I want to use the usb cable that comes with the nokia n800 to read a simple analog input. All I'm interested in is the voltage value from my signal. I should be able to put the nokia in host mode, hook up the miniusb-usb adapter to the nokia, and feed in the analog signal to one of the usb's data pins.

I need to collect that voltage reading multiple times, so I want to be able to poll the usb port from the maemo os. Is there an API that can help me with this? Any info on how to code the n800 to collect info from the usb port in host mode would be very helpful.

Ummmm..... what? You can't read the analog value of a voltage on the USB port. No, really.

You might be thinking of the microphone port (on the headphone plug). Easier, but I don't know the DC characteristics.

Myself, I'd use an Arduino as a USB-connected A/D converter, or some other dedicated peripheral.

Oh wow I'm dumb, of course I cant read analog signal directly from the usb port. I do have an arduino board that works as an ADC, but if i wanted to use it I'd have to modify the software to work in the maemo os right? I know arduino software is supported under some linux distributions currently, but not maemo explicitly.

Shouldn't be too difficult to get the Arduino software running on the tablet, just compile and go; generally if it works on Linux it'll work on Maemo for low level stuff like that. I've compiled the Phidgets libraries for Maemo before and used those to connect to a USB Phidget to play around with, so it's definitely possible to get extra sensors/etc connected to the tablet; just keep in mind that battery life on the tablet goes out the window as soon as you start running in host mode for too long.

The other alternative is to go USB->serial adapter and use some basic serial sensor/whatever; I've used USB->serial to drive relay boards/etc before from the tablet, but never tried to do analog voltage sensing, so not sure what's involved in that.

It's actually not very hard. See my page http://www.ece.mcgill.ca/~jthiem/projects.html for a simple control-LED-on-Arduino using python and pyserial. This is all you need as a framework to read analog values.

1. You need to have a modified kernel to enable the USB-to-serial chip on the Arduino (assuming you have the USB Arduino). For the N800, I put a kernel on my website.

2. You need some way to read from the serial port in whatever language you want to write your app on the N8x0. In python, pyserial makes this very easy.

3. On a windows or linux box, write Arduino code that consists of a simple loop: read analog pin, write result to serial port. Something like this (off the top off my head, no guarantee it'll work)

void setup()
{
Serial.begin(9600);
}
void loop()
{
int V;
V = analogRead(0); // reading from analog pin 0
Serial.println(V);
delay(10); // short delay, 10ms
}

Compile load and test the code on your desktop, then connect the Arduino to the N800.

4. Write code on N800 in python to read numbers off serial port (/dev/ttyUSB0, I think) and... do something :-)

Have fun!

Joe.