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  1. Looking at the startup code, I see that the code...

    Looking at the startup code, I see that the code hooked into the early_hook by default disables the device watchdog. So any replacement is going to have to do that in addition to whatever else you...
  2. 1) Disabling interrupts in addByteToTx() just...

    1) Disabling interrupts in addByteToTx() just wastes time since txB_wptr isn't modified anywhere else. Certainly not in another ISR.

    2) The more natural (and faster!) way to write that is:

    ...
  3. Since analogReadContinuous is just a fancy way to...

    Since analogReadContinuous is just a fancy way to read the ADC result register, it can't be the cause of your trouble. The ADC will keep on performing conversions in continuous mode until you stop it...
  4. Pretty much every I/O module has clock control...

    Pretty much every I/O module has clock control that must be enabled before using that module. Those bits are in the SIM_SCGCx registers. The DAC also has to be initialized with things like your...
  5. Why in the world would you serialize the data? I...

    Why in the world would you serialize the data? I could see doing it if you were short on I/O but you aren't. Even at 75MSPS that fast processor is going to be hard pressed to read and do something...
  6. Including the conversion time is a wasted effort....

    Including the conversion time is a wasted effort. The ADC requires a clock input with very low jitter which means that you know (or should know) the timing precisely. Use that clock to trigger the...
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    That 8 Ohm load on your output can't be making...

    That 8 Ohm load on your output can't be making that opamp happy.

    If all you want to do is reduce the amplitude to drive a low level input then all you need are some resistors. But make sure that...
  8. Since you only need to sink current a simple NPN...

    Since you only need to sink current a simple NPN transistor driver is sufficient and robust enough so that the Zener isn't required.
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    You didn't fix it. The only way that can have any...

    You didn't fix it. The only way that can have any hope of working is if there is a connection between the opamp ground and the ground of whatever is driving J1. Which defeats the purpose of the...
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    I am wondering how that circuit is supposed to...

    I am wondering how that circuit is supposed to work.

    The the opamp has no explicit reference for the signal it gets from J1 (MIDI-in). It might be getting it via its output which manages to have...
  11. When I look for a data sheet on the AD8225 IA,...

    When I look for a data sheet on the AD8225 IA, what I find looks nothing like your schematic. The AD8225 is a single device in an 8 pin package with fixed gain and no Rg.

    What are you really using?
  12. 220nF seems a bit small for 30Hz.

    220nF seems a bit small for 30Hz.
  13. 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.
  14. 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...
  17. 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...
  18. 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...
  19. 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,...
  20. 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...
  21. 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.
  23. 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...
  24. They are. The Teensy has some extra filtering...

    They are. The Teensy has some extra filtering between the digital and analog power pins.
  25. 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...
  28. 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...
  29. 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...
  30. 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...
  35. 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.
  36. 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.
  41. 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.
  42. 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...
  43. 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...
  44. [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. :-)
  45. 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...
  46. 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...
  47. 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...
  48. 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...
  49. 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)
    {
    ...
  50. 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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