Help with a humidity sensor

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  • I need to read a humidity sensor whose output is given in Hz, but the values are higher than 10KHz and below 20KHz, I would like to know the most appropriate way to do this value measurement with a STM32F4 discovery. All I want is to print the frequency on the IDE console or a hypertherminal.

  • Are you sure that the humidity sensor outputs some values in [Hz] ? This seems very unlikely. Unless you talk about the frequency of sampling? In that case, you won't find easily any humidity sensor able to output new sample at more than a few [Hz]. Humidity is something that does not vary quickly.
    Could you explain in details what you want to do? Could you also share the documentation of your humidity sensor?

  • If you want to measure the frequency of a signal that fast then you're probably best off using the hardware that's built into the STM32F4.

    There's a page on how to do that here:­s

    It pretty much walks you through all the code you need to use the hardware to count the amount of times the pin changes state - then you could just sample and reset that register every second using setInterval and you've got yourself a frequency measurement in Hz.

  • Thanks to the support, this humidity sensor was developed in my teacher's lab, it is a capacitive circuit board with a conditioning circuit that contains an IC 555. It has a 5V power cable, a ground and an out, whose the values are given in frequency.
    I got satisfactory results with the oscilloscope but the desire to get this data with the espruino.

  • Thanks for the details.
    As a first try you can use the setWatch function. When the given callback is called, the parameters lastTime and time are passed to it. by doing 1/(time-lastTime) you get the frequency value.
    The limitation could be the processing time of the callback, but you can go up to 1kHz easily as far as I remember. Then you can maybe adjust the RC constant of your 555 circuit in order to decrease the maximal output frequency.

  • Yep - setWatch is nice and easy (and accurate on STM32F4), but being JS execution is slowish you'll struggle at much above 1kHz - but as @Jean-Philippe_Rey points out you may be able to modify your circuit to lower the frequency.

    The link I posted above should be pretty much copy/paste and will give you nice accurate results for the higher frequencies though

  • thank you very much :))

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Help with a humidity sensor

Posted by Avatar for cogo33 @cogo33