I need technical help about the use of BMP280 Digital Pressure Sensor.
My project should use up to 90 of these SPI devices on a common Microchip PIC16F1789 SPI bus.
Yes 90 of this sensor. The 90 Chip selects will be generated by 8 x 74HC154 multiplexers
to accomodate the 90 needed CS pulses. Ok.
My concerns are about the MOSI, MISO, SCK data loading.
The BMP280 shows internal pullup resistances down to 70k ohms
and 400pf capacitance loading for each BMP280.
That means, for 90 paralleled devices, around 780ohms
and .036ufd on each MOSI and SCK busses !!!
No problem with the readings of MISO (BMP280 tristated SDO) all paralleled pins,
But I think the MOSI & SCK driving lines would need some kind of buffering
to keep the data reliable to each BMP280 right ?
Using as much as 90 x BMP280 Digital Pressure Sensor on the same SPI busses..
Best reply by BSTRobin
Hello Arcenson,
As we know, the decoupling capacitor which connect with power supply have an effective decoupling radius(It's the reason we need to put the decoupling capacitor around the sensor, the closer, the better). If the decoupling capacitor distance from the sensor is too long, the capacitor will NO effect on the sensor. According to this description, I don't think the capacitance of 90 paralleled device can arrive 0.035uf(same question for resistant).
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