Help with a humidity sensor

[espruino-discuss]

Posted at 2019-04-24 by cogo33

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.

[espruino-discuss]

Posted at 2019-04-25 by @yerpj

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?

[gfwilliams]

Posted at 2019-04-25 by @gfwilliams

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: http://www.espruino.com/STM32+Peripherals

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.

[espruino-discuss]

Posted at 2019-04-25 by cogo33

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.

[espruino-discuss]

Posted at 2019-04-26 by @yerpj

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.

[gfwilliams]

Posted at 2019-04-26 by @gfwilliams

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 @yerpj 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

[espruino-discuss]

Posted at 2019-04-30 by cogo33

thank you very much :))