[sdiy] Very cheap SPI pressure sensors.. anybody ??

[cheater cheater]

Forgot to describe what the PCB would look like. You have a square
area split into two rectangles. Those rectangles are two plates of a
capacitor. Above it is a solid square of metal (foil, plate, ...).
This one has no split. It's not connected anywhere. The closer it is
to the two plates below it, the more the capacitance changes.

On Fri, Mar 19, 2021 at 8:44 PM cheater cheater
<cheater00social at gmail.com> wrote:
>
> Nowadays you can do analog sensing without any sensors - just a pcb
> with capacitive sensing. Look at the xwhatsit project. That's for pc
> keyboards to type on but it could help you. All you need is a metal
> plate suspended above it and something squishy inbetween, like an
> o-ring. Cost maybe $0.02 total. You're welcome. O-ring because you
> need air between the pcb and the metal plate.
>
> Bear in mind the CS-80 aftertouch has 10 values. It's not 10 bit, it's
> 10 distinct values, essentially just over 3-bit depth.
>
> Capacitive sensing can be scanned at thousands of kilohertz. Should be
> fine for you.
>
> Essentially you have your usual diode matrix and you switch in a
> specific sensing pad, and treat it as a capacitor in an oscillating
> circuit. Then you use zero-crossing detector and a counter on your mcu
> to find out the frequency. That's going to depend on the pressure
> applied.
>
> Just make sure your clock is stable across temperatures, you don't
> want aftertouch feel changing in a cold room or when the heatwave
> hits.
>
> Good luck and have fun. This is the cheapest way to do this.
>
> On Fri, Mar 19, 2021 at 4:14 PM Jean-Pierre Desrochers
> <jpdesroc at oricom.ca> wrote:
> >
> > I'm looking for very cheap SPI pressure sensors (around $1.00 a piece or less)
> >
> > For a future project. The pressure value doesn't matter but the size and cost do.
> >
> > I will need around 90 of these sensors.
> >
> >
> >
> > For example I found this:
> >
> > BMP180 GY-68 GY68 3.3V 5V BMP-180 Temperature Pressure Sensor Module Barometric IIC I2C Interface Sensor Module Replace BMP085  $0.90CAD
> >
> > https://www.aliexpress.com/item/32832330585.html?src=google&albch=shopping&acnt=708-803-3821&isdl=y&slnk=&plac=&mtctp=&albbt=Google_7_shopping&aff_platform=google&aff_short_key=UneMJZVf&&albagn=888888&isSmbAutoCall=false&needSmbHouyi=false&albcp=7386552844&albag=80241711349&trgt=743612850714&crea=en32832330585&netw=u&device=c&albpg=743612850714&albpd=en32832330585&gclid=CjwKCAjw9MuCBhBUEiwAbDZ-7mU2hTS0J2DLxvsPsj8F40L-zV8vtApw9ds_ks1c2Qjg7dLiKgsy3RoCq-EQAvD_BwE&gclsrc=aw.ds
> >
> > But because I need 90 devices and the BMP180 is I2C and has only one address value
> > I would need somekind of multiplexer to address 90 devices (one at the time obviously).
> >
> > So.. SPI devices would fit better here.
> >
> >
> >
> > One other possibility would be to use this type:
> >
> > MPS20N0040D MPS20N0040D-D Sphygmomanometer Dip Air Pressure Sensor 0-40kPa DIP-6 For Arduino Raspb   $0.74CAD
> >
> > https://www.aliexpress.com/item/4000354356373.html?src=google&albch=shopping&acnt=708-803-3821&isdl=y&slnk=&plac=&mtctp=&albbt=Google_7_shopping&aff_platform=google&aff_short_key=UneMJZVf&&albagn=888888&isSmbAutoCall=false&needSmbHouyi=false&albcp=9604672960&albag=100679328364&trgt=296904913880&crea=en4000354356373&netw=u&device=c&albpg=296904913880&albpd=en4000354356373&gclid=CjwKCAjw9MuCBhBUEiwAbDZ-7kff0q--0F6YUo73aVqE_HAtqkRyIslFbEMRTWz7QICR2szctlC7zxoCrMUQAvD_BwE&gclsrc=aw.ds
> >
> >
> >
> > But I’ll need some analog IC to manage the output..
> >
> > Again the part’s pressure specs value do not matter.. I will manage a way to use it.
> >
> > but the size and cost do.
> >
> >
> >
> > So far the best would be a SPI equivalent of the BMP180 IC..
> >
> > Let me know if someone googled something I did not spot !
> >
> >
> >
> > JP
> >
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