Hi,
i said a usb keypad because i already have 1 but i have some money and could a wire per number type of keypad.
If you are prepared to "ruin" the keyboard, it could probably be used, by accessing each key/switch in the matrix separately, but I would think a "loose" keypad would be quite cheap (and then you keep the USB keypad functional
)
The keyboards with all contacts separate might be the easiest to use, when you don't wanna use a microcontroller, but go for whatever is the cheapest.
(You could even wire up some of the small PCB switches from a discarded VHS or similar, to make your own keypad).
i will not be using a computer and would hope to not use a microcontroller ( i dont have one)
If you have no previous experience with microcontrollers (which would be an easy solution otherwise), discrete logic can be used.
The net is full of circuits for that, but some of them are quite large and you really don't need that much for a basic keypad lock.
There's basically two ways to tap in a code.Either press 1, press 2, press 3, press 4, (press enter if used), or the method where you press all 4 buttons/keys at once and hold them for a short time.
The circuit you'll need depends on that.
The "press all at once" method takes very little circuitry and it doesn't even need logic chips - a few transistors and "glue" (R's and C's etc.) will do.
Each code key goes towards opening the lock after a delay and each non code key stops the delay from ever timing out, so just one wrong key keeps it from opening and if one of the code keys isn't pressed, the delay will never start.
The simplest "1 key at a time" can be made from eg. a 4017 and a 4093 (cheap and common) + glue.
Each output goes to a code key and if pressed a pulse is clocking the 4017 one step forward to the next code key. Any wrong or out of order key resets the circuit.
Decide which type you want to make and then see if you can figure out a way to do it.
If you get stuck, or if anything of the above is unclear, post what you have up to that point and we'll help you along.