Hi!
I'm very new to the Arduino topic and just started my research.
I was able to find that you can connect multiple hall sensors to Arduino, but I need a bit more. 48 to be exact.
I'm currently thinking about creating a chessboard which will be able to detect magnetic pieces. The hall sensors seems like a viable option in terms of cost, but not sure if it's possible.
I would be very grateful for any guidance and sorry if my question was asked or is just dumb. Thanks!
It's possible alright. You could use some kind of multiplexer or even a GPIO expander and then read out the 8x8 grid row/column-wise. This is assuming that the sensors output a reliable, conditioned digital signal (e.g. '1' for a chess piece present, '0' for no piece). Things get a little more complicated if you want to use some kind of analog sensor that needs to be read with an ADC.
Have you already selected sensors for this project?
Also, are you open to alternative sensing/detection mechanisms or do you want to stick with Hall effect sensors?
- Remember there are two versions of Hall Effect sensors.
Digital
Analog
I would consider I2C or SPI GPIO expanderes. Something like 8 MCP23008 I2C port expanders (8 pin I2C). Connect 3411 Hall switches. The MCP23008 has internal pullup resistors to take care of the open collector of the 3411. Also the pin change interrupt of the MCP23008 might be handy for detecting moves.
I haven't selected anything in particular, just looking at them at this moment.
It's not arbitrary to use hall sensors for me, just thought they would suit the most in terms of price/efficiency, since I need a lot of them, but I don't need any kind of extra-performance. I just need them to tell me if there is a magnet above them. 
Thanks for the tip, I'll look into the difference!
Thank you so much for your reply, I'll look it up!
So reed relays may work, too. I've not looked into prices and availability, but they should at least be quite simple to implement in a matrix setup.