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  1. 220nF seems a bit small for 30Hz.

    220nF seems a bit small for 30Hz.
  2. Do you have a plot of ADC counts versus input...

    Do you have a plot of ADC counts versus input voltage? Patterns in that might suggest where the problem lies.
  3. The more typical way of doing this would be to...

    The more typical way of doing this would be to use a timer in capture mode. That way it does the pulse counting for you.
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    I used a Teensy to build a rocket data logger...

    I used a Teensy to build a rocket data logger.
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    It depends on the environment. If you are putting...

    It depends on the environment. If you are putting SD cards into the socket only at a nice safe ESD protected workbench, then no. If you are going to let any idiot do it anywhere, then yes, you need...
  6. Another possibility. If you aren't using the...

    Another possibility. If you aren't using the Arduino environment, what are you doing for startup code? The C startup can spend a fair amount of time copying data for initialized global variables and...
  7. There are some exceptions that might get...

    There are some exceptions that might get triggered and have default handlers. The default is fault_isr() which tries to print some info. You can use something else if it isn't providing the...
  8. Teensy uses the GCC compiler so all of the tools...

    Teensy uses the GCC compiler so all of the tools used for that are available including those that tell you about memory usage. (size, readelf, etc) At root a linker script (specific to each device,...
  9. No. It has no input and only output. (A sensor...

    No. It has no input and only output. (A sensor that you can't read is a poor sort of sensor.) Since the data sheet shows CS to output enable and disable times, there should be no conflict with other...
  10. Since the MAX31855 has no data input I fail to...

    Since the MAX31855 has no data input I fail to see what a tristate buffer on MOSI will do for it.

    You can run into problems with devices that use the same pins to support either I2C or SPI. These...
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    The data sheet addresses this. You add a resistor...

    The data sheet addresses this. You add a resistor to limit the fault current.
  12. As stated before, for best ADC performance you...

    As stated before, for best ADC performance you need an external ADC which you can isolate from all of the digital noise present on the MCU chip. That does make some effort to isolate the ADC system...
  13. They are. The Teensy has some extra filtering...

    They are. The Teensy has some extra filtering between the digital and analog power pins.
  14. Which ground? There is an analog ground pin...

    Which ground? There is an analog ground pin provided.
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    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...
  17. 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...
  18. 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...
  19. 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...
  24. 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.
  25. 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.
  30. 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.
  31. 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...
  32. 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...
  33. [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. :-)
  34. 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...
  35. 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...
  36. 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...
  37. 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...
  38. 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)
    {
    ...
  39. 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...
  48. 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...
  49. 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...
  50. 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.
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