 =(analogRead(A8) *...

    If you write that as: v33 =(analogRead(A8) * (3.3 / 1023.0));

    You get the same result but let the compiler combine the constants saving a floating point op at run time.

    I would be very...
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    I looked at what the SD specification has to say...

    I looked at what the SD specification has to say about CMD6 again. Very confusing.

    When asking about capabilities (mode=0) it says to select a function. This seemed useless but further reading...
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    I think you should wait for command complete...

    I think you should wait for command complete after calling SDHC_Read(). The transfer should be complete when it returns.

    I switch to 4 bit mode before checking for 50MHz capability.
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    It has been some time since I wrote this so my...

    It has been some time since I wrote this so my memory has faded a bit. Looking at the code, DSADDR is set to point to a buffer, BLKATTR is set (count=1 and size=64), and the XFERTYP flags are...
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    I use the high speed mode on a 3.6 with o trouble...

    I use the high speed mode on a 3.6 with o trouble but my code is in Forth. It is quite straightforward though.
  16. The TO220 was just an example. You will have to...

    The TO220 was just an example. You will have to do the analysis because I have no clue what your design requirements are.
  17. The measured resistance between the 3.3V net and...

    The measured resistance between the 3.3V net and ground would be infinite it there was noting connected between them. But everything is connected between them. The only thing on the 5V net is a...
  18. The pullups connected to a 3.3V supply external...

    The pullups connected to a 3.3V supply external to the Teensy are unlikely to be a problem especially if the 5V and 3.3V are always present at the same time.

    You have a lot of vias connecting the...
  19. [QUOTE=MarkT;250017]The pass by reference is...

    [QUOTE=MarkT;250017]The pass by reference is needed for the function to return its results I beleve./QUOTE]

    Pass by reference is new one for me. It sure ain't K&R. :-)
  20. Your parameter declarations are very odd. I have...

    Your parameter declarations are very odd. I have never heard of a type "int &". ("int *" yes) Especially since your are not passing anything that looks like an address or dereferencing the pointer in...
  21. The problem is power related and since you are...

    The problem is power related and since you are connecting several things together, I have to wonder about power distribution. Best is a star configuration where every device gets a dedicated wire...
  22. The 0xff being sent while reading a register is...

    The 0xff being sent while reading a register is just a place holder. You have to send something in order to generate clocks but it matters little what is sent. Because of the start bit like behaviour...
  23. The (reg & 0x3f) is there out of pure paranoia to...

    The (reg & 0x3f) is there out of pure paranoia to make sure that reg is within range. This is then OR'd with the required values for WEN and R/W which happen to be zeros to write a register. The...
  24. Look at the description of the WEN bit of the...

    Look at the description of the WEN bit of the communications register on page 79.

    You might try something like this:


    void AD7124_write(unsigned char reg,unsigned char data)
    {
    ...
  25. First of all I don't see how you are sending...

    First of all I don't see how you are sending eight bytes worth of 0xff. Second of all when you uses CS you should never ever have to do this.

    According to what I read in the data sheet each...
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    A couple but they might confuse more than they...

    A couple but they might confuse more than they help. The first is something I wrote long ago for the SparkFun Logomatic. Straight up C and Arduino libraries nowhere to be found. My effort for the...
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    The SD specification shows a maximum FAT write...

    The SD specification shows a maximum FAT write time which can be up to 750ms. This is the time to update both copies of the FAT and the directory entry. Each of which probably requires a...
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    Open and close each file exactly once. If you...

    Open and close each file exactly once. If you want to make sure data is being written, use flush. Not too often as it can be really slow.
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    The data sheet shows an absolute maximum voltage...

    The data sheet shows an absolute maximum voltage on the I/O pins of OVdd+0.3V. With the USB supply pulled it is easy for external circuits to exceed that. Normally I wouldn't worry about I2C because...
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    There is always noise. The command to read the...

    There is always noise.

    The command to read the data registers will always return the value currently stored there even if it hasn't been updated in a long time. If the ODR is 400 and you read it...
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    All of the configuration details are hidden in...

    All of the configuration details are hidden in the library (not shown here) so I have no idea what it is doing. Things like the default ODR.

    With a serial data rate of 115Kbps you are not going to...
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    My code...

    My code isn't likely to help you much. Being very much a non-Arduino Forth sort of thing.
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    I2C is a bit slow for high data rates so SPI is...

    I2C is a bit slow for high data rates so SPI is the way to go. Also, the MPU9250 allows for higher SPI clock speeds when accessing just the data registers so check that out for your particular...
  34. Since the upper 16 bits are always zero, anything...

    Since the upper 16 bits are always zero, anything exceeding that is most likely the result of your processing.

    I looked at your original post again and realized that in your data plot you were...
  35. Kind of missing my point. Which was to find out...

    Kind of missing my point. Which was to find out what the bus clock is and set the ADC clock divider appropriately. (I am not an Arduino kind of guy so I have no idea if you used the analog library...
  36. It is in the device data sheet, which I grabbed...

    It is in the device data sheet, which I grabbed before I started. Most people use the library code and let it worry about such things.
  37. I can't tell if your ADC clock is in the required...

    I can't tell if your ADC clock is in the required range of 2Mhz to 12MHz but it appears that you are using the bus clock which typically runs much faster than that.
  38. The optimizer already does this.

    The optimizer already does this.
  39. Power while awake will depend mostly on your...

    Power while awake will depend mostly on your chosen clock rate so keep it it as slow as possible. If you really be asleep for only 75% of the time then the sleeping current draw doesn't matter as...
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    Differential input voltage range is VREFL to...

    Differential input voltage range is VREFL to 31/32 * VREFH. (table 31) The voltage limits for each pin are of course -0.3V to Vdd+0.3V.

    Note that while the voltage with respect to ground is always...
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    Use the existing 1024 point FFT on the 2KHz...

    Use the existing 1024 point FFT on the 2KHz bandwidth data to find the 50Hz band of interest. Then perform a frequency shift (like an analog mixer) to move that down closer to DC. Perhaps centered on...
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    There are fairly cheap ways to get into HF....

    There are fairly cheap ways to get into HF. https://www.hfsignals.com/

    Which is probably what I would do if I ever bothered to take the General test. Or perhaps even before since Tech does let me...
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    You still haven't mentioned a sample rate....

    You still haven't mentioned a sample rate. Assuming it is far above Nyquist you can decimate the data to reduce the sample rate. (Low pass filter to remove frequencies above the new Nyquist frequency...
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    FFT frequency resolution depends on sample rate...

    FFT frequency resolution depends on sample rate and number of samples. More samples gives higher resolution.
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    There are lots of ways to buffer the data. Here...

    There are lots of ways to buffer the data. Here is something I did long ago. The data is captured in an interrupt service routine while the foreground task just waits for there to be a full buffer...
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    It has been a while since I wrote that code and I...

    It has been a while since I wrote that code and I missed where I set A12EN which causes the hardware to do an auto CMD12 when the DMA finishes.

    Something that I find peculiar about transferStop()...
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    I do see that resetting the data path engine...

    I do see that resetting the data path engine (RSTD) is recommended when recovering from an error. I have never had to do that but I use the DMA system so perhaps that is something peculiar to the...
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    CMD12 isn't required to terminate multi-sector...

    CMD12 isn't required to terminate multi-sector I/O. I have written a couple of bare metal implementations for the 3.6 (C and Forth). Both do multi-sector writes and neither uses CMD12.
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    transferStop resets the SDHC data path (...

    transferStop resets the SDHC data path ( SDHC_SYSCTL |= SDHC_SYSCTL_RSTD;) which is not required for multi block transfers.
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    Is that better or worse than shutting down the...

    Is that better or worse than shutting down the clock? (SIM_SCGC3 &= ~SIM_SCGC3_SDHC;)

    I find your concern about using writes of less than 512 bytes of data very odd considering that I see at least...
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