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Type: Posts; User: UhClem

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  1. 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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    Looking at the code for transferStop() what I see...

    Looking at the code for transferStop() what I see is something used to terminate a data transfer that is in progress. I don't know for sure what the intent was because nobody comments their code...
  9. Your diagram is incomplete as it doesn't show all...

    Your diagram is incomplete as it doesn't show all of the power connections. It is really easy to make a mistake and have ground current flow through your Teensy and turn traces into fuses. The Teensy...
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    Ratiometric means that the sensor output is...

    Ratiometric means that the sensor output is proportional to its excitation voltage and that the excitation voltage is identical to the ADC reference. Do that and the absolute value of the excitation...
  11. By providing power to the load cell from an...

    By providing power to the load cell from an independent supply you have to factor that supply voltage into the system calibration. This is why I prefer a ratiometric system where the sensor...
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    It sounds as though you have two ground...

    It sounds as though you have two ground connections. One for input power and another with your signal. The problem being that both are connected to the vehicle body. Creating a nice big loop to...
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    Enabled both the receiver and transmitter at the...

    Enabled both the receiver and transmitter at the same time so that you can receive what you are sending. Then compare the received packet to what was transmitted. If they are the same, there was no...
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    I have a Teensy 3.6 servicing MPU-9250 interrupts...

    I have a Teensy 3.6 servicing MPU-9250 interrupts at 32KHz. But I had to pay a lot of attention to how much time was required to transfer data. Even running the SPI port at 20MHz the timing is tight....
  15. It has been a long time since I looked at that...

    It has been a long time since I looked at that data sheet and I had completely forgotten about that footnote. Kind of unusual.

    But given that, the voltage limit of Vdd+0.3V is hard to explain. But...
  16. The pins have ESD protection diodes which can...

    The pins have ESD protection diodes which can cause trouble. Powered or not. It is entirely possible to run some micro-controllers with Vcc disconnected but drawing power from these diodes. (I have...
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    They start out identically. But in order to...

    They start out identically. But in order to switch the card into SPI mode you assert the CS pin while transmitting CMD0. SD mode (SDIO is actually a variant of SD cards) starts as 1 wire but you can...
  18. Sorry. I like the Teesy but dislike the Arduino...

    Sorry. I like the Teesy but dislike the Arduino environment. So much so that I went a different way for my logger.
  19. Why can't you do it in the ISR? Do you have...

    Why can't you do it in the ISR? Do you have something else going on that you haven't mentioned?

    While in general you do want to keep ISRs short, that is to keep from blocking other tasks. If there...
  20. Acquire the data in the ISR and store it in one...

    Acquire the data in the ISR and store it in one of many buffers. (Make the buffers at least 4KB in size and a nice power of 2.) The main routine just waits for there to be a full buffer and writes...
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    The output data rate in the ADXL345 depends on...

    The output data rate in the ADXL345 depends on its internal oscillator and the data sheet is silent on its accuracy and stability.
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    I suspect that this depends more on the software...

    I suspect that this depends more on the software (which you don't describe) than on the SD card.

    Any FAT library is going to create occasional pauses when it needs to search for a new cluster. If...
  23. Thread: Emmc

    by UhClem
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    MMC cards (and presumably eMMC) are a bit...

    MMC cards (and presumably eMMC) are a bit different and will require changes to the SD card drivers.

    I still have a 64MB MMC card gathering dust around here somewhere. I can't recall if I ever...
  24. Thread: Emmc

    by UhClem
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    The SDHC clock divisor is limited so for best...

    The SDHC clock divisor is limited so for best performance you need to carefully select the main clock. At 256MHz divide by six is the best you can do which means that the SD clock is slower than it...
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    There is a lot of code there, more than I really...

    There is a lot of code there, more than I really care to go through but a few things that jump out:

    You have no protection from writing data to a buffer after it is full. This will clobber...
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    You are doing it differently. I have a group of...

    You are doing it differently. I have a group of buffers. When one gets full, data goes into the next one. The main loop watches for a buffer to be full. When that happens, it writes the data to the...
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    It is about speed. Ideally interrupt service...

    It is about speed. Ideally interrupt service should be fast so that it doesn't hold up the rest of the code. As for calling other functions, the only problem I have noticed is the C compiler getting...
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    Yes. Writes to SD cards do that. Made worse by...

    Yes. Writes to SD cards do that. Made worse by using a FAT file system. Allocating a new cluster triggers a scan of the FAT (1 or more reads) and update. Which takes time. Dependent on the state of...
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    By writing to a lot of different files you bring...

    By writing to a lot of different files you bring the dynamics of that into play. FAT file systems have just so many entries in the initial directory table and will have to allocate more space after...
  30. I have to wonder why you are using an SPI...

    I have to wonder why you are using an SPI interface to the SD card when there is a dedicated SDHC high speed interface available.
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    According to the MPU9250 block diagram the I2C...

    According to the MPU9250 block diagram the I2C connection to the internal slave should be visible from the MPU9250 aux I2C pins. Monitoring that might give you some insight into where the problem...
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    I think you have an unrealistic expectation for...

    I think you have an unrealistic expectation for low pass filter performance.

    If you set the corner frequency to 200Hz and use a 400Hz sample rate then the attenuation will never be better than 3dB...
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    http://home.earthlink.net/~schultdw/logger/eforth....

    http://home.earthlink.net/~schultdw/logger/eforth.html
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    Which is a problem because getting the...

    Which is a problem because getting the connections correct is most of the battle. From your description it still isn't clear if the shunt is on the high or low side and just exactly how the Teensy is...
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    I dug into the data sheet and the ADC has a...

    I dug into the data sheet and the ADC has a differential input mode which is perfect for this application. I have no idea if the library code supports this hardware capability. If not, you will have...
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    I assumed that you were running 5V to the Teensy...

    I assumed that you were running 5V to the Teensy to provide power. There really is no other reason to do so since those pullups are best located with the master.
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    [QUOTE=merrillii;195183] If I removed the...

    [QUOTE=merrillii;195183] If I removed the pullups from the slave teensy then wouldn't the pullups on the master just try to supply power to the regulator in the same way? /QUOTE]

    No. The path is...
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    The data sheet claims that there are ESD...

    The data sheet claims that there are ESD protection diodes to ground only so there is no clamp to Vdd causing trouble.

    Your pullups on the disconnected slave board are odd. I2C requires just one...
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    I know that this old DATAQ serial data logger...

    I know that this old DATAQ serial data logger (DI-194R) I have can do +/-10V using a 0-5V ADC in a PIC using just resistors in its front end. This of course makes assumptions about the output...
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    The internal voltage reference output is on...

    The internal voltage reference output is on VREF_OUT and the data sheet says that the capacitor should be 100nF +/-25%. I wouldn't exceed that because it might overload the reference buffer amp.
    ...
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    MMC5883 (http://www.memsic.com/magnetic-sensors/)...

    MMC5883

    Digi-Key shows it as active with thousands in stock.
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    It also requires a new hardware interface as...

    It also requires a new hardware interface as Vddio is limited. While the chip is happy running on up to 3.6V, the interface isn't.

    For me this is a step down in capability. The maximum clock...
  43. The absolute levels of A and B don't matter...

    The absolute levels of A and B don't matter nearly as much as their difference. Capture the difference between A and B for a few data packets.

    Another option besides idle state biasing (which is...
  44. OK, it wasn't clear from your drawing but it...

    OK, it wasn't clear from your drawing but it looks like you have the RS-485 ground reference covered.

    One thing to check is the power supply. Just how much current can you get from the 12V supply?...
  45. That is a problem. Unless there is a fault...

    That is a problem.

    Unless there is a fault there is zero current in the safety grounds other than perhaps some high frequency hash from input filters on equipment. With no current and everything...
  46. The piezo isn't so much of a voltage source as it...

    The piezo isn't so much of a voltage source as it is a charge source. The usual thing to do is to include a charge amplifier which will have a low output impedance suitable for driving the ADC input.
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    I hadn't bothered with the magnetometer on the...

    I hadn't bothered with the magnetometer on the MPU-9250 since I was interested in high rate gyro data and a previous bad experience with the MPU-9150.

    When using an SPI interface with the MPU-9250...
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    I have always liked the Honeywell parts but they...

    I have always liked the Honeywell parts but they seem to have scaled back their offerings while I wasn't looking. The HMC5843 had ~1600 counts/uT but was I2C for example.I couldn't find any similar...
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    Then why did you buy the MPU-9250? The...

    Then why did you buy the MPU-9250? The magnetometer is a third party chip grafted onto the accel/gyro. (Hence the I2C.) Worse, the magnetometer is horrible. Not quite as bad as the one in the...
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    Reading the magnetometer is about the hardest...

    Reading the magnetometer is about the hardest thing to do. Start with something simpler.

    Configure the accel and gyro. Set the sample rate and such. Then get data. Which brings up the point of...
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