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  1. I noticed something else. I connected a sensor...

    I noticed something else. I connected a sensor that I deliberately used a much longer cable so it picks up 60 Hz mains hum, you can see the 60Hz oscillation clearly. When it's misbehaving the 60Hz...
  2. Yeah I figured it would be something like that....

    Yeah I figured it would be something like that. It seems to not be consistent. It doesn't matter which two analog inputs I read simultaneously. If I get noisy signals I just have to recompile a few...
  3. Yes same configuration on both channels. The...

    Yes same configuration on both channels. The signal I showed is low pass filtered in software. It is a 1.25V DC signal from a voltage reference although you are seeing it as 0. I didn't take a...
  4. No the different speeds is a typo. I'm usig the...

    No the different speeds is a typo. I'm usig the same speeds.

    It's an SMT board which I designed to the best of my ability. I'm not dissatisfied with the noise I just want it to be consistent.
    ...
  5. I'm using a teensy 4.0. Is there a reason why I'm...

    I'm using a teensy 4.0. Is there a reason why I'm getting twice the noise if I choose to read certain combinations of analog inputs simultaneously? I'm not quite sure what's going on, I'm reading all...
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    I have now switched to using a voltage reference...

    I have now switched to using a voltage reference and I have a question about overvoltage protection.

    The op amp inputs in my circuit are protected with resistors so there should be no currents...
  7. Thanks for clearing this up. So Cas is the...

    Thanks for clearing this up.
    So Cas is the external circuit capacitance and is not part of the adc circuit?

    For some reason I didnít see Cadin, would have been much easier.

    I guess I will have...
  8. Iíve done exactly that. Iíve pretty much sweeped...

    Iíve done exactly that. Iíve pretty much sweeped the filter from 2k to 500k. What improves things drastically is filtering in software using floats and doubles. RC filter seems a waste of board...
  9. Iíve already tested an RC filter. Iím not sure if...

    Iíve already tested an RC filter. Iím not sure if itís making any difference or if itís worse. I see no point to be honest.

    Software filtering makes a huge impact indeed.
  10. Would that antialiasing filter be below half the...

    Would that antialiasing filter be below half the frequency of the sample rate for each sensor or the sample rate of each ADC? Half of 50kHz or 250kHz?

    Or would that also include the averaging for...
  11. I'll take a look at it although I'm not sure it's...

    I'll take a look at it although I'm not sure it's going to apply.

    What I really want to find out is the acquisition time of the teensy adc (how long it charges the internal capacitor) and the size...
  12. You are talking about the exact thing that the...

    You are talking about the exact thing that the youtube link above shows. They show how to calculate these things. Only problem is knowing what values to put in from the op amp and adc datasheets....
  13. Of course, I oversample and use a software filter...

    Of course, I oversample and use a software filter but it seems that averaging on the ADC settings gives better results compared to oversampling and filtering in software. This seems to me that there...
  14. I'm not sure if you or I am misunderstanding....

    I'm not sure if you or I am misunderstanding. Sampling multiple times is what the averaging setting in the ADC does, does it not? You can choose 2, 4, 8 or 16 averages I think. It is the most...
  15. Maybe I'm missing something here but say I'm...

    Maybe I'm missing something here but say I'm sampling 10 sensors at 50kHz each at 12bit. Every sample is averaged 4 times so it's actually 200kHz per sensor. 10 sensors with two adc's means each ADC...
  16. Suitable op amp for driving the teensy4 ADC

    Hello!

    I just saw this document: https://www.eetimes.com/using-op-amps-with-data-converters-part-1/#

    Part 2: https://www.eetimes.com/using-op-amps-with-data-converters-part-2/

    Part 3:...
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    The Texas Instruments manual for some reason...

    The Texas Instruments manual for some reason showed the pins from upside down view. Voltage reference is working now.

    However the problem was not the voltage reference or the circuit. Basically I...
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    Ok, so I got a voltage reference in the mail, the...

    Ok, so I got a voltage reference in the mail, the LM385Z...
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    Ok thanks. How exactly do you calculate how many...

    Ok thanks. How exactly do you calculate how many bits? I'm guessing it should be dividing the max value with the noise value and then if it's about 1024 it's 10 bits.
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    How could I see what the noise floor of the...

    How could I see what the noise floor of the teensy is and not interference from my circuit?
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    Nope, that made no noticeable difference. Neither...

    Nope, that made no noticeable difference. Neither did pulldown.

    I loaded up a fresh teensy4 without any circuit. Just sampling the empty analog pin has more noise than my circuit. Why is that.
    ...
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    I will have to test. Iím designing a new pcb with...

    I will have to test. Iím designing a new pcb with only surface mount components and itís much smaller so all loops should be smaller. Will see if there is any difference. Star grounding seems pretty...
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    When designing a PCB that the teensy4 gets...

    When designing a PCB that the teensy4 gets soldered onto, should I leave the unused pins unconnected? Iím only using the ADC pins and 3.3v/ground pins.

    I only use one ground pin and Iím not sure...
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    Yes but the piezo voltage is more like -10 to...

    Yes but the piezo voltage is more like -10 to +10v around vcc/2 so it might give me 0-3.3v i to the op amp.

    Also it seems you control the voltage swing with the resistor in series with the diodes....
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    I also found this circuit on the forum somewhere:...

    I also found this circuit on the forum somewhere: https://forum.pjrc.com/attachment.php?attachmentid=15059&d=1540923756

    Does this do the same thing? It seems to compress the signal before going...
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    Yep thats it. So it will not have a linear...

    Yep thats it. So it will not have a linear response up to 0.7v or something weird like that? Any way to control the amount of the curve? How compressed it gets?
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    Will this have a true logarithmic response from...

    Will this have a true logarithmic response from the virtual ground to the max value?
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    Iíll take a look at it when I get home. Iím on my...

    Iíll take a look at it when I get home. Iím on my phone now. Donít have a spice iphone app :)
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    Thanks. I realised that a log amp would lose the...

    Thanks. I realised that a log amp would lose the negative phase of the signal so wonít work.
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    Thanks I will read it. However I think Iím...

    Thanks I will read it. However I think Iím getting squeeky clean signals other than the idle voltage problem which is probably a limitation of the teensy reference voltage.

    I will test it when I...
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    The difference as far as I can tell is that the...

    The difference as far as I can tell is that the capacitance of the cable can mess with the low cutoff frequency with a voltage mode circuit. My cables are 20cm so not going to have an effect. I can...
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    Can anyone suggest how to modify this circuit to...

    Can anyone suggest how to modify this circuit to give me only a log response?

    http://www.audiodesignguide.com/doc/ac_logarithmic_amplifier.jpg

    Do I need 4 diodes if I donít need to switch from...
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    The only other solution I see is to make a...

    The only other solution I see is to make a logarithmic amplifier since I already have to convert the piezo signal to logarithmic in software.

    This adds a lot of complexity to the circuit but...
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    This is really disappointing. Iíve spent like a...

    This is really disappointing. Iíve spent like a year working on this project. Learning how to program from scratch and now I have to find another microcontroller.

    What other options are there that...
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    Ok, I've realised that the problem is probably...

    Ok, I've realised that the problem is probably the teensy4s internal reference voltage. If I use small resistors for the voltage divider, say 150ohm or so, the ripple disappears but there is still...
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    Can you send the attached file again? I can't...

    Can you send the attached file again? I can't click on it.

    I've been looking at those voltage reference IC's, I'm looking for a suitable one. I saw that one was rated as below the precision of a...
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    I can't see the attachment/link. Although I can...

    I can't see the attachment/link. Although I can imagine what happens. It should disappear. I guess bulk capacitors is what I need.
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    Any guidelines for the capacitor values on the op...

    Any guidelines for the capacitor values on the op amps? I was thinking a 0.1uF and a 10uF?

    I'm using digital filtering which seems to work well and gives me great signal to noise ratio. I ditched...
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    Here is a screenshot of the schematic for my...

    Here is a screenshot of the schematic for my prototype board which does not have any bypass capacitors and the virtual ground is not buffered. I used two 150ohm resistors which I realise is very low...
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    BTW, I have a ground plane on my circuit. I...

    BTW, I have a ground plane on my circuit. I noticed I have the ground plane of the circuit running under the teensy. Is that a bad idea? The teensy is raised off the board because it's soldered with...
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    This is like ten levels above my electronics...

    This is like ten levels above my electronics knowledge which is basic at best. I downloaded spice and I figured out how to run a simulation and probe the different parts of the schematic but I don't...
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    Any advice for a specific op amp for the rail...

    Any advice for a specific op amp for the rail splitter? Iím not splitting exactly at half the voltage, I want the negative part to have a bit more resolution. I can allow the positive part to clip a...
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    Clean up power supply noise Teensy 4

    Hello!

    Iím wondering what I can do to clean up the power supply noise/ripple. Iím using some piezo sensors with a virtual ground circuit. I buffer the sensors and virtual ground with op amps and...
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    Aha, well I have no clue about what it is. All I...

    Aha, well I have no clue about what it is. All I see is low frequency periodic waves. Thatís what I meant by ripple. I just made a circuit that works and just tried different things. I noticed that...
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    I'm not connected to a battery so not worried...

    I'm not connected to a battery so not worried about that.

    I'm using two resistors to create a voltage divider as a midpoint voltage reference for some piezos. I can use higher value resistors but...
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    Electrical question.

    Is it OK to plug the 3.3V to the ground pin with only about 250 ohms of resistance. Is that bad for some reason?

    Thanks.
  47. I donít think so. You need to keep track of the...

    I donít think so. You need to keep track of the time of arrival so the list is a pair consisting the value and the time of arrival. You fill in new values as they come in and remove old values when...
  48. This seems like the way to go. Itís completely...

    This seems like the way to go.

    Itís completely clear now. If the value to be inserted is bigger than max it will delete everything. I thought this would be a problem but since it is the newest...
  49. Is this the explanation to the code I posted...

    Is this the explanation to the code I posted above?
  50. Thanks but that's not what I want to do. I need...

    Thanks but that's not what I want to do. I need the biggest value in a sliding window of 250 samples (5ms). The window is moving one sample every time a new sample comes in. The example you showed is...
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