I realized this circuit for serial communications with my tablet. It converts signals from the 3.3V levels and logic used in the tablet to standard RS232 for the PC or USB to RS232 interfaces. It is directly powered from the tablet’s dongle, as sown in the picture. The IC used may be MAX3232 or ST3232 or similar from other sources. Such ICs are suited for operating voltage of 3 Volts. I connected my PC to a cheap tablet based on WM8650 processors and it worked very well. Please, note that the RX and TX wires must be crossed in this application !
This is the PCB I designed for the circuit. It’s available as PDF and can be printed in 1:1 scale on transparent film (even with laser printer) for use with photosensitive copper boards.
The original 1:1 PDF can be downloaded here .