[sdiy] Very cheap SPI pressure sensors.. a possible sensor..

Jean-Pierre Desrochers jpdesroc at oricom.ca
Sat Mar 20 15:33:02 CET 2021

This BMP280 sensor board is available fo$0.49CAD at aliexpress..
Here is the possible way to use this:

You see the 2 screw holes ? I could solder a ‘L’ shaped 1/8” brass or copper tube
on each of these holes on the other side of this pcb. 1/8” brass tubes are cheap !
The first tube would be the vacuum ‘intake’ and the other tube the vacuum out.
I would just have to make a air tight chamber around the sensor
and both of these holes using hot glue or whatever.. 
The chamber would have both vacuum holes and the sensor. 
The 1/8” tubes will accept flexible silicon tubings coming
from each of the paper holes reader (fixed brass bar)
The 6 pcb pins would be left untouched to be soldered
on a motherboard (array of 32 of these 6 pins headers).
This motherboard would accommodate 2 x 74HC154 multiplexers
to address up to 32 SPI devices.

For 90 devices to be read 3 motherboard used.


But that’s just a possibility..








>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 !


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