03-21-2017 09:07 AM
What is the maximum distance that the SPI bus can transmit and receive data from a slave sensor? It must depend on a few things like the clock frequency and types of buffer. What buffer do you recommend at the slave end?
Solved! Go to Solution.
03-22-2017 07:52 AM
Hi Peter
You may find the following links useful-
http://www.ni.com/white-paper/9119/en/
http://www.ni.com/white-paper/6975/en/
http://www.ni.com/product-documentation/7448/en/
I hope this helps!
Thanks,
Sarah
03-22-2017 09:20 AM
Okay, but I can find no discussion of how long a cable can be run between the ADC in a sensor and the USB-8451.
For example:
http://www.ti.com/lit/an/slyt441/slyt441.pdf
03-22-2017 09:32 AM
Although I can find no definite length, as you said, it will depend on multiple things, it seems that if people are using an un-shielded cable, then they start having problems around 3ft long, and shielded you can have the cable a bit longer. However this is very dependent on environment, which is why we can make no guarantees
Thanks
03-22-2017 09:48 AM
Okay Sarah, so probably safe at 0.5m. Which may be okay for some initial testing and develop a longer distance solution based on line drivers, clock feedback etc as in the TI document. The NI part could then be an FPGA card as we have many sensors.
Peter
03-28-2017 07:40 AM
Based upon the TI information: SPI running at 100KHz should have around 100 ohms series termination along with a 1nF capacitance to ground. This would imply that the desired frequency should be about:
Transmission Rate: ~ { 100 * [ 1 / (R * C) ] }
For the longest possible cable; keep to a transmission medium that has a controlled impedance matched to the R value to help control any line reflections.