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• Yesterday, 10:15 PM
The most straightforward way to do this is: uint32_t totalSamples = secondsToSample * SAMPLERATE; // pre-calculate number of samples needed based on duration of sampling volatile void samplesCollected =...
16 replies | 1264 view(s)
• Yesterday, 03:44 PM
It should be straightforward to log for a fixed amount of time by using an elapsedMillis timer which is reset when starting logging. In the loop you would add code to check the elapsedMillis timer and call...
16 replies | 1264 view(s)
• 03-26-2021, 12:06 AM
After working for a while with downconverting 40KHz ultrasonic signals and thinking about the timing of conversions for Pk-Pk voltage measurement, I decided that I needed a T4 frequency counter that could work with...
0 replies | 138 view(s)
• 03-25-2021, 11:36 PM
A few experiments might prove interesting-----if somewhat costly in Teensies and time: 1. Does the timing of the damage change if you change the sampling speed and conversion speed? 2. Does the timing of the...
22 replies | 1383 view(s)
• 03-24-2021, 04:05 AM
The voltage source was a signal generator with a 50-ohm output impedance. I think we need to make sure we are thinking of the same things. An accuracy of 0.01V means that the measured voltage is within 0.01V of the...
13 replies | 453 view(s)
• 03-23-2021, 07:11 PM
If the EEClick can output a signal of up to 5V, then your combination of 10-Ohm and 10KOhm resistors won't protect the Teensy. It only reduces the input voltage by one part in one thousand. To get the protection you...
2 replies | 124 view(s)
• 03-23-2021, 06:35 PM
On the basis that 100 lines of code is often worth a thousand lines of discussion, I put together a simple program to test over and under-sampling an ~300KHz sine wave and calculating the Peak-to-Peak voltage. The...
13 replies | 453 view(s)
• 03-23-2021, 05:52 AM
The ADC on the T4.0 can be set up with an aperture time of 100nSec or less. @Samsurp specified an accuracy of 0.01Volts in a 4.5 Volt signal, so a 10-bit resolution should be sufficient. I think you could set up...
13 replies | 453 view(s)
• 03-23-2021, 01:52 AM
Unless you subsample at a frequency that is an exact sub multiple of the input sine wave, you will eventually take a sample at a maximum and minimum point. The key to getting this to work is to know the frequency of...
13 replies | 453 view(s)
• 03-22-2021, 06:19 AM
The nice thing about designing systems with a few really expensive sensors is that the funding agencies don't quibble about the cost of upgrading to an MPU with more memory or better peripheral systems. It's not just...
9 replies | 860 view(s)
• 03-21-2021, 07:26 PM
The one used on the oceanographic sensors was the FP07DA103N when I last worked there in 2018. That is a 10K Ohm at 20 deg C unit. It's not in stock at DigiKey, but the 8K Ohm version is available for \$195.84 qty 1....
9 replies | 860 view(s)
• 03-20-2021, 10:50 PM
Let's look at the energy balance. Assume you want 8 gallons of water at 160F. Your cold water tap yields water at 60F. Boiling water is 212F. The boiling water is 52 degrees away from the desired temperature. ...
9 replies | 860 view(s)
• 03-20-2021, 09:01 PM
It just occurred to me that this down-conversion scheme might be a nice way to put together an ultrasonic doppler velocity sensor. I've got a handful of 40KHz ultrasonic sensors in the toolbox and lots of time between...
8 replies | 352 view(s)
• 03-20-2021, 08:51 PM
I played around with LTSpice a bit this morning and designed a 4-pole Butterworth bandpass filter with about 6dB gain from 38 to 42KHz and -40dB rejection at 19KHz and LOTS more at 60Hz. It takes a dual op amp, about 6...
8 replies | 352 view(s)
• 03-20-2021, 02:18 AM
My vague recollections that sub-sampling might do the downshifting seems to be valid. I wrote a simple program to collect ADC data at 38KHz and fed it a 40KHz sine wave from my signal generator. The sampled output...
8 replies | 352 view(s)
• 03-19-2021, 09:04 PM
I'll have to review my understanding of signal processing, but it seems you might solve this problem by under-sampling your input at 38KHz. The output may look like a 2KHz sine wave. You may need a low-pass filter on...
8 replies | 352 view(s)
• 03-02-2021, 03:13 AM
I'm not sure those are the parts I found by stepping through the DigiKey search process, but I'm strongly biased toward them. It was DigiKey that made it possible for me to start a small board production facility early...
12 replies | 545 view(s)
• 03-01-2021, 04:53 AM
The last time I played around with the ARM CMSIS FFT on the Teensy it was with the T3.6. I found that a Real FFT took about 1.02mSec for FFT1024 with a Hanning window. A friend is working over the same calculations...
5 replies | 690 view(s)
• 03-01-2021, 03:03 AM
I just transferred a solar energy evaluation program from the T3.6 that I used last summer to the T3.5. I ran into some compilation issues in MTP.h and MTP.cpp in the tests for processor type: #if...
909 replies | 72863 view(s)
• 02-26-2021, 10:09 PM
I dug out my LT1867L board and recorded a data file with all 8 channels connected to a 1.5V alkaline battery and sampled at 4000 samples/second. Data from each of the first four channels passed through an 8-pole IIR...
8 replies | 282 view(s)
• 02-26-2021, 04:50 PM
The LT1867 is a capacitive Successive Approximation ADC. The input acquisition time is a nominal 1.1 microseconds, independent of the sample rate. As noted, it is imperative to have good anti-aliasing filters at...
8 replies | 282 view(s)
• 02-26-2021, 03:53 AM
I've used an LT1867 board from another project to successfully collect data on the T3.6. Here is the part of the code that interacts with the LT1867: /**************************************************************...
8 replies | 282 view(s)
• 02-26-2021, 03:35 AM
Or you could consider using an SD File that is pre-allocated. This avoids the necessity for the file system to scan the FAT to find the next file cluster.
13 replies | 494 view(s)
• 02-24-2021, 03:46 AM
Excellent point. I've gone so far as to add a label to the silkscreen for things like SCK, MOSI, MISO, etc. etc. The vias generally take less than half the PCB area of a normal test point. Some of my smaller vias...
5 replies | 286 view(s)
• 02-24-2021, 03:40 AM
That was my thought too. A closer examination of the timing of the low-current part shows that those periods last about the same interval as the timing info shows for an average update of the ILI9341 (about 41mSec). ...
5 replies | 245 view(s)
• 02-23-2021, 07:03 PM
Been there, done that. I got past the problem at the prototype stage by finding a convenient place to cut the traces and do an "X" set of jumpers to switch the signals. I've also added pull-ups by finding a...
5 replies | 286 view(s)
• 02-23-2021, 05:46 PM
Funny you should ask! A few days ago, I had a setup to measure power consumption of the T4.1 while writing to the SD Card. The setup uses a high-side current sensor on the T4.1 power input and measures the current at...
5 replies | 245 view(s)
• 02-23-2021, 04:15 PM
I took a quick look at the GitHub repository and I will probably try implementing it later today. A few things still bother me: 1. The endpoint definitions are different between the T3 and T4 cores in usb_desc.h:...
9 replies | 394 view(s)
• 02-23-2021, 03:38 AM
In a post on this thread: https://forum.pjrc.com/threads/66265-Fastest-way-to-transfer-data-to-from-Teensy-4-0-4-1-and-Windows-10 I gave examples of python scripts and a Teensy 4.1 sketch that transferred data to...
9 replies | 394 view(s)
• 02-21-2021, 05:21 PM
FWIW, I've attached a PDF schematic from a data logger from about 12 years ago---back when 32GB SD cards were the largest available and cost \$50 to \$75 dollars each. We needed 128GB of storage, so I designed a...
909 replies | 72863 view(s)
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#### Basic Information

Biography:
building embedded systems for oceanographers since 1978
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Corvallis, OR
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travel
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Retired embedded systems engineer

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Teensy 3.6, SD Card, missing time in milliseconds Yesterday 10:15 PM
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