Temperature measurement into USB
I think this problem is very easy to solve.

You have two ways to choose from:


UART to USB converter
Real USB with HID or CDC class


Only thing you have to do is to send some data from temperature sensor (i think, using ADC converter). You can use FTDI UART &lt;-> USB converters - and send data as normal UART signals.

Many uC's has built-in USB stack - some of PIC - also 8-bit (ex. PIC16F1459), AVR's (Atmega8U2), or 32-bit STM (like STM32F405).
USB is more complicated than UART, but you can make amazing things with it. Also - CDC USB class works as UART emulator without any additional chips.

But for this kind of operation - use UART to USB converter, if you want to do it fast.

Also - with Arduino you can do it in about 15 minutes - it has dedicated virtual Serial port.

But communication is simple here. There is another problem with this. PCB for this circuit will be big. Why? You have to find way to measure all 50 ADC channels. Only microcontrollers with many GPIO can do it without additional multiplexer IC. Another thing to do is to create some noise-preventing circuits, beacuse this amount of channel can generate it - and also - you need to prevent temperature-measurement channels from noise from microcontroller. Also to increase linearity and stability you have to do bridge excitation circuits - which will take area. If you want create 3 sensor PCB - it's very easy to do it. But 50 sensors... You have to imagine that.

What if you got small amount of ADC channels? Use analog multiplexers - but then you need more GPIO for drive multiplexer logic, and more place for new integrated circuits on your PCB. Remember - analog multiplexers aren't ideal - so one channel can affect another (you have this kind of informations in datasheet).

If you use 50 channels in your microcontroller remember about proper delay between conversion on various channels - beacuse if you change channel instantly, internal ADC capacitor will have some voltage, and this will falsify measurement value.

This problem sounds easy, but it's not as easy as we think.

Try first to do temperature meter with 4 channels.