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Type: Posts; User: UhClem

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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....
  3. 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...
  4. 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...
  6. 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.
  7. 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...
  8. 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...
  9. 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...
  11. 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...
  12. 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...
  18. 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...
  31. 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...
  32. 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?...
  33. 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...
  34. 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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    It is an error in the header file. Looking at the...

    It is an error in the header file. Looking at the code, it doesn't use this definition. In any case, the data sheet is correct.
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    You have to configure the MPU-9250 to buffer data...

    You have to configure the MPU-9250 to buffer data in a FIFO. Otherwise the data appears in the registers and waits to be read.

    I don't know how this library handles it but I remember what I did....
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    1) Figure out how to talk to the SPI hardware....

    1) Figure out how to talk to the SPI hardware. Configure the hardware for what you want to do.
    2) Try to read the "who am i" register on the MPU-9250. If you get the expected value you can move on...
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    If the problem is another interrupt with higher...

    If the problem is another interrupt with higher priority, change your priority. But I find it hard to believe that there is an ISR that requires 96us to execute.
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    There are two levels of delays in writing to an...

    There are two levels of delays in writing to an SD card. First there is the overhead imposed by the file system. Imagine the delays you can get when you have to allocate a new cluster. Just finding a...
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    The transmitter input does not have a voltage...

    The transmitter input does not have a voltage divider. There is a 47K to Vcc and 100K to ground. Your input signal will pull the MAX485 pin to 0V and 3.3V, more or less, and those resistors will not...
  45. Then you misunderstood. It is designed as an...

    Then you misunderstood. It is designed as an interface between the 3.3V uSD card and a 5V device. The 5V side will not work reliably with 3.3V devices. Look at the data sheet for the level shifter...
  46. I don't understand why you are using a board...

    I don't understand why you are using a board designed to shift between 5V levels from the micro-controller (the Teensy 3.2 is 3.3V) to the 3.3V levels of the uSD card.
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    Best write performance requires using the...

    Best write performance requires using the mult-block write command in RU (Recording Unit) sized chunks. For large SD cards this is quite large. (RU is a multiple of 16KB)

    When I test write speed...
  48. An eForth system...

    An eForth system
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    Shouldn't be a problem unless the file system...

    Shouldn't be a problem unless the file system causes trouble. Imagine what would happen if when allocating a new cluster it had to skip over a large group of clusters already in use.



    Write...
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    You never specify what data rate you require. ...

    You never specify what data rate you require.

    As a data point, I record at 256KB/sec with no trouble. But I skipped a file system and libraries.
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