What you need is natural source of random. I have used clocking higher speed quarz generator with lower speed (10 x is ok ) unstable frequency oscillator and then taken parity of the result (4-5 bits is enough for most situations, depends of cource on distribution of LF generator values) . Variable Freq. oscillator is RC and higher quarz. Now as we are not willing to give up card slot (and PCB board area ands so on ) for just RND generator maybe it is good to find existing source of random in PC itself. So - do we have RC generator in PC? YES. We have 4 of them, to be exact. Most of us do not make much use of these ports, because most games do not support them correctly. But anyhow, joystick ports are there. IO card costs 10$ if you have not already got one. So I propose scheme for PC RND generator: 1. Make LF generator using Joystick ports 2. Use HF oscilltor of PC clock ( Program Execution, if any interrupts occur, it is no problem). 3. Find out the distribution of LF oscillator and calculate the needed Parity filter size. ( By parity filter I concider parity values of N last bits) 4. Use it