SPI distance limitation (and scanning of 264 sensors)

Projects Networking, Protocols, and Devices
1

Hi,

I want to scan 88 keys on a piano with photosensitive sensors and was thinking of using either shift registers (74hc165 and hc595) or port expanders (mcp23s17).

Actually I need to scan a total of 3 x 88 = 264 sensors. Each key uses 3 sensors. 2 sensors to measure velocity and 1 sensor to determine whether a key is being kept pressed down.

I need a fast bus and thought about SPI. However I've read that the SPI distance limitation is about 10-20cm ?

Can it work, given that the 88 keys are spread over a distance of 1.5m.

Thanks,
Joël

2

I don't think SPI is suitable for this. It is intended to connect to another microprocessor - not to a photo-transistor.

But maybe you are thinking of having multiple Arduinos reading the sensors and sending the data to a master using SPI

...R

3

Both, the shift registers and the port expanders, can operate under SPI. The photo-transisters will connect to those.

4

js-:
Both, the shift registers and the port expanders, can operate under SPI. The photo-transisters will connect to those.

Doesn't that solve your problem? Locate the port expander or shift register within working range for the SPI bus.

In any case the SPI bus may work perfectly well over 1.5 metres - try it.

...R

5

Thanks, I wasn't sure.

6

js-:
Thanks, I wasn't sure.

Neither am I.

...R