# A/D Beginner Question

I want to just get an idea about the complexity of a hobby project before getting started on it.

I want to use a sensor that outputs an analog voltage. However, I want to use an A/D convertor to convert this into a digital value and then feed this into a PC via USB. The analog voltage is between -5V to +5V.

I would really appreciate any links/guidance in what I need to read more about? I'd be happy to clarify anything?

A second question would be that if I need to provide power to the sensor, what circuitry should I be looking into?

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BTW, there are plenty of cheap boards with microcontrollers with integrated ADCs and a full USB interface that you can use for a projhect like this. I'm partial to the Teensy myself (pjrc.com/teensy). –  drxzcl Jul 13 '12 at 8:32
Thanks drxzcl, I'll look deeper into the Teensy board ... –  c0d3rz Jul 13 '12 at 17:12

All you need is a resistor divider:

If Vin = +5 V then Vout will also be +5 V. If Vin = -5 V then the divider will set the output voltage nicely halfway between the two voltages, so that will be 0 V. So this scales [-5V, +5V] to [0V, +5V] for your ADC.

To get the data in your PC you'll need a microcontroller with USB on-board, or a UART-to-USB bridge like this one. If you install FTDI's virtual COM driver on your PC the USB connection will serve as a transport channel for UART data.

edit
If your sensor only needs a few mA you can use this charge pump converter to generate the -5 V from the +5 V USB supply:

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Optionally throw in a couple of clamping diodes to protect the ADC and a small/cheap Arduino to provide the ADC to USB conversion to complete a perfect little beginners hobby project. –  jippie Jul 13 '12 at 7:54
Thanks Steven that was very helpful ! –  c0d3rz Jul 13 '12 at 17:21
@cod3rz - Glad to be of help. HANWE! –  stevenvh Jul 13 '12 at 17:22