Maximum number of devices used in daisy chained spi configuration

[ardentuser]

Hi guys! I wish to connect 10 rfid pn532 readers with arduino uno rev3 for building reader system. Is it plausible to use the multiple daisy chained spi configuration for communication? Please let me know.

[pylon]

@ardentuser

Is it plausible to use the multiple daisy chained spi configuration for communication?

It's theoretically possible but not plausible for your case because you will most probably run over the limit of the bus length (about 50cm). I don't see a use case for 10 RFID readers all within half a meter of as they most probably will interfere with each other.

[horace]

suggest a daisy chain RS485 bus - can be up to 1000metres in length

[johnwasser]

@ardentuser

Is it plausible to use the multiple daisy chained spi configuration for communication?

Depends on what you mean by "daisy chained". If you mean the output of one device going into the input of the next, that only works with simple shift registers. For more complex devices, they have to be in parallel on COPI, CIPO, and SCLK and have a separate "Select" pin for each.

[DrDiettrich]

@johnwasser

If you mean the output of one device going into the input of the next

then this will mean that you always have to request the data from all chained devices in one go. That may make sense if the devices do not require initialization nor commands and are always ready to transmit data.

[ardentuser]

Thanks @pylon for the clarification. I am proceeding with the i2c mode. With i2c configuration,I can connect 10 RFID devices right. With ther be any issues with that? Should i utilise any multiplexers or shield?

[horace]

@ardentuser

I am proceeding with the i2c mode

I2C or IIC as its name Inter-Integrated Circuit implies was designed for communications on PCBs and local inter board communications.
not recommended for cable lengths over a few metres

[ardentuser]

All the peripheral devices are within short distance (i.e. next to each other).Hence distance does not matters here. @horace

[TomGeorge]

Hi, @ardentuser
Welcome to the forum.

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Can you please tell us the application?
Why do you need 10 RFID readers for a start?

If we know your project better we can possibly offer a better solution.

Thanks.. Tom..

[horace]

@ardentuser

All the peripheral devices are within short distanc

I thought the project was a building reader system using 10 rfid devices

[johnwasser]

@ardentuser

With i2c configuration,I can connect 10 RFID devices right.

If you can set the I2C address on the RFID reader to more than 10 options or you add I2C multiplexers to give you multiple I2C busses.

[pylon]

@ardentuser

All the peripheral devices are within short distance (i.e. next to each other).Hence distance does not matters here.

That's the complete bus. So the devices must be within 10-20 cm between them.
You can extend that with I2C extender chips but that get complex father quickly.

I agree with TomGeorge: Tell us what you're trying to do. The way you think it should be done might be a dead end.