BME280 SPI maximum capacitive and inductive load

[honoju]

Hello,

Does anyone know if there is a maximum capacitive/inductive load for the BME280 SPI protocol?

In the datasheet SPI timings table (capture in attachments), they mention 25pF as a usage condition for SDO but I am not sure if it is the maximum capacitive load for the BME280

Thanks

[Jet]

Hi Sir:

Could you tell me why you want to know BME280 SPI maximum capacitive and inductive load ? Communication failed?

25pF as a usage condition for SDO out delay is minimum condition, but  when we use SPI connection, atually we don't need to connect a 25pf capacity.

[honoju]

Hello,

Thanks for your reply

Well, I'm having trouble transmitting BME280 measurement data over 1m long cables and I suspect it is the capacitive and inductive loads the cables  present to the sensor that is problematic. The transmission works well when I use small jumper wires (few cm long).

Depending on the distance between the cables (Vcc, GND, SDI, SCK, CS and SDO), I am sometimes getting only temperature and pressure data but not the humidity data and other times I am getting none of the three measurements.

[Jet]

Hi Sir:

I think it is too long distance between sensor and host by using over 1m long cables to transmit and receive data, it is easy to be interfered and lead to the signal quality unstable.

Maybe you need to shorten this distance.

Or you might try to add a resistance close to host between them to form impedance matching circuit and then observe the results.

[honoju]

Hello Jet,

I am going to try impedance matching

Thanks for your reply