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Thread: Sending 3-axial accelerometer data wirelessly

  1. #1
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    Sending 3-axial accelerometer data wirelessly

    Hello,

    I have a wired accelerometer (KS943B100), and its data has to be sent wirelessly (range 2-3m MAX). The sensor is connected to a NI-cDAQ and sent to a LabVIEW program.

    I sought help and told me I have to connect 3 ADCs (for 3 axes) to my sensor, an MCU (teensy or other) with a wireless module (nRF24L01P+PA+LNA), and at the other side an MCU, also with the wireless module, connected to a PC.

    I have to follow these standards: 20 000Hz Sampling rate, -30dB attenuation at half of the sampling rate.

    Does someone have any suggestions for a decent MCU?
    And ADCs?

    Thanks

  2. #2
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    The sensor has a frequency response extending to over 22 kHz

    With a sample rate of 20 kHz you will need a "brick wall" 10 kHz low pass filter between the sensor and the ADC. Otherwise the data could be hopelessly aliased.

    What do you have in mind for that LPF? What bit depth does your application require?

  3. #3
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    Anti-Aliasing Low Pass Filter

    Quote Originally Posted by jremington View Post
    The sensor has a frequency response extending to over 22 kHz

    With a sample rate of 20 kHz you will need a "brick wall" 10 kHz low pass filter between the sensor and the ADC. Otherwise the data could be hopelessly aliased.

    What do you have in mind for that LPF? What bit depth does your application require?

    Yes, it's mentioned also in the norm that I do need an aliasing filter of half the sampling frequency.

    But in fact, I don't have any idea about how to choose a good Filter, nor a good ADC.

  4. #4
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    If you don't have specific requirements, forum members can't offer informed advice.

    I suggest to start with the ADC built into any of the Teensies and determine whether that is satisfactory.

    If you sample at a frequency higher than 44 kHz, you don't need the input low pass filter. Then, if necessary, apply a digital low pass filter to the samples and decimate the output to a lower frequency range.

  5. #5
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    If the requirements are exactly that, 20kSPS, -30dB at 10kHz, then it does not need to have a brickwall filter. Note, no requirements for the passband quality, so even a RC filter with suitable values would do... a crappy job, but meets the given specs. A common RLC filter arrangement would naturally do a less crappy job, e.g. a 3rd order Butterworth, etc.

    20kHz at the noise levels of such sensors should be doable also with a single (optionally simultaneous sampling) multi-channel ADC.

  6. #6
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    Thank you for your replies.

    I think teensy 4.1 should do the job of the transmitter MCU.

    1) Do I need special connectors to connect my sensor? IEPE output, BNC connectors.

    2) I want the second MCU (Receiver) to act as the sensor to the cDAQ. Is there a serial connection for teensy?

    3) Do I build my own filter or there are already built ones?

    Thank you

  7. #7
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    1) You may need a particular connector for the sensor. Check the sensor data sheet.

    2) The Teensy 4.1 has 8 hardware serial ports.

    3) You will probably need to build your own filter. So far, you have not provided enough information on the filter characteristics to make sensible design recommendations.

    For 2-3 m distance, why do you think you need a wireless connection and another MCU? Consider using wires. But if you do require wireless transmission, a UART serial radio module is much easier to use the the NRF24L01.

  8. #8
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    Thanks for replying

    1) This is the Binder connector attached pic (1). You think I can find a connector between the binder 711 and teensy ? or I need to cut it and connect directly ( What about noise )
    Attachment 24511

    2) I noticed that the serial input of my DAQ is A VGA (DE-15) connector, is there a problem or it's the same as serial ?

    3) The frequency response is from 20Hz to 1000Hz, I should use an ADC having a minimum of 20KHz sampling, and the filter should be used with amplitude attenuation of at least 30dB at the half of sampling frequency (minimum 10KHz). In the norm, these are only the specification required.

    I'm in an internship whose objective is to transform the already built, wired system into wireless. It's because of the life span of the wire.
    Second, is there UART serial radio module but with DVI/VGA connector? The picture of the connector is attached (2).
    Attachment 24510

  9. #9
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    You will most likely need to wire up the connectors yourself. Buy them from distributors like DigiKey, Mouser, etc.

    The UART serial radio modules I have in mind do not come with connectors, for example the HC-12:
    https://www.allaboutcircuits.com/pro...ceiver-module/

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