RGB LED Fader - Purely random colors?

I've a cct here that sequences 3 LEDs through a predetermined count using a 555 and a CD4029. The counting sequence is as such :

|LED1|LED2|LED3
----------------
1| x | |
2| | x |
3| x | x |
4| | | x
5| x | | x
6| | x | x
7| x | x | x

**broken link removed**

How can I alter this mechanism so that the counting is purely random? Someone proposed three seperate 555 sources; how would I go around implementing this? Or is there any other method of making this work?

The easiest way is to replace the circuit with a single PIC, other wise you should try looking at white noise sources like zener diodes.

You could implement a white noise generator and use the 555 to gate a spurt of pulses to the counter at intervals.

TOK

Thanks for the replies. I forgot to note that it has to be as simplified as simple. I was thinking alongst the lines of a PIC like what Nigel suggested.

I'd need 3 output pins; 1 for each color and possibly implement a hold switch to "freeze" the current color, for a total of four i/o pins. I have done some minimal work with a 16F877A (just programming and building of the circut) and if memory serves me right, it has 33 i/o pins which seems like overkill in this case.

What PIC should be sufficient to meet these needs?

The PIC12F family will do

They have 8 pins(They look like an 555 timer).

You cod go down to 6 pins but you want to have 2 pins extra in case you want to add fetures.

Hi,
If you want a true random sequence I would still use a white noise generator to clock the rtc input on the PIC. This is easier than using algorithms to generate the (pseudo)randomness.

TOK