Mnemonic Password Generation Algorithm for QWERTY Keyboards

I've a "mnemonic" password generation function that goes something like this:

function Mnemonic($mnemonic)
{
    $result = null;
    $charset = array(str_split('aeiou', 1), str_split('bcdfghjklmnpqrstvwxyz', 1));

    for ($i = 1; $i <= $mnemonic; $i++)
    {
        $result .= $charset[$i % 2][array_rand($charset[$i % 2])];
    }

    return $result;
}

Basically this generates a string with $mnemonic length where every odd character is a consonant and every even character is a vowel. While I understand this reduces the password complexity it's usually much more easier to remember. Now I want to improve it by generating strings that are easy to type.

For instance, while a *nix newbie I always prefer RHEL based distributions over Debian ones, the main reason is the ease of typing yum versus the ease of typing apt[-get], just try it for yourself.

How should I implement the logic to generate strings that are easy to type on QWERTY keyboards?

You may wanna take a look at the principles used in the Dvorak keyboard,

Those principles applied in a password-generating algorithm would be:

• Letters should be typed by altering hands.
• Use easy to type combinations. Take a look at the Dvorak layout and see the common digraphs and the positions of their letters.
• Use only one letter from the bottom row, or not. Make it random!
• You can make the ratio 2 to 1 (2 letters typed by the right hand to 1 letter typed by the left hand).
• Since the ratio is 2 to 1, you're gonna have 2 consecutive letters typed by the same hand so you're gonna have to make sure they are typed from the outside of the keyboard to the inside. This principle is applied to the digraphs.

I know you said it's a QWERTY keyboard but using these principles on a QWERTY keyboard can give you some very good results, like:

ktrd,ogkdo ("typewriter" in dvorak)

kjg;g;akd;k (using only the home row)

pjedoildupsk (just a random password following the principles)

All Dvorak haters, shush it!

I hope this helps.