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In this page you can find a set of useful circuits that you may need to develop your project. Most of them are designed using CadSoft EAGLE PCB and can be printend in our lab without the need of an external PCB supplier.
USB - Serial adapter
This is an FTDI FT232RL based USB - Serial adapter you can use to access serial devices (0-5V levels, NOT RS232) via a standard USB port. At one side of the circuit there is a mini-USB connector, while at the other side you can find a pin header with 6 contacts: 1 - serial RXD 2 - serial TXD 3 - GND 4 - 3.3V output from FT232RL (up to 50mA) 5 - serial level selector (3.3V / 5V) 6 - 5V output from USB connector
You must connect pin number 5 to pin number 4 (3.3V) OR to pin number 6 (5V) to select the voltage levels of the serial port. If you leave pin number 5 disconnected the adapter will not work.