Hello Forum,
for a standalone Projekt I have plased my UNO in a solid case include a battery pack and some sensors for data logging. Now I would like to use a usb pen drive as internal memory to save the data. At the end I will have access to the usb pen drive direct from the computer over a usb connector in the case with simultaneous loading of the battery pack.
It is possible to use a usb memory with parallel connection if one host is allway turn off? Do i need any backups?
What exactly are the differences between a USB host and device?
The host initiates all communication on the bus, the device only responds when asked by the host. For Details see the specs on usb.org.
When two devices connect [...]
One must behave as the host and the other as the device. Details can be found in the USB OTG Specs.
Can one device acts as a host as well as a device?
For example, many Android phones and tablets can (requires Android 3+). The "magic" is in the On-the-Go cable/adapter, which switches the phone into host mode by pulling the ID pin to GND.
To start a data logging project, the best option would be SD card via SPI communication. If the power consumption is high, the best option may be SPI flash memory, such as W25Q128.
To use USB stick the HOST / OTG function is required. There are USB Host shields, but I didn't have much advantage in using this shield, few people use it for this purpose, they are usually used to access devices like joysticks, keyboard, mouse etc.
The simplest, easiest and cheapest way to log data with Arduino is to use the Sparkfun OpenLog.
Just use Serial.print() to send data out the serial port (or use software serial and any pin), and it will produce a PC/Mac compatible file on a uSD card.