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

Wed Mar 24 18:09:34 CET 2021

I take it back, actually. You could do exactly what I propose with very
light foil suspended so it can move depending on the air. It would be
extremely, extremely cheap, and given you only really need on/off you
should be perfectly fine there.

On Sat, Mar 20, 2021 at 5:30 PM cheater cheater <cheater00social at gmail.com>
wrote:

> oh, you meant air pressure sensor... sorry... i thought you meant
> polyphonic aftertouch.
>
> On Fri, Mar 19, 2021 at 10:34 PM Jean-Pierre Desrochers <
> jpdesroc at oricom.ca> wrote:
>
>> *>**As for the option of light sensing, the assumption of freedom to
>> design, would allow you to simply have an array of LEDs directly on the top
>> and a array of sensors directly under, >mounted on boards. To me at >least,
>> using optical fibers for this purpose and placing the sensing elsewhere
>> seems like an overcomplication. Unless there's some design requirement I'm
>> not seeing*
>>
>>
>>
>> An optic based reader would look about like this:
>>
>>
>>
>>
>>
>> Notice the big horizontal LEDs bar over the row of holes in reading..
>>
>> Not very nice..
>>
>>
>>
>> On the other hand a vacuum based reader would look like the original
>> thing:
>>
>>
>>
>> The rolling mechanism will be using a DC brushless speed controlled motor
>> connected to the right gears assembly.
>>
>>
>>
>>
>> *>I would consider designing boards where you have the sensors in a row
>> on the board. You could for example have 15 sensors per board and 6 groups
>> for the target of of 90. You could >then either >have a multiplexing
>> arrangement like the one I suggested, or a microcontroller on each board
>> for local processing. *This is about the way I was thinking to do it..
>>
>> *>You could then have a physical piece (3D printed or >otherwise
>> fabricated) that fits over the board to create a chamber for each sensor.*
>>
>> Very good idea ! My first ideas were to glue very small silicon hoses
>> over each sensors
>> but a separate chamber for each sensor is much better..
>> These chambers could have a small pointing upward ‘chimney’ to insert
>> the vacuumed hoses. About like this housing:
>>
>> And by the way, this reader will have its own audio player
>> playing ‘honkytonk’ sounding notes with a MIDI output !
>>
>>
>>
>> *De :* Didrik Madheden [mailto:nitro2k01 at gmail.com]
>> *Envoyé :* 19 mars 2021 16:13
>> *À :* Jean-Pierre Desrochers
>> *Cc :* SDIY List
>> *Objet :* Re: [sdiy] Very cheap SPI pressure sensors.. anybody ??
>>
>>
>>
>> So that gives me one important piece of information: the sensors could be
>> placed in a linear pattern, as opposed to, for example, being spread out
>> and needing to be wired up individually.
>>
>>
>>
>> I would consider designing boards where you have the sensors in a row on
>> the board. You could for example have 15 sensors per board and 6 groups for
>> the target of of 90. You could then either have a multiplexing arrangement
>> like the one I suggested, or a microcontroller on each board for local
>> processing. You could then have a physical piece (3D printed or otherwise
>> fabricated) that fits over the board to create a chamber for each sensor.
>>
>>
>>
>> I'm assuming here that this is a machine that you are either designing
>> from scratch, or have relative freedom to modify. In particular that you
>> control fully what's above and below the line of notes that's currently
>> being read. But from the rest of your description I realize that this may
>> not be the case. Are you for example retrofitting an old machine, or you
>> feel that you want to be true to the original principles? Or do you just
>> want a solution that works for as cheap as possible?
>>
>>
>>
>> As for the option of light sensing, the assumption of freedom to design,
>> would allow you to simply have an array of LEDs directly on the top and a
>> array of sensors directly under, mounted on boards. To me at least, using
>> optical fibers for this purpose and placing the sensing elsewhere seems
>> like an overcomplication. Unless there's some design requirement I'm not
>> seeing...
>>
>> /Didrik
>>
>> On Fri, Mar 19, 2021, 20:27 Jean-Pierre Desrochers <jpdesroc at oricom.ca>
>> wrote:
>>
>> Good idea here Didrick !
>> But a little too complicated for my design..
>> This futur project is a piano roll scanner/player.
>> This has been a project done many times by DIYers all over the place
>> but they mostly used optical approach to read paper holes
>> (fiber optics + photo-transistors).
>> This needs a LED array bar put over the rolling paper holes rows
>> for the fiber optics holes detections,  which I don't like at all..
>> I'd like better to read the punched holes using vacuumed air
>> like antique piano did. A small vacuum pump will do that.
>> This is why I'd use pressure sensors to detect any holes
>> coming up while the paper roll is playing.
>> But I'm still looking any design possibilities.
>> I'll need around 90 sensors (SPI communications) to get the job done.
>> This will obviously need some multiplexing to access each of them.
>> Doable..
>>
>>
>> -----Message d'origine-----
>> De : Didrik Madheden [mailto:nitro2k01 at gmail.com]
>> Envoyé : 19 mars 2021 14:16
>> À : Jean-Pierre Desrochers
>> Cc : SDIY List
>> Objet : Re: [sdiy] Very cheap SPI pressure sensors.. anybody ??
>>
>> Here's an idea. It's a bit janky, and requires some extra circuitry, but
>> it might work for you. The basic idea is to use a chain of 74hc595 serial
>> to parallel shift registers to generate either a chip select or clock
>> signal. You feed in a single 0 into the shift register, which you move
>> forward one step at a time.
>>
>> In the case of a chip select signal, this selects one chip at a time.
>> To select the next chip, clock the register chain one step to forward the
>> 0 bit one step.
>>
>> In the case of a clock signal, it's a bit more complicated. But this
>> could be used to multiplex I2C. In this configuration, all the data pins
>> are commoned. (Or commoned in multiple groups if needed for signal
>> integrity.) You have a similar idea as in the example above in that a 0 bit
>> travels one step at a time. You could do this the slow way and send out the
>> full chain of bits just to flip one bit and clock the local I2C bus. Or,
>> you could do it the slightly quicker way and use the output enable of the
>> 74HC595's to clock the selected device.
>> It would work like this:
>>
>> Most bits in the register are ones. For those bits, turning the output
>> enable on or off would do nothing because you're switching between driving
>> the clock signal high, or leaving the clock signal with a pullup resistor
>> which also keeps at logic high.
>>
>> One or multiple bits are zeros. When output enable is off, that output is
>> high from the pullup that you add, or which exists on the module you use.
>> When you turn on the output enable, voilà! The clock signal for that device
>> goes low, and you have fed clocked one I2C bit. I think you can fill in the
>> rest. All the other devices will also see the data line change, but they're
>> in high impedance mode, and will not react to data without a corresponding
>> clock.
>>
>> If you are able to design a board and have it ordered from JLCPCB using
>> their PCB assembly service, you could use SPL06-007. It costs, currently,
>> $0.6622/pc in 100 quantity. There's some extra cost for the board and
>> assembly service, but that should be relatively cheap in comparison.
>>
>> To give even more precise advice, it would also help to know more about
>> the details of the project. In particular the physical arrangement of the
>> sensors. If they need to branch off from a central point using cables, if
>> the cables need to be detachable etc. If you want to discuss these things
>> closer in private, feel free to contact me off-list.
>>
>> /Didrik
>>
>> On Fri, 19 Mar 2021 at 16:14, 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=shop
>> > ping&acnt=708-803-3821&isdl=y&slnk=&plac=&mtctp=&albbt=Google_7_shoppi
>> > ng&aff_platform=google&aff_short_key=UneMJZVf&&albagn=888888&isSmbAuto
>> > Call=false&needSmbHouyi=false&albcp=7386552844&albag=80241711349&trgt=
>> > 743612850714&crea=en32832330585&netw=u&device=c&albpg=743612850714&alb
>> > pd=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=sh
>> > opping&acnt=708-803-3821&isdl=y&slnk=&plac=&mtctp=&albbt=Google_7_shop
>> > ping&aff_platform=google&aff_short_key=UneMJZVf&&albagn=888888&isSmbAu
>> > toCall=false&needSmbHouyi=false&albcp=9604672960&albag=100679328364&tr
>> > gt=296904913880&crea=en4000354356373&netw=u&device=c&albpg=29690491388
>> > 0&albpd=en4000354356373&gclid=CjwKCAjw9MuCBhBUEiwAbDZ-7kff0q--0F6YUo73
>> > aVqE_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
>> >
>> > _______________________________________________
>> > Synth-diy mailing list
>> > Synth-diy at synth-diy.org
>> > http://synth-diy.org/mailman/listinfo/synth-diy
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>>
>>
>>
>> --
>> /Didrik
>>
>> _______________________________________________
>> Synth-diy mailing list
>> Synth-diy at synth-diy.org
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>>
>
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