I tried making a text layer with a row of zeros, adding a Wiggly selector and setting the Character Offset to 1, but this caused the numbers to switch between 0,1 and 9.
EDIT: As explained in the Creative Cow post mentioned above, you need to change the Min Amount value from -100 to 0 for this to work.
Alternatively, here's an expression you can apply to a text layer's Source Text property:
Code:
framesPerSecond = 25;
numberOfCharacters = 10;
posterizeTime(framesPerSecond);
result = "";
for (x=1; x <= numberOfCharacters; x++) {
result += Math.round(random(0,1));
}
result;