What are the optimal methods for controlling specific header pins via Micro-USB?

Question

Besides buying a Raspberry Pi with GPIO, what is involved in creating a circuit board that can send data to specific pins through a micro-USB cable, as well as read from data from sensors? I am open to designing my own PCB or using low-cost I/O controllers, but my knowledge is limited in what is actually required to design these interfaces.

For example, one usage would be:

1) Read temperature from an external sensor

2) send data to Android application through micro-USB

3) if temp > 80, turn on LED on the PCB

If I want to create many of these circuit boards without spending a solid amount of money, what would be the best method?

Answer 1

There are literally hundreds of micro-controllers with a USB interface, all of which can do what you want.

Most of them have example USB software.
Some of them have built-in temperature sensors, but adding an external chip like a I²C temperature sensor is easy and also eliminates the effect of the power of the controller.

You have to develop a tiny PCB with the chip(s) on them. I found writing the USB software at the PC/Android side the most challenging.

My guess is a prototype can be made for about $100 if you do it all yourself. Production price greatly depends on the volume.Your biggest cost in 10-100 up volume will be the assembly house. I estimate the materials at that volume are between $5 and $10 per board.