Search results

Not shown in that diagram is the connection between the ground pins of the two systems. That is important because one is generating an analog voltage with respect to its ground while the the other is measuring a voltage with respect to its ground. The two grounds might not be the same.

SD card write times can vary and with large files it gets worse. The best method for dealing with this is to separate the SD writing process from the data collection using buffers. The data collection process stores data into buffers and when a buffer is full the SD write process writes it to...

The specification has something about this. 4.13.1.7.2 (version 8 of the spec) says that the maximum FAT write time shall be less than 750ms. A little later in 4.13.1.8.2 it has a table for various speed classes. All of which show an average time of 100ms but keep that maximum of 750ms. Plus of...

Unfortunately, the SD specifications say: What triggers a license requirement? I don't know. Maybe it is hiding in one of those documents or somewhere else on the web site. But people have been writing code to these specs for a couple of decades.

I prefer to write my data logging programs differently. Data collection is driven by interrupts and the data gets packed off to a data buffer. Multiple buffers some power of two times 512 bytes in size. When a buffer is full, the foreground task notices and begins the write operation. This...

For more than you ever want to know about your sensor noise, there is Allan Variance. It does require that you collect samples at a uniform and known rate of course.

You probably want to read the SD specification as it goes into more detail. It used to be pretty simple but with each new revision of the specification it has gotten more complicated. Recording Unit size, Allocation Unit size, Erase size. But if you are writing via something with a file system...

Interrupts vary between processors. Some disable all interrupts while servicing an interrupt (MSP430 for example) others allow higher priority interrupts to horn in. It all depends. Since interrupts are for things that happen infrequently (usually) or need to be serviced quickly, it is always...

CMD6 is included in the libraries. It is used to query the card before switching the clock speed above 25MHz.

You need to read the SD specification as it has quite a bit to say about power limits. For example: "CMD6 mode 0 is used to query which functions the card supports, and to identify the maximum current/power consumption of the card under the selected functions." 200mA seems to be the limit for...

For documents, use Google or other search engine. I think you are confusing the signal requirements on the RS485 side and the micro-controller side. The RS485 side can handle voltages in excess of Vcc. See data sheet. (Common mode range: -7V to 12V) And read The Art and Science of RS485 from...

Or use one of the many MAXIM 3.3V RS485 chips.

Art and Science of RS485 from Circuit Cellar Ink magazine way back in 1999 is always a good thing to read when starting out with RS485. Google usually turns up a link or two to a copy. Some of the MAXIM chips have slightly altered input thresholds which make idle bias redundant. Although I...

The M32x16() function looks like a fixed point operation. Sort of. Works with any C compiler but is of course faster on targets with hardware multiply. Like some ARM chips. Floating point and integer multiply on the Teensy 3.6 are equally fast. Although for fixed point what I usually look for...

I never found that sort of data very useful. I prefer graphs. For my testing I wrote the current value from a hardware timer into the write buffer before issuing the write command. Then read the data back and process to find the time since the previous write command. Producing graphs like...

Maximum write speed requires writing data in RU (Recording Unit) sized blocks which are over 128KB for big SD cards. But not to worry, it has been a while but I recall looking at the code for one library (I forget which one) and rather than complete a small write would leave it open. Continuing...

Most current GPS receivers will provide data in 30 seconds. This is the time required to receive the ephemeris data. They do not need almanac data. The NMEA data strings contain the almanac data. That and the correct time will let you compute which satellites are in view. But with the current...

Many of the MAX RS485 parts have slightly altered input thresholds that should eliminate the need for bias. But it reminds me of an article I read in Circuit Cellar long ago that is always a good reference: https://www2.htw-dresden.de/~huhle/ArtScienceRS485.pdf This refers to an application note...

When you say the RX line goes low with enable line makes me suspect a particular problem. If you disable the RS485 receiver when you enable the transmitter you will have trouble unless you have something to pull up the receiver output. Which is a tri-state. No pullup and it just floats around.

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 world. It's the only safe way. :-)

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 it using the serial port you expect? Is the driver enable working? With the correct timing...

That specification assumes that the internal IC temperature is identical to that of the cold junction. You have to make sure that is true.

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.

It is absolutely vital that the MAX31850 and the cold junction be at the same temperature. What steps have you taken to assure that?

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 early, well before the code to ramp up the clock system and USB with their long delays. The catch is...

Your instruction modifies memory so that should be included. https://www.ibiblio.org/gferg/ldp/GCC-Inline-Assembly-HOWTO.html#ss5.3

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 limit its tendency to oscillate. (Because of the parasitic inductance of the wire.) For best...

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 hand: https://www.sdcard.org/downloads/pls/ It is up to V8 now.) I looked over the init code and...

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 then depends only on the sensor and not the supply voltage. Assuming a reasonably stable supply...

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.

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 you can avoid that delay. The 1us delay just before the function return is pointless. It is wildly...

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

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 writing new code, look at what you have and see if you can find the problem. With a copy of the LCD...

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. Exceed that limit and you risk latchup. There is a limit of Vdd+0.3V on inputs. You can use...

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 wouldn't respond at all to ACMD41. Unless it doesn't like the voltage range specified in the argument...

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 out a current that you have to convert to a voltage. With a capacitor I don't know how high that...

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: https://www.ibiblio.org/gferg/ldp/GCC-Inline-Assembly-HOWTO.html#ss5.3 It includes an example of using a register as both...

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 diodes. Not sure how the Vdd side gets along without the clamp. I just finished reading the second...

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 those are useless for protection against ESD. You have to provide that. (See also "The Art and...

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 my thinking a bit. The series RC filter is certainly a good idea.

Microchip makes some nice FET drivers in several varieties. Something like the MIC4416 should do the job.

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]);

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? If yes then it is definitely the pot. If it stays at 1.65V, then it might be the ADC. ADC's...

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 different story. An easy way to manage this is to lower CNV, read the data, and raise CNV. Do not...

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

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.

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 processing data. The ISR that is called when each block of DMA completes must setup for the next block...

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 the state of your serial data in pin while in transmit mode. The MAX485 floats the receiver output...

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 large, and I do mean large, blocks. (See SD specification.) There is a library around that sneaks...

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 of MPU or even a fake. (The MPU6050 is not recommended for new designs so production of the real...