Read digital data directly from a USB port

Question

I use Arduino for comunication between sensors and my C# application using a serial port. Is there any possibility to access digital components directly such as Force Sensitive Resistor - Square, from a USB port?

Do I have to write a driver for that?

I drew a semi-schematic diagram to exemplify:

Answer 1

There isn't a way to directly read an analog sensor over USB since it's a digital bus. You need some sort of processing to convert the analog signal to digital and communicate over the bus properly.

Answer 2

In order to sample information from any sensor, you will need an intermediary. The Arduino uses an FTDI chip to convert UART (Serial) to USB. When you read data over this connection, you are reading it over the Serial over USB interface. My recommendation is to stick with using the Arduino or other micro controller.

If you are really bent on reading it Directly over USB (instead of through the Serial over USB converter) you would have to implement some sort of protocol in a device that supports USB such as the Stellaris Launchpad or an Atmega32U4 AKA Arduino Lenardo. You would also have to write a driver to describe how to communicate with this USB device. Unless you were able to implement it as an already known device such as a keyboard or serial port (Yep, we went full circle there).

In short, there's no already made chip that converts Analog (or Digital) values from a sensor into something any OS would natively understand. Since USB is a protocol much like IP, you're not going to be able to use discreet devices. You're going to have to use a micro-controller with a USB stack.

Again, my advice would be to pass the sensor values over USB through the existing Serial (over USB) port. This is pretty straight forward and easily reproducible without an entire Arduino.

Answer 3

From the looks of the force-sensitive resistor, this is an analog component; the resistance and capacitance changes with the force applied to the sensor. If you check out the FSR installation guide document there are suggested electrical interfaces starting on page 16.

I would recommend the first circuit, connect Vout to an analog input on the Arduino. From there you will need to convert from ADC counts to voltages and then use a lookup table function in the Arduino to convert from voltage to force according to Figure 9. At this point you have a variable containing the force applied to the sensor. From here you can transmit the value over the USB serial bus just like any other value. Your C# application then needs to read the serial data, and parse out the value.