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  1. Thread: Uart protection

    by UhClem
    Replies
    7
    Views
    307

    Consulting "Noise Reduction Techniques in...

    Consulting "Noise Reduction Techniques in Electronic Systems" by Ott is probably in order. Or maybe not as the chapter on ESD scared me. Put it in a metal box with no connections to the outside...
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    MODBUS RTU is pretty simple. Unless you are...

    MODBUS RTU is pretty simple. Unless you are trying to reuse code written by someone else for different hardware. Then you will have to dig into that code to see if it is doing what you need it to. Is...
  3. That specification assumes that the internal IC...

    That specification assumes that the internal IC temperature is identical to that of the cold junction. You have to make sure that is true.
  4. The cold junction on that breakout is where you...

    The cold junction on that breakout is where you solder the thermocouple wires to the board. This may not be at the same temperature as the guts of the IC. Especially if it is located badly.
  5. It is absolutely vital that the MAX31850 and the...

    It is absolutely vital that the MAX31850 and the cold junction be at the same temperature. What steps have you taken to assure that?
  6. If your only problem is with the LED pin, then...

    If your only problem is with the LED pin, then the likely culprit is in the startup code. I took a quick look to see if I could spot anything but didn't.

    There is a hook to allow you to run code...
  7. Your instruction modifies memory so that should...

    Your instruction modifies memory so that should be included.

    https://www.ibiblio.org/gferg/ldp/GCC-Inline-Assembly-HOWTO.html#ss5.3
  8. The current limits on the I/O pins is steady...

    The current limits on the I/O pins is steady state so the pulsed current for driving a MOSFET is not a problem. You do want to put a resistor of 100 Ohms or so as close as possible to the FET gate to...
  9. There have been a few changes to the...

    There have been a few changes to the initialization scheme over the years. The two most significant being the SD V1 specification (update from MMC) and the V2 spec. (You might want to have a copy on...
  10. If you use the same voltage source to provide the...

    If you use the same voltage source to provide the ADC reference and the supply to the sensor (whose output is proportional to that supply), the absolute value of that supply drops out. The ADC output...
  11. If you read from a 32 bit register and end up...

    If you read from a 32 bit register and end up with extra garbage in a 64 bit value, the garbage didn't come from the 32 bit register.
  12. Replies
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    515

    Which is exactly what I was refering to with that...

    Which is exactly what I was refering to with that 1320us delay when reading data.

    Do not use that slow version of pulseEnable with its 100us delay. The whole point of checking the busy flag is so...
  13. The data sheet for the MS5611 shows separate pins...

    The data sheet for the MS5611 shows separate pins for protocol select and SPI chip select.
  14. Replies
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    515

    I know nothing about that library code. I have...

    I know nothing about that library code. I have only used character LCDs with the MSP430 and writing my own code. Various versions over the years: 4 bit, 8 bit, and with or without read.

    Before...
  15. Replies
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    515

    The resistor is there to limit fault currents...

    The resistor is there to limit fault currents when the clamp diode turns on. (5V signal to 3.3V device) Most devices list a current limit (a few mA) in their data sheet but I couldn't find one here....
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    898

    ACMD41 is not the first command sent (CMD0 and...

    ACMD41 is not the first command sent (CMD0 and CMD8 precede it) and it appears that this error code is sent if there is a timeout waiting for a response. I can't think of any reason why a card...
  17. Replies
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    1,021

    Part of that schematic fragment bugs me. While...

    Part of that schematic fragment bugs me.

    While it isn't shown as being connected to anything else, the INA169 output is connected to a capacitor rather than the required resistor. The INA169 puts...
  18. It has been a while since I have looked in this...

    It has been a while since I have looked in this particular rabbit hole, so I have forgotten most of what I learned. :-)

    Pretty much everything I learned, I learned here:...
  19. That is not an ESD clamp. It is simply there to...

    That is not an ESD clamp. It is simply there to protect against voltages which would trigger the internal parasitic SCR between Vdd and Vss. You still have to limit current through the clamping...
  20. Unused GPIOs should be set as outputs or at the...

    Unused GPIOs should be set as outputs or at the very least have their internal pull ups enabled so that they don't float. While the pins on CMOS devices will usually have clamping diodes on them...
  21. Connecting any input pin directly to something...

    Connecting any input pin directly to something which the user can touch is a bad idea. Of course I just finished reading Henry Ott's book from start to finish so that final chapter on ESD may color...
  22. Replies
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    3,225

    Microchip makes some nice FET drivers in several...

    Microchip makes some nice FET drivers in several varieties. Something like the MIC4416 should do the job.
  23. It appears that all of the ranges are multiples...

    It appears that all of the ranges are multiples of 30. So divide EncoderCount by 30 and use the result to index into a table.

    digitalWrite(30, encodertable[EncoderCount/30]);
  24. Replies
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    875

    Which suggests that there is something flaky with...

    Which suggests that there is something flaky with the pot. Since you are feeding the pot from an external supply, drop its voltage to say 2V. Does the problem occur at a proportionally lower voltage?...
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    2,277

    The time required to hold CNVH high is 10ns. It...

    The time required to hold CNVH high is 10ns. It would require an exceptionally fast micro to violate that. I would worry with a Teensy 4.1 but not with a 3.2. The conversion time of 700ns is a...
  26. Replies
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    673

    I have a can of the MG Chemical Silicone...

    I have a can of the MG Chemical Silicone Conformal Coating that I use on boards that will be exposed to corrosive environments.
  27. Replies
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    2,277

    Wait a minute, are you really expecting to get...

    Wait a minute, are you really expecting to get 1.8V out of a LM317 with 3.3V in? The minimum input to output differential is 3V.
  28. Thread: GPS and DMA

    by UhClem
    Replies
    6
    Views
    892

    DMA works best with things that provide data in...

    DMA works best with things that provide data in nice known block sizes.

    You have what is effectively a continuous stream, since the GPS is not going to wait after each 4KB, you must always be...
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    378

    If this is your first experience with RS485 I...

    If this is your first experience with RS485 I recommend digging up an old CIrcuit Cellar article titled "The Art and Science of RS485". Google usually turns up a pdf.

    One thing to watch out for is...
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    2,070

    It depends a lot on your application. I went the...

    It depends a lot on your application. I went the low level route with no file system because I needed higher write speeds.

    When writing data to an SD card you get best performance when writing in...
  31. A MPU6050 should always report 0x68. Since this...

    A MPU6050 should always report 0x68. Since this is derived from the I2C address, it should also require a change to that to get something different.

    Unless it is not a MPU6050. Some other flavor...
  32. One of the things the startup code does is read...

    One of the things the startup code does is read the WHO_AM_I register to make sure that the magic number returned is as expected. Perhaps your board is returning a different number.
  33. Replies
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    Since the SPI clock during initialization is...

    Since the SPI clock during initialization is supposed to be under 400KHz, a slow interface isn't going to be a problem at that stage.
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    1,684

    I didn't have any trouble. Figure 35 shows a...

    I didn't have any trouble. Figure 35 shows a simplified version of the input circuitry including CADIN which is the sampling capacitor with a typical value of 1.5pF. Figure 36 shows the minimum...
  35. Replies
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    1,684

    You are sampling at 50KHz so have some sort of...

    You are sampling at 50KHz so have some sort of filter with a corner frequency of less than 25KHz. The average setting causes the ADC to perform 4 conversions just as fast as it can. The samples are...
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    This is of dubious utility. Sampling a signal...

    This is of dubious utility.

    Sampling a signal four times in quick succession might help if it were the ADC that was the problem. If you have a proper pre-sample filter in place then the only...
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    Empty as in nothing driving the input at all? Of...

    Empty as in nothing driving the input at all? Of course that will be noisy.
  38. Replies
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    A charge amplifier is the usual thing to use with...

    A charge amplifier is the usual thing to use with a piezo sensor.
  39. Replies
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    3,824

    I learned a long time ago that electrons are...

    I learned a long time ago that electrons are notional little things that will go where they want to rather than where I think they should go. Details matter and schematics rarely show enough of it....
  40. Replies
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    940

    That current is required to meet all...

    That current is required to meet all specifications for that very high speed part. What is really required for your low speed application? And high impedance load? See Fig. 6 which plots output...
  41. Replies
    7
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    940

    A couple of questions: Does the optocoupler...

    A couple of questions:

    Does the optocoupler really require 10mA?

    Do you really need optical isolation? (This implies that the receiver doesn't work well with others.)
  42. If you have 100 Ohm termination resistors on each...

    If you have 100 Ohm termination resistors on each end of the cable, then driving 5V into that will require 100mA. Compared to that, everything else is small change.

    The driver will not actually...
  43. Current demand on a RS485 net is usually driven...

    Current demand on a RS485 net is usually driven by the termination resistors. The transceivers don't require enough to matter much.
  44. Replies
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    557

    I am a bit concerned with the lack of a delay...

    I am a bit concerned with the lack of a delay from requesting data to reading it. The data sheet is a bit opaque on the conversion time. To sidestep that I would reverse the order of operations in...
  45. No. The charge on a capacitor is C*V. When the...

    No. The charge on a capacitor is C*V. When the ADC samples the signal it connects the analog input to the sampling capacitor.Typical a few pF. (See data sheet for the particular value for your...
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    1,594

    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...
  47. 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:

    ...
  48. 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...
  49. 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...
  50. 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...
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